Enhanced gas-phase oxidation of pollutants in exhaust plumes above oceans using chlorine radicals

Abstract

The invention provides a method for removing a pollutant (5) from a tropospheric space (500), wherein the method comprises: (A) injecting a chlorine-comprising compound (1) into a gaseous flow (50), wherein the gaseous flow (50) is provided in the tropospheric space (500) during daytime; wherein one or more of (a) the gaseous flow (50) and (b) the tropospheric space (500) comprise the pollutant (5); wherein the chlorine-comprising compound (1) comprises sodium hypochlorite; and (B) allowing the pollutant (5) to react with the chlorine radicals (2) produced from the chlorine-comprising compound (1).

Description

[0001] Enhanced gas-phase oxidation of pollutants in exhaust plumes above oceans using chlorine radicals

[0002] FIELD OF THE INVENTION

[0003] The invention relates to a method for removing a pollutant from a tropospheric space. The invention further relates to a pollution removal arrangement. Further, the invention relates to a target object comprising the pollution removal arrangement. The invention further relates to a computer program product comprising instructions to carry out the method of the invention. Further, the invention relates to a use of the pollution removal arrangement for removing methane slip of a target object.

[0004] BACKGROUND OF THE INVENTION

[0005] Methods for removing a pollutant from a tropospheric space are known in the art. For instance, W02010075856A2, describes a technical method for self-initiated cooling of the troposphere by enriching the same with at least one material from the group of inorganic chloride and bromide compounds. The materials used to this end are characterized by at least one of the properties: gaseous, vaporous below 500 °C, hygroscopic, and hydrolysable. The formation of the material used to this end is further characterized in the method procedure according to the invention by at least one of the steps: forming the material using saltwater electrolysis, forming the material without using combustion processes, and forming the material in the free troposphere.

[0006] US2024 / 091702 Al describes methods for the chemical sequestration of carbon dioxide (CO2), nitric oxide (NO), nitrogen dioxide (NO2) (collectively NOX, where x=l, 2) and sulfur dioxide (SO2) using closed loop technology. The methods recycle process reagents and mass balance consumable reagents that can be made using electrochemical separation of sodium chloride (NaCl) or potassium chloride (KC1). The technology applies to marine and terrestrial exhaust gas sources for CO2, NOx and SO2.

[0007] US2018 / 037308 Al describes a pollutant reduction device and method . The pollutant reduction device comprises: an exhaust gas pipe for discharging exhaust gas of a combustion engine; a cleaning water supply pipe for supplying cleaning water; a scrubber for spraying the cleaning water, which is supplied through the cleaning water supply pipe, at the exhaust gas flowing in through the exhaust gas pipe; and a cleaning water discharge pipe for discharging the cleaning water inside the scrubber and supplying the same to a ballast water tank.US2018 / 010500 Al describes a method for operating an internal combustion engine which has a gas combustion system and an exhaust gas post-treatment system. Exhaust gas that leaves the gas combustion system is directed to at least one CH4 oxidation catalytic converter of the exhaust gas post-treatment system. The CH4 / NO2 mole ratio in the exhaust gas is set in a defined fashion by at least one gas-combustion-system-side and / or exhaust-gas-post-treatment- system- side measure upstream of at least one CH4 oxidation catalytic converter.

[0008] SUMMARY OF THE INVENTION

[0009] Besides methane emissions reduction, atmospheric methane removal approaches are proposed to address increasing natural methane emissions, as well as anthropogenic methane emissions that cannot be mitigated with technology. If proven to be climate beneficial and cost-effective, open-system approaches likely have large potential scale and fast time to scale, with potential future temperature reduction of 0.5 °C.

[0010] Atmospheric methane oxidation (and therewith methane removal) enhancement may be achieved by lofting iron salt aerosols (ISA) into the atmosphere to catalytically generate chlorine radicals that oxidize methane. This approach may leverage the photocatalytic oxidation and reduction of Fe(II) and Fe(III) chlorides (mixed with NaCl salt) to produce Ch gas in the atmosphere. The iron-salt aerosols may for example be distributed through ship plumes, leveraging the updraft of warm air in the ship plume to carry the particles over large distances. However, the impact of such open-systems may be difficult to verify and there may be relatively large risks of unintended consequences compared to closed-systems.

[0011] Methane is naturally oxidized by hydroxyl (OH) radicals, resulting in an atmospheric lifetime of about 10 years for methane. The main source of OH may be ozone (O3), and the main source of the ozone may be NOx (defined as the sum of NO + NO2 + NO3), in the presence of sunlight and a fuel such as a hydrocarbon or CO (which may be consumed in the process of producing ozone). However, the amount of O3 and OH produced from NOXis selflimiting because (i) NOx may also react with O3 and (ii) NOx inhibits the efficiency of ozone production by removing OH to form HNO3. In other words the removal of NOx may reduce methane oxidation, except when NOXis removed from a high NOx background.

[0012] In marine areas, CI2 may be naturally formed through the reaction of chloride in particulate matter with one or more of HOC1, OH, CINO2 and CINO3. In addition chlorine atoms are may be produced through solar photolysis of one or more of CI2, CINO3, BrCl, IC1, CINO2 and HOC1, and through the bimolecular reaction of HC1 and CIO with OH. When CI2 is artificially added to the atmosphere (for the intention of removing pollutants such as methane),it may absorb sunlight and dissociate to form two Cl radicals (also known as Cl atoms) that can oxidize methane, and thus help to remove it. However, the added Cl or Ch will also cause a reduction in O3 and especially in NOx. In many cases, this may lead to less OH production, which may cancel or exceed the direct effect of Cl removing methane, except when the Cl emission is high enough to overcome this effect. In other words, the loss of OH from Cl emissions may decrease with increasing Cl concentration. However, if Cl is added to an air mass with high NOXlevels (such as a ship plume), then it may work in the opposite way and may help to increase methane oxidation. Unfortunately, for ships emitting iron-salt aerosol to produce chlorine, most of the ocean regions have unfavorable NOx conditions, leading to methane increase instead of removal.

[0013] The direct release of Ch gas into the atmosphere for the purpose of oxidizing atmospheric methane may be considered. However, it appears that the direct release of Ch gas may not always lead to a net methane removal because the chlorine addition can lead to ozone loss, which may reduce the main sink of methane (OH radicals). In contrast to this, high intensity CI2 emissions efficiently removed methane. Further, the direct release of iron chloride species into the atmosphere, to produce Ch indirectly via iron-salt aerosol formation, may be considered. However, it seems that high iron emissions would be needed to efficiently remove methane with shipping iron emissions, therewith increasing cost and risk.

[0014] There may thus be a need for methods to remove pollutants (such as methane, volatile organic compounds, ozone and NOx) from an exhaust located in a maritime region (having proximity to ocean), especially methods to remove methane slip from the exhaust of ships comprising methane in their fuel. The use of methane as fuel on ships was introduced as it would potentially reduce emissions of pollutants and CO2, but it seems that a significant amount of methane passes through the engine unbumed. This so-called ‘methane slip’, which may vary depending on engine type and operation, may undo the environmental benefits of liquefied natural gas as a fuel.

[0015] Solutions to improve engine performance may help reduce emissions somewhat, but would only provide a partial solution. One of the fundamental difficulties may be that methane is unusually inert and resists chemical reaction; the CH bonds in methane may be the least reactive of any hydrocarbon C«Hm. This chemical resistance to reaction results in ~10 years atmospheric lifetime of methane.

[0016] Solutions such as the use of catalyst surfaces to reduce (atmospheric) methane (slip) may not address the problem sufficiently, because the concentration of the pollutants may be too low to be captured or destroyed efficiently by surface-based solutions.Gas-phase advanced oxidation, using reactors with hydroxyl radicals or chlorine radicals, on the other hand may not be suited for application in ship plumes above the ocean. Disadvantages of hydroxyl-based reactor solutions may further be that these methods may not be selective enough for methane removal, and concentrations of hydroxyl cannot be increased to high enough level to remove enough methane. As the concentration of OH is increased the chemical mechanism becomes self-limiting because OH may react with itself and with its precursor, therewith limiting the concentration that can be achieved in an efficient manner. The concentration that can be achieved may not be high enough to yield a device with a reasonable throughput.

[0017] A chlorine-based gas-phase advanced oxidation approach may be based on the use of a reactor in which Ch gas (i) is photolyzed with a UV light source, and then (ii) chemically interacts with the pollutants in the exhaust gas. A disadvantage thereof may be that the UV light source negatively affects the energy efficiency, because for such systems the energy of the UV light source may be the main input energy. In addition, the problem with such systems may be that it may not be suited for exhaust plumes that contain a high concentration of particulate mass (smoke), because the smoke may block the UV light and foul the surfaces of the lights. Moreover, a reactor based solution may not be efficient enough for low concentrations of methane below about 20 ppm. Furthermore, Ch is a hazardous substance that may be too risky to carry on board of a ship.

[0018] Another chlorine-based gas-phase advanced oxidation approach may be based on the use of iron-salt aerosols to produce Ch gas in the open air within the exhaust plume. A disadvantage thereof may be that the efficiency of methane removal depends on NOXconditions, and over most of the ocean surface the conditions are such that the Ch produced by the iron-salt aerosols will reduce ozone levels and will increase methane levels (the opposite of the aim of the invention). Only in the vicinity of the ship may the NOx conditions be favorable to methane removal (due to the NOx emission of the ship itself), but because the plume disperses rapidly and iron-salt aerosols have several days of atmospheric lifetime, the iron-salt aerosol approach does not benefit from the favorable conditions close to the ship. An additional problem with the iron-salt aerosol approach may be related to the long atmospheric lifetime of the particles, which may lead to concerns on global environmental implications, and on global governance. In addition, the iron particles also can cause some wanning themselves, partially cancelling benefits from methane removal.

[0019] A particular problem may thus be that possible methane removal approaches may not be suitable, due to (expected) low efficiency, high capital and / or running cost or dueto unwanted environmental impact. Hence, it is an aspect of the invention to provide an alternative method for reducing and / or removing a pollutant, especially methane, from a tropospheric space , which preferably further at least partly obviates one or more of abovedescribed drawbacks. The present invention may have as object to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

[0020] According to a first aspect, the invention provides a method for removing a pollutant from a tropospheric space. The method (in a first stage) may especially comprise injecting a chlorine-comprising compound into a gaseous flow. In embodiments, the gaseous flow (comprising the chlorine-comprising compound) may be provided in (such as released or emitted into) the tropospheric space during daytime. In further embodiments, one or more of (a) the gaseous flow and (b) the tropospheric space may comprise the pollutant. In embodiments, the chlorine-comprising compound may comprise sodium hypochlorite (NaOCl). Furthermore, in embodiments, the method (in a second stage) may comprise allowing the pollutant to react (in the tropospheric space) with the chlorine radicals produced from the chlorine-comprising compound. Especially, in embodiments, the method (in the second stage) may comprise allowing the pollutant to be oxidized (in the tropospheric space) by the chlorine radicals produced from the chlorine-comprising compound. Hence, in specific embodiments, the invention may provide a method for removing a pollutant from a tropospheric space, wherein the method may comprise: (A) injecting a chlorine-comprising compound into a gaseous flow, wherein the gaseous flow (comprising the chlorine-comprising compound) may be provided in (such as released or emitted into) the tropospheric space during daytime; wherein one or more of (a) the gaseous flow and (b) the tropospheric space may comprise the pollutant; wherein the chlorine-comprising compound may comprise sodium hypochlorite (NaOCl); and (B) allowing the pollutant to react (in the tropospheric space) with (especially be oxidized by) the chlorine radicals produced from the chlorine-comprising compound. Hence, in specific embodiments, the invention provides a method for removing a pollutant from a tropospheric space as further defined in claim 1.

[0021] In another aspect, the invention provides an alternative method for removing a pollutant from a tropospheric space. In embodiments, the method may comprise providing a chlorine-comprising compound in the tropospheric space. The chlorine-comprising compound may especially be provided in the tropospheric space during daytime. Further, in embodiments, the pollutant may also be provided to the tropospheric space. Additionally or alternatively, in embodiments, the tropospheric space may (already) comprise the pollutant. The method may further, in embodiments, comprise allowing the chlorine-comprising compound to producechlorine radicals in the tropospheric space. Yet further, in embodiments, the method may comprise allowing the pollutant to react with the chlorine radicals produced by the chlorinecomprising compound. Hence, in specific embodiments, the invention may provide a method for removing a pollutant from a tropospheric space, wherein the method comprises:

[0022] providing a chlorine-comprising compound in the tropospheric space during daytime; wherein one or more of the following applies (a) the pollutant is also provided to the tropospheric space , and (b) the tropospheric space comprises the pollutant; and

[0023] allowing the pollutant to react, in the tropospheric space, with chlorine radicals produced from the chlorine-comprising compound.

[0024] Further, in specific embodiments, when a wind flows, the method may comprise releasing the chlorine-comprising compound in the wind. As such, the wind may be used to provide the chlorine-comprising compound into the tropospheric space. Hence, in embodiments, when a wind flows, the chlorine-comprising compound is released in the wind.

[0025] This invention thus may provide a method for removing a pollutant from a tropospheric space. Especially, the method of the invention may comprise injecting a Cl-comprising compound, such as Ch or especially NaOCl, into an exhaust of a ship during daylight conditions so that the pollutant may be removed in the open air and close to the ship. The use of NaOCl may especially be preferred, because it may have lower environmental impact (for example low impact on atmospheric and ocean acidity) and may be relatively safer (for human health) compared to Ch. Moreover, the method may provide a relatively cheap way to remove even low concentrations of pollutants from a maritime region making use of already existing infrastructures.

[0026] The invention may thus provide a method removing a pollutant from a tropospheric space. Herein, the term “pollutant” may especially refer to a substance (such as a gaseous compound) that pollutes the atmosphere. In embodiments, the pollutant may especially comprise one or more of the group comprising: methane, a volatile organic compound (VOC), ozone, and nitrogen oxides (NOx). Additionally, in embodiments, the pollutant may comprise reduced sulfur gasses, such as e.g. H2S. Herein, NOx may be defined as the sum of NO + NO2 + NO3. For example, in embodiments, the pollutant may comprise an exhaust gas constituent, such as one generated through the operation of a combustion engine. In embodiments, the pollutant may comprise ozone. The ozone concentration in ship plumes may often be depleted close to the ship (due to relatively high NOx concentrations close to the ship, that temporarily store ozone pollution), followed by an increase in ozone pollution further away (when NOx concentrations go down). In embodiments, the emission of the chlorine-comprisingcompounds, through the reduction in NOx, and the reduction of methane (as being one of the most important precursors for tropospheric ozone formation globally), may also reduce ozone levels in the tropospheric space.

[0027] In specific embodiments, the pollutant may comprise methane. Methane may be naturally oxidized by a radical called hydroxyl (OH), resulting in an atmospheric lifetime of about 10 years for methane. The term “atmospheric methane oxidation” may herein thus refer to the breakdown of methane present in the atmosphere, even though oxidation may not be the only method for breaking down methane. The limited atmospheric lifetime, about 10 years, of methane may be due to substantial methane sinks. The primary methane sink may be atmospheric oxidation, from hydroxyl radicals (as described above) and chlorine radicals. The rest of the atmospheric methane may be primarily consumed by methanotrophs and other methane-oxidizing bacteria and archaea in soils. Herein, enhanced atmospheric methane oxidation may especially refer to a category of approaches to accelerate such breakdown of methane present in the atmosphere, for the purpose of further mitigating some of the impacts of climate change.

[0028] In embodiments, the enhanced atmospheric methane oxidation may be due to a local emission of an enhancing compound, such as a chlorine-comprising compound. Herein, the term “chlorine-comprising compound” may especially refer to a compound comprising the chemical element chlorine (i.e. the chemical element of atomic number 17), i.e., comprising a chlorine atom. Moreover, the term “chlorine-comprising compound” may herein refer to a compound comprising the chemical element chlorine, wherein the elemental chlorine may have an oxidation state (i.e. a hypothetical charge if all of its bonds to other atoms are ionic) of 0 or +1. For example, in embodiments, the chlorine-comprising compound may comprise Cb, which has an oxidation state of 0. Alternatively, in embodiments, the chlorine-comprising compound may comprise sodium hypochlorite, which has an oxidation state of +1. Such chlorine atoms as comprised by the chlorine-comprising compound may, in embodiments, function as precursors for chlorine atoms (or chlorine radicals) in the atmosphere (upon execution of the method).

[0029] In embodiments, when chlorine (Cb) gas is (directly) added to the atmosphere, it may generate chlorine radicals that can oxidize methane, and therewith may enhance the natural methane oxidation. Hence, in some embodiments, the method of the invention (in a stage (i)) may comprise injecting Cb (gas) into the tropospheric space. In embodiments where the chlorine-comprising compound may be chlorine (Cb) gas, preferably the gaseous flow may include high concentrations of NOx (see also further below).Alternatively, in embodiments, the method of the invention (in a stage (i)) may comprise injecting a chlorine-comprising compound (configured to (indirectly) release Cb into the air) into the tropospheric space. Especially, in embodiments, by lofting a chlorinecomprising compound, such as NaOCl, into the atmosphere, chlorine gas (Ch) may be generated (e.g. through reactions with acids) to produce CI2 gas in the atmosphere, which may be photolyzed (by absorbing sunlight) to produce Cl radicals, which may oxidize methane. Hence, in embodiments, the chlorine-comprising compound may comprise sodium hypochlorite (NaOCl). Sodium hypochlorite may, in embodiments, be aerosolized. Especially, in such embodiments, the aerosolized sodium hypochlorite may be converted to Ch when it is mixed with acids (such as HC1, see also further below) in the atmosphere. An advantage of such embodiments may be that NaOCl emissions generally may not increase the acidity of the atmosphere and the ocean (instead it may have a slight alkaline effect). For CI2 emissions, a problem may be that the end result of the reaction chain may typically be two HC1 molecules, which may increase the acidity of the atmosphere or the ocean (where the HC1 will deposit). The use of NaOCl as the chlorine-comprising compound may overcome this problem. NaOCl itself may be slightly alkaline (in water it forms NaOH - a strong base, and HOC1 - a weak acid), and the reaction chain starting with a reaction of NaOCl+2HCl— >C12+NaCl+H2O may consume two HC1 molecules (a strong acid), and then produce two new HC1 molecules (CI2 eventually leading to two HC1 molecules). Thus, following the reaction chain (or mechanism) the number of acid molecules in the atmosphere and ocean may not change with the emission of NaOCl, which may be a great advantage in view of environmental impact. For HOC1 emissions (instead of Cb), the end result of the reaction chain may typically be one HC1 molecule (instead of two for CI2), which may result a slightly lower increase in acidity of the atmosphere or the ocean (where the HC1 will deposit) compared to Ch, though still higher than compared to the use of NaOCl emissions. Thus, the use of NaOCl may also be advantageous over the use of HOC1. In addition, HOC1 may escape from aerosols to the gas-phase, resulting in a change, such as a loss, in atmospheric lifetime, while such loss occurs less to not at all for NaOCl.

[0030] Note, however, that in the atmosphere NaOCl may be converted into HOC1. In principle, through uptake (capturing) of CO2, the NaOCl in the atmosphere may be converted into HOC1, which may lead to a (temporary) increase in HC1 concentrations in the atmosphere. In other words, in the atmosphere, essentially some CO2 may be converted into HC1 via HOC1 using the NaOCl provided into the atmosphere, therewith (temporarily) acidifying the atmosphere. This may have the advantage of accelerating the conversion of NaOCl to Cb.However, the aforementioned increase in acidity may be temporary, because the additional HC1 may be consumed in a reaction with the captured CO2 to release the CO2 again. Nonetheless, the use of NaOCl and / or Cb as chlorine-comprising compounds may provide beneficial effects to CO2 reduction in cases where the produced HC1 is neutralized (for example by reaction with silicate minerals in rocks or dust). Hence, in embodiments, the NaOCl may be released in a tropospheric space that is affected by silicate mineral dust (such as the ocean region affected by Patagonia dust), or released downstream from a rocky area with silicate rocks, such as for example olivine. Another advantage of embodiments where the chlorine-comprising compound comprises NaOCl may be that such a method may be relatively safe for human health compared to direct emission of CI2 gas. Through the use of NaOCl, chlorine gas concentrations close to the target object may be at least lOx lower, therewith protecting the crew and the environment around the ship against exposure to high Ch concentrations. Furthermore, the use of NaOCl as the chlorine-comprising compound may provide the benefit of adjustability of the lifetime of the compound through its particle size and composition, which may be changed by changing the dilution of the compound. Smaller NaOCl aerosols may have a relatively higher surface area, due to which they can take up relatively more HC1 for the same HC1 background concentration. For a given particle size, if the dilution is higher (less NaOCl per volume), then the total number of aerosols may be increased for the same amount of NaOCl, again resulting in a higher surface area density and therefore a higher uptake of HC1.

[0031] Additionally or alternatively, in embodiments, the chlorine-comprising compound may comprise another compound configured to (indirectly) release Ch into the air, such as an inorganic chloride selected from the group comprising: a hypochlorite other than sodium hypochlorite (such as Ca(OCl)2, LiOCl, and KOC1), chlorites (such as NaCICh, Mg(C102)2, and KCIO2), chlorates (such as NaCICL, and KCIO3), and hypochlorous acid (HC1O). Especially, in embodiments, the chlorine-comprising compound may comprise another compound configured to (indirectly) release CI2 into the air, such as an inorganic chloride selected from the group comprising: a hypochlorite other than sodium hypochlorite (such as Ca(OCl)2, LiOCl, and KOC1), chlorates (such as NaCIO?,. and KCIO3), and hypochlorous acid (HC1O). The hypochlorites may especially be converted to Ch when it is mixed with acids (such as HC1, see also further below) in the atmosphere. Conversely, the chlorates may be converted to CI2 (i) under heating and / or (ii) under exposure to strong acids such as HC1. Additionally or alternatively, the chlorates may be converted to CI2 under exposure to UV light, such as sunlight. Furthermore, hypochlorous acid (which may be naturally formed in bleach solutions) may readily release chlorine gas after uptake by acidicaerosols in the atmosphere. Furthermore, chlorites may be oxidized to hypochlorite by reaction with e.g. O3, OH or H2O2.

[0032] In embodiments, the chlorine-comprising compound may especially be injected into the gaseous flow. The gaseous flow may, in some embodiments, comprise an exhaust stream (or plume) of a target object, such as from operation of a combustion engine of the target object (e.g. from a ship, see also further below). Additionally or alternatively, the gaseous flow may be provided by a flow generating device, such as e.g. a chimney or flare stack. Furthermore, in embodiments, the step of injecting the chlorine-comprising compound into the gaseous flow may be performed during daytime. An advantage of such embodiments may be that photolysis may occur under the influence of sunlight, therewith allowing the chlorinecomprising compound to be converted into chlorine radicals, see also further below. The term “daytime” may refer to the period between dawn (sunrise) and dusk (sunset). For instance, in embodiments in the method of the invention, a concentration of the chlorine-comprising compound may increase from sunrise to about noon, and then decrease again until sunset. In embodiments, the timing of when the chlorine-comprising compound may be injected into the gaseous flow may be dependent on the (expected) atmospheric lifetime of the chlorinecomprising compound. The injection of the chlorine-comprising compound into the gaseous flow may, in embodiments, be initiated and terminated depending on the (expected) atmospheric lifetime of the chlorine-comprising compound and the expected sunrise and sunset times of each respective day, such that the daytime may be optimally exploited. For example, in embodiments, if the lifetime of the chlorine-comprising compound may be 3 hours, then the injection of the chlorine-comprising compound into the gaseous flow may be terminated around about 3 hours prior to sunset. In embodiments, the method may comprise injecting the chlorine comprising compound into the gaseous flow during an injection timeframe. The injection timeframe may, in embodiments, be defined from sunrise up to sunset, especially from sunrise up to a moment during the day approximately the length of the atmospheric lifetime of the chlorine-comprising compound prior to sunset. For example, in embodiments, the injection timeframe may be from about 1 hour prior to sunrise to about 1 hour before sunset. Such an example may be beneficial as the emission may be initiated at a timepoint where the chlorinecomprising compound may be activated to produce chlorine radicals while the gaseous flow (e.g. ship plume) may not yet be (too much) dispersed. Moreover, such an example may be beneficial as the emission may be terminated at a timepoint where the chlorine-comprising compound may be substantially fully activated to produce chlorine radicals before the sun has fully set. Hence, herein, for example chlorine-comprising compounds may not be emitted atessentially any time as may be the case as a result of chemical processes that leak chlorinecomprising compound, such as performed in reactor-based exhaust-gas treatment systems. Especially, in embodiments, the step of injecting the chlorine-comprising compound into the gaseous flow may not be performed during nighttime, i.e., emission of the chlorine-comprising compound into the gaseous flow may be substantially turned off during nighttime. Herein, the phrase “the step of injecting the chlorine-comprising compound into the gaseous flow may not be performed during nighttime” may especially indicate that emission of the chlorinecomprising compound into the tropospheric space during nighttime may be at least 100 times less than, such as 50 times less than, such as even essentially zero times, the amount of chlorinecomprising compound being emitted during the daytime. Herein, the emissions during nighttime and during daytime may especially be averaged over the day and averaged over the night, respectively. Hence, in embodiments, average nighttime emissions of the chlorinecomprising compound into the gaseous flow may be 25 times less than, such as 10 times less than, like 5 times less than the average day-time emissions of the chlorine-comprising compound into the gaseous flow. Such embodiments may provide the advantage that wasted emission of the chlorine-comprising compound may be avoided, as emission of chlorinecomprising compound during nighttime may not lead to reduction of the pollutant due to the lack of photochemical activation (that would be provided by the sun during daytime conditions). Yet, the injection timeframe may be within a time period selected from about 1 hour prior to sunrise to about 1 hour before sunset, or in specific embodiments be within a time period selected from about sunrise to about sunset. The injection timeframe my be during the whole time period, or during part of it, and may also be intermittently within this time period.

[0033] In embodiments, (the injection rate of) injection of the chlorine-comprising compound may be reduced (and terminated) gradually or all at once. Hence, in embodiments, the method may comprise (i) injecting the chlorine-comprising compound in a(n active) concentration X into the gaseous flow during the injection timeframe (i.e. from sunset to approximately the atmospheric lifetime of the chlorine-comprising compound prior to sunset), and (ii) reducing and terminating injection of the chlorine-comprising compound during a timeframe from approximately the atmospheric lifetime of the chlorine-comprising compound prior to sunset up to sunset, such that an inactive concentration Y is achieved, wherein Y<0.05*X, such as Y<0.01*X.

[0034] Further, in embodiments, one or more of the gaseous flow and the tropospheric space may comprise the pollutant.In embodiments, the gaseous flow may comprise the pollutant. The gaseous flow may, in some embodiments, comprise an exhaust stream (or plume) of a target object, such as from operation of a combustion engine of the target object (e.g. from a ship, see also further below). An advantage of such embodiments may be that the chlorine-comprising compound may be provided into a polluting stream directly, therewith enabling its reacting with pollutants present in the gaseous flow (i.e., in the exhaust stream). In specific embodiments, the (gaseous flow, especially the) exhaust stream may thus comprise the pollutant. Further, in embodiments, the gaseous flow may be provided in (such as released or emitted into) the tropospheric space. Such embodiments may be beneficial as the gaseous flow may disperse the chlorine-comprising compound, therewith enabling its reacting with the pollutant. In some embodiments, the pollutant may thus be present in the (gaseous flow especially the) exhaust stream itself. Alternatively, in embodiments, the exhaust stream may not comprise the pollutant. Especially, in such embodiments, the pollutant may be atmospherically present in the tropospheric space. In other words, in such embodiments, the method may be used for removing general pollution from the atmosphere. Hence, in embodiments, the gaseous flow may disperse the chlorinecomprising compound into the tropospheric space, therewith enabling its reacting with the pollutant present in the atmosphere, regardless of whether the gaseous flow itself comprises the pollutant.

[0035] In yet other embodiments, the pollutant may be comprised in the gaseous flow but may also be present in the tropospheric space.

[0036] In embodiments, the chlorine-comprising compound may especially be emitted (i.e., injected) in the tropospheric space.

[0037] Herein the term “tropospheric space” may especially refer to a volume or area defined in the troposphere, i.e., in the lowest layer of the atmosphere of earth (extending up to about 20 kilometers above the earth’s surface). In embodiments, the tropospheric space may especially be defined above an ocean or a sea. Herein, the terms “ocean” and “sea” may be defined as (relatively large) bodies of salt water, especially bodies of water as distinguished from the land and the air. Moreover, in embodiments, the tropospheric space may herein be defined as a space (or volume) directly over the sea surface and (the space) having a height (hi) (relative to the sea surface) selected from the range of 0.5-4 km, such as from the range of 1 -3 km, such as about 2 km. Therewith, in embodiments, the tropospheric space may especially be defined within a marine boundary layer, i.e., within a part of the atmosphere that has direct contact with (and hence may be directly influenced by) the ocean (or sea).. In embodiments, the surface may comprise one of a sea surface, an ocean surface, but in embodiments also asurface above a virtual plane Vp at land at sea-level. Herein, the term “sea-level” may especially be defined as the altitude level of the sea surface, which may be denoted as 0 m. The height (hi) at which the tropospheric space is located may be selected from the range of 0.5-4 km, such as from the range of 1-3 km, such as about 2 km above the surface. Hence, in embodiments, the tropospheric space may be defined as a space (or volume) defined at a height (hi) above a sea surface, an ocean surface, or above a virtual plane Vp at land at sea-level, wherein the height (hi) may be selected from the range of 1-4 km.

[0038] Especially, in embodiments, the method may be executed preferably in the vicinity of a sea or ocean. Hence, in embodiments, tropospheric space may be in a maritime region. In such embodiments, the maritime region may be defined as either above the sea surface or having a maximum distance from the closest coastline. Additionally or alternatively, the maritime region may be defined as above the ocean surface. Additionally or alternatively, the maritime region may be defined as a region that is impacted by sea spray aerosols, such as e.g. a region above the sea, or a region above the land where air (comprising sea spray aerosols) is blown over from the sea. Thus, in embodiments, the tropospheric space may be in a region close to or impacted by the sea. Yet additionally or alternatively, the maritime region may be defined as above the virtual plane Vp at land at 0 m (i.e., at sea-level) height but within a shortest distance di of 3 km from an ocean or a sea, such as within a shortest distance di of 2 km, like within a shortest distance di of 1.5 km. In embodiments, the shortest distance di (between the virtual plane Vp at land and a sea or ocean) may be selected from the range of 0-8 km, such as from the range of 0.5-6 km, like from the range of 1 -5 km, especially from the range of 1 -4 km. Hence, the term “maritime region” may refer to sea or ocean, and also to land within 3 km from an ocean or sea. Especially, the term “maritime region” may be defined as a space or volume defined at a height (hi) as measured from sea-level (a) above the sea surface, (b) above the ocean surface, or (c) above an area of land within a shortest distance (di) of 3 km from an ocean or a sea. The height of the tropospheric space over land (in a maritime region) is especially defined as an average height relative to sea level.

[0039] Herein, the terms “ocean” and “sea” may be defined as (relatively large) bodies of salt water, especially bodies of water as distinguished from the land and the air. Hence, in embodiments the chlorine-comprising compound may especially be emitted in a space 20 kilometers above the sea surface and (the space) having a height of about 2 km. Note that the term “sea surface” may also refer to the surface of an ocean.

[0040] In embodiments, the chlorine-comprising compound may be a precursor for chlorine radicals. Especially, in embodiments, under atmospheric conditions (in thetropospheric space) the chlorine-comprising compound may be converted into chlorine gas (,the chlorine-comprising compound may thus be a precursor for chlorine gas, and the resulting chlorine gas may be a precursor of chlorine atoms, i.e., the chlorine-comprising compound may be an (indirect) precursor for chlorine atoms). More especially, in embodiments, the chlorinecomprising compound may react with an acid (or an acid precursor) such that the chlorinecomprising compound may be oxidized into chlorine gas.

[0041] In embodiments where the tropospheric space is especially defined above a maritime region, the maritime region may provide a sufficient concentration of acid, such as hydrochloric acid (HC1), in the tropospheric space. Especially, in embodiments, the tropospheric space may comprise an acid. Additionally or alternatively, in embodiments, the tropospheric space may comprise an acid precursor. In embodiments, the tropospheric space may comprise the acid (precursor)in a concentration of at least 50 ppt, such as at least 100 ppt, like at least 200 ppt. In embodiments, the concentration of the acid (precursor) may especially be chosen (e.g. through the local addition of acid via the gaseous flow, see also below), such as to ensure a relatively short atmospheric lifetime of the chlorine-containing compound. Moreover, in embodiments, the tropospheric space may comprise the acid (precursor) in a concentration of at most 400 ppt, such as at most 200 ppt, like at most 100 ppt. Alternatively, in embodiments, the tropospheric space may comprise the acid (precursor) in a concentration of at most 3 ppb, such as at most 2 ppb, like at most 1 ppb. For example, the tropospheric space may comprise the acid (precursor) in a concentration selected from the range of 1-3 ppb.

[0042] In embodiments, the concentration of the acid (precursor) may especially be chosen, such as to ensure a relatively long atmospheric lifetime of the chlorine-containing compound. Whether the atmospheric lifetime is preferred to be longer or shorter may depend on the specific application, as explained in other embodiments. Furthermore, in embodiments, the acid ( precursor) may be selected from the group comprising: HC1, HNO3, H2SO4, SO2, NO2, and HCOOH. Such embodiments may be beneficial as the acid (precursor) may aid in converting the chlorine-comprising compound into chlorine gas in a relatively short space of time.

[0043] As described above, it may be desirable to choose (or influence) the acid (precursor) concentration in the tropospheric space to therewith influence the atmospheric lifetime of the chlorine-comprising compound. Therefore, additionally or alternatively, in embodiments, the method may comprise providing an acid or an acid precursor in the gaseous flow. By providing the acid (precursor) in the gaseous flow, the acid (precursor) concentration may locally be increased within the atmospheric space. Hence, in embodiments, the gaseousflow may comprise an acid. Additionally or alternatively, in embodiments, the gaseous flow may comprise an acid precursor. In embodiments, the gaseous flow may comprise the acid (precursor) in a concentration of at least 50 ppt, such as at least 750 ppt, like at least 100 ppt. Moreover, in embodiments, the gaseous flow may comprise the acid (precursor) in a concentration of at most 1000 ppt, such as at most 500 ppt, like at most 250 ppt. Yet alternatively, in embodiments, the gaseous flow may comprise the acid (precursor) in a concentration of at most 100 ppm, such as at most 1 ppm, like at most 100 ppb, especially at most 50 ppb. In particular, in embodiments, the gaseous flow may comprise the acid (precursor) in an amount selected from the range of 0.1-100%, such as 0.1-25% of the amount of chlorinecomprising compound (in mol) injected into the gaseous flow. For example, in embodiments where NaOCl (as the chlorine-comprising compound) is injected into the plume of a ship, if 20 g (in case of NaOCl this may be about 0.27 mol) chlorine-comprising compound per kg of fuel consumed is injected, then the acid (precursor) may be added in an amount selected from the range of 1-100% of 0.27 mol. In other words, in this example, if 0.27 mol NaOCl (as the chlorine-comprising compound) per kg of fuel consumed is injected, then the acid (precursor) may be added in an amount selected from the range of 0.27-27 mol. Especially, in embodiments, the gaseous flow may comprise the acid (precursor) in an amount selected from the range of 1-100%, such as selected from the range of 1-25%, especially from the range of 5-20%, like from the range of 10-15% of the amount of chlorine-comprising compound injected into the gaseous flow.

[0044] In embodiments, the acid (precursor) may be selected from the group comprising: HC1, HNO3, H2SO4, SO2, NO2, and HCOOH. Moreover, in embodiments, the acid (precursor) may comprise one of CI2 or HOC1. Such embodiments may be beneficial as the acid (precursor) may be provided in the tropospheric space no matter where said space may be defined (e.g. above land rather than sea), therewith aiding in converting the chlorinecomprising compound into chlorine gas in a relatively short space of time without being dependent on a maritime region. The use of CI2 or HOC1 as acid precursor may be beneficial, because the HOC1 or CI2 may both remove some methane and produce HC1 acids, therewith providing synergy between methane removal and providing acidity to convert for example NaOCl into Ch further downstream. Thus, in a specific embodiment, the chlorine comprising compound may be NaOCl and in addition CI2 or HOC1 may be added to the gaseous flow (as an acid (precursor)). Moreover, in embodiments, the chlorine comprising compound may also comprise a mixture of NaOCl and CI2 or HOC1.In embodiments, the chlorine-comprising compound may have an atmospheric lifetime (in the tropospheric space) of less than 8 hours (during daytime). Herein, the term “atmospheric lifetime (in the tropospheric space)” may be defined as the inverse of a loss-rate (or rate of decay) of the respective compound. For a first-order reaction, the rate of decay (or removal) of a compound may be proportional to its concentration. The mathematical expression for a first-order reaction's rate constant (k) may be given by: d[A] / dt = -k [A], where [A] may be the concentration of the compound. The atmospheric lifetime (r) of a compound in the atmosphere may be related to the rate constant (k) of its removal processes (such as e.g. chemical reaction, like oxidation, or deposition). The atmospheric lifetime may, in embodiments, be calculated as: r=l / k. For example, if the first order reaction rate is 0.00028 per second, then the atmospheric lifetime (according to this definition) may be 3600 seconds (i.e., 1 hour). The atmospheric lifetime may thus refer to the (average) time between entrance of the respective compound into the tropospheric space and the compound being (i) dispersed outside the tropospheric space and / or (ii) oxidized away. The lifetime of the chlorinecomprising compound may thus determine how fast it may be converted into Cl atoms, which may be used to remove pollution (including methane). For example, if the chlorine-comprising compound comprises Ch, the lifetime may usually be less than 1 hour, typically in the order of tens of minutes (due to rapid photolysis by sunlight, which produces two Cl atoms from one Ch molecule). This means that most of the Ch may be converted into Cl atoms within 1 hour, within whatever distance air is transported during that time (for example 5 km if the relative wind speed compared to the source (e.g. ship) is 5 km / h). The short lifetime may provide the advantage of insurance that the Cl atoms may remove pollution in the vicinity of the source (e.g. ship) before being dispersed too far and that the environmental impact may be local.

[0045] According to the invention, in embodiments, the chlorine-comprising compound may have an atmospheric lifetime of less than 8 hours, preferably less than 3 hours, and more preferably less than 1 hour. As such efficient methane removal may be achieved due to relatively high local Cl concentrations. Moreover, if the atmospheric lifetime of the chlorinecomprising compound is longer than one minute, an additional benefit may be that the chlorinecomprising compound may be mixed with the gasses in the (gaseous flow and especially in the) atmosphere due to turbulent diffusion. The efficiency of methane removal may further be improved by high NOXconcentrations, which may e.g. be present in the case where the gaseous flow comprises an exhaust stream (e.g. of a ship).

[0046] Especially, in embodiments, the chlorine-comprising compound may have an atmospheric lifetime (in the tropospheric space) of at least 15 minutes (during daytime), suchas at least 30 minutes, especially at least 60 minutes, like at least 120 minutes. Further, in embodiments, the chlorine-comprising compound may have an atmospheric lifetime (in the tropospheric space) of less than 8 hours (during daytime), such as less than 6 hours, like less than 4 hours, especially less than 3 hours. In specific embodiments, the chlorine-comprising compound may have an atmospheric lifetime (in the tropospheric space) of at least 30 minutes and less than 8 hours, especially at least 1 hour and less than 3 hours.

[0047] Longer lifetime of the chlorine-comprising compound may be undesirable because with longer lifetime deposition of the compound to the ocean surface becomes increasingly important, leading to loss of chlorine-comprising compound without removing pollutant. A situation when a 8 hour lifetime may be preferred, may, in embodiments, be when it is required to increase the total emission of the chlorine-comprising compound, and safety limits cannot achieve this with shorter lifetimes. An advantage of a relatively long lifetime (up to 8 hours) may be that a higher methane removal capacity can be achieved with one emission source.

[0048] On the other hand, a short lifetime of the chlorine-comprising may provide more control over the environmental impact of the chlorine-comprising compound emissions, because effects occur within the proximity of the source (e.g. ship), and can therefore be better checked and controlled. Moreover, a short lifetime of the chlorine-comprising may result in lower loss due to deposition, or due to night-time dynamics.

[0049] As described above, in embodiments, the chlorine-comprising compound may be converted (such as oxidized) into chlorine gas. The chlorine gas may, in embodiments, be converted (such as photolyzed) into chlorine radicals. Hence, in embodiments, the chlorinecomprising compound may be a precursor for chlorine radicals, (optionally via chlorine gas,) under atmospheric conditions (in the tropospheric space).

[0050] In embodiments, the method of the invention (in a stage (ii)) may further comprise allowing the pollutant to react with the chlorine radicals. Especially, in embodiments, the method may comprise enabling the pollutant to be oxidized (in the tropospheric space) by the chlorine radicals (produced from the chlorine-comprising compound). Hence, in embodiments of the method, in the tropospheric space, the chlorine-comprising compound may be converted into chlorine radicals (optionally via chlorine gas) which may react with (such as oxidize) the pollutant.

[0051] The method may further (in the stage (i)) comprise injecting the chlorinecomprising compound into the gaseous flow, such as into a gaseous flow as provided by a target object. For example, in embodiments, the target object may comprise a vessel. In embodiments,the vessel may be selected from the group comprising: a ship, a barge, a yacht, an oiler, a buoy, and a tanker. The vessel may especially comprise an exhaust device (such as a chimney) configured to provide an exhaust stream. For example, in embodiments, the target object may comprise a vessel such as a ship. The ship may especially be configured to produce a ship plume, i.e., an exhaust stream. In such embodiments, the gaseous flow may thus comprise the exhaust stream of the vessel. The advantage of applying the method on a vessel with an exhaust stream may be that the exhaust may already include pollutants to be removed, such as methane pollution from methane slip. Further, the exhaust device on the vessel may be designed in such a way that crew may remain at safe distance from the exhaust stream, which then also applies to emissions of the chlorine-comprising compound. Moreover, vessel may be operated at sea, wherewith providing easy and cheap access to sea water for producing the chlorine-comprising compound. Additionally, due the maritime region in which vessel may be operated, (i) acid species such as HC1 resulting from pollutant removal may deposit in the ocean, and (ii) above the oceans HC1 concentrations may be relatively high, which may be beneficial for the conversion of the chlorine-comprising compound (especially NaOCl) into the chlorine radicals. Furthermore, the method of the invention may be used for the removal of a plurality of pollutants such as: (i) soot deposition closer to vessel (by converting hydrophobic soot to hydrophilic soot), reducing climate impact, (ii) SO2, therewith reducing acid rain issues, (iii) volatile organic compounds, (iv) NOx, and (v) ozone.

[0052] As described above, high NOx concentrations may be favorable for methane removal. Thus, there may be a synergy between NOx emissions by the exhaust stream and removal of methane with emissions of chlorine-comprising compounds in the exhaust stream. Therefore, in a preferred embodiment, the exhaust stream may comprise NOx pollution. NOx concentrations may, in embodiments, especially be elevated in the vicinity of a vessel (in case the vessel has NOx emissions). Therefore, an optimum synergy may exist between NOx and methane removal, when the chlorine-comprising compound has a relatively short lifetime, for example emission of a chlorine-comprising compound with less than 1 hour lifetime. However, the maximum emission with short lifetime may be limited by safety limits, and to further increase NOx and methane removal it may be necessary to increase the lifetime and the total emission.

[0053] In the case of ship plume emissions, in embodiments, the emission of the chlorine-comprising compound should preferably not exceed a fraction of the fuel consumption. In embodiments, an acceptable amount of emission may be below 125 g chlorinecomprising compound per kg of fuel consumed, such as below 100 g chlorine-comprisingcompound per kg of fuel consumed, like below 50 g chlorine-comprising compound per kg of fuel consumed, especially below 35 g chlorine-comprising compound per kg of fuel consumed, such as in specific embodiments at least about 2 g chlorine-comprising compound per kg of fuel consumed.

[0054] In embodiments, the vessel may be fueled by a methane-comprising fuel. For example, in embodiments, the vessel may comprise a methane-fueled vessel. Alternatively, in embodiments, the vessel may comprise an LNG-fueled vessel, i.e., the vessel may be fueled by liquified natural gas (which may comprise methane). Hence, in such embodiments, upon execution of the method (i.e., injection of the chlorine-comprising compound), the (gaseous flow especially the) exhaust stream may comprise both the chlorine-comprising compound and the pollutant, here especially at least methane.

[0055] Moreover, in embodiments, the method may comprise producing the chlorinecomprising compound. Especially, in embodiments, the method may further comprise producing the chlorine-comprising compound on board of the vessel. For example, the chlorine-comprising compound may be produced (on-site) using electrolysis techniques. Especially, in embodiments, the chlorine-comprising compound may be produced (on-site) from a salt water comprising starting material using electrolysis techniques, especially seawater electrochlorination. In embodiments, the salt water comprising starting material may be selected from the group comprising sea water and brine. The use of a brine as a starting material may especially be beneficial over sea water, because electrochlorination of sea water may (i) require special equipment which is not the case for a brine, and (ii) have a risk of biological fouling, which risk is lower when using a brine. Moreover, since salt is relatively cheap and readily available in sufficient purities, the use of a brine (i.e., a concentrated salt water solution) the electrolysis may be facile and cost efficient. Additionally, the electrolysis process may also yield hydrogen gas, which may be used as a sustainable fuel. Finally, renewable energy sources such as wind power, solar power, wave power, hydroelectric power, and geothermal power may be used for powering the electrochlorination, therewith making the method even more climate beneficial. In addition to having low carbon intensities, these renewable sources may be applied locally making the installation independent of the power grid, meaning it could be deployed in essentially any location.

[0056] In embodiments, the electrochlorination may comprise feeding filtered (i.e., after removal of solids to protect the equipment) seawater to an electrolysis cell. The electrolysis cell may, in embodiments, comprise anodic and cathodic electrodes, such as electrodes comprising corrosion-resistant materials selected from the group comprising:titanium, stainless steel, copper, bronze, graphite, platinum, nickel, steel or stainless steel, mixed metal oxides (MMO) including ruthenium (RuO2) and iridium (IrO2); and titanium or titanium coated with MMO. In embodiments, a low voltage (especially greater than the theoretical minimum voltage of 0.53 V) may be applied to the electrodes, therewith initiating the electrolysis process. Especially, the low voltage may be selected from the operating range of 2.5-4.5 V, such as from the operating range of 3.0-3.5 V. Such voltages may especially be applied to overcome overpotential of the electrodes, ohmic resistance, bubble formation and other inefficiencies. During the electrolysis process, in general, chlorine ions may be converted into chlorine gas at the anode (2CI — Ch + 2e_), whereas water may be converted into hydrogen gas and hydroxide ions at the cathode (2H2O + 2e — H2 + 2OH ). In embodiments, the chlorine gas produced at the anode may react with water and hydroxide ions to form sodium hypochlorite following the reaction: Ch + 2NaOH — > NaClO + NaCl + H2O. The produced sodium hypochlorite and hydrogen gas may subsequently, in embodiments, be separated and stored for further use. Furthermore, in embodiments, the produced hydrogen gas may be used for energy generation to contribute to the electricity required for further electrochlorination efforts, for example using a hydrogen fuel cell.

[0057] In general, chlorine concentrations in air (e.g. in swimming pools) may be considered safe when remaining below 0.5 ppm (1.5 mg / m3). Thus, in embodiments, the method may further comprise maintaining a maximum chlorine gas (Ch) concentration at a radius of 50 m of the vessel (especially the exhaust of the vessel) (see also further below) of at most 0.5 ppm, especially at most 0.1 ppm, such as at most 0.05 ppm, like at most 0.04 ppm, especially at most 0.02 ppm. The maximum chlorine gas concentration may also, in embodiments, be defined in terms of at most 0.5 ppm within 6 minutes after emission, such as at most 0.25 ppm within 6 minutes after emission, like at most 0.15 ppm within 6 minutes after emission. However, it is noted that the maximum chlorine gas concentration, as defined in such embodiments, may be strongly dependent on (or influenced by) environmental parameters such as wind speed, injection rate, humidity, etc. This dependence may be assessed through an environmental impact assessment. Yet alternatively, in embodiments, the maximum chlorine gas concentration may be defined as at most 0.5 ppm at the point of release (i.e., 0 seconds after emission), which may especially be achieved when the chlorine comprising compound comprises a Ch precursor (i.e. when very little Ch may be present at the initial emission location, because the chlorine-comprising compound has not yet been converted to Ch).

[0058] In embodiments, the method may comprise (installing and) operating a chlorine sensor to detect a (local) chlorine gas concentration in the air. The chlorine sensor may, inembodiments, be configured to provide a sensor signal based on the chlorine concentration. In embodiments, the method may comprise lowering or even shutting down a chlorine-comprising compound production rate or injection rate when the (local) chlorine gas concentration exceeds the maximum chlorine gas concentration. Additionally, in embodiments, the method may comprise maintaining or even increasing a chlorine-comprising compound production rate when the (local) chlorine gas concentration is below the maximum chlorine gas concentration. In embodiments, the chlorine sensor may for example comprise an electrochemical chlorine sensor. Moreover, in embodiments, the chlorine sensor may be configured to calculate the (local) chlorine concentration based on an environmental impact assessment.

[0059] In embodiments, the method may thus comprise injecting the chlorinecomprising compound in the exhaust stream of a target object. As described above, the target object may comprise a vessel. Alternatively, in embodiments, the target object may comprise a structure. For example, in embodiments the target object may comprise an airborne target object, such as for example an aircraft, a balloon, or a zeppelin. Such an airborne target object may, in embodiments, comprise an exhaust device configured to provide an exhaust stream. An advantage of an airborne target object may be that the chlorine-comprising compound may be relatively easily dispersed across a large area from a single target object, as well as being relatively easily dispersed in a targeted manner, i.e., in specific locations. In such embodiments, it may be preferable that the atmospheric lifetime of the chlorine-comprising compound is less than 8 hours, in order to prevent damage to the stratosphere. In embodiments where the target object comprises an airborne target object, such as an aircraft, the method may thus comprise injecting the chlorine-comprising compound in the exhaust stream of the airborne target object.

[0060] Moreover, in embodiments, the target object may comprise a structure selected from the group comprising: an (off-shore) oil platform, a(n off-shore) wind turbine, and a(n onshore) flare stack. Moreover, in embodiments, the target object may comprise a structure selected from a lighthouse, or an artificial or natural island. In embodiments, the structure is not a factory emitting chlorine as pollutant from its industrial activities. The term “structure” may herein refer to a single structure, such as a single wind turbine or a single lighthouse. Alternatively, the term “structure” may also refer to a plurality of structures, or arrangement of structures, such as e.g. a field or arrangement of multiple wind turbines. Moreover, in embodiments, the structure may be or may comprise a flow generating device. For example, in embodiments, the structure may comprise a flare stack, which may function as a flow generating device. In another example, the structure may comprise a wind turbine comprisinga flow generating (and / or injection) device configured to provide a gaseous flow (comprising the chlorine-comprising compound) into the tropospheric space.

[0061] Similarly to the embodiments as described for the vessel, in embodiments, the method may comprise producing the chlorine-comprising compound at the structure. However, this may not necessarily be the case. In embodiments where the chlorine-comprising compound is produced at the structure, it may especially be produced (on-site) from a salt water comprising starting material (such as sea water and / or brine) using electrolysis techniques (especially seawater electrochlorination). For example, in embodiments, the target object may comprise a structure, such as a (plurality of) wind turbine(s) located on land but close to the sea, i.e., in the maritime region as defined herein. The structure may in such embodiments further comprise a chlorine-comprising compound production device, such as a device for electrochlorination. The chlorine-comprising compound production device may especially be configured in a fluid (more especially gaseous) connection with an injection device (see also further below) of the target object. In other words, the chlorine-comprising compound production device may be configured functionally coupled with (the injection device of) the target object. Hence, in embodiments, the method may comprise producing the chlorinecomprising compound at the structure by operation a chlorine-comprising compound production device and fluidically coupling said device with the injection means of the target object to inject the produced chlorine-comprising compound into the gaseous flow. The production of the chlorine-comprising compound at the structure (on-site) may provide synergy with the use of e.g. wind turbines, as the renewable energy sourced from the wind turbines may be used for powering the electrochlorination, therewith making the method even more climate beneficial.

[0062] In addition to having low carbon intensities, these renewable sources may be applied locally making the installation independent of the power grid, meaning it could be deployed in essentially any location. For example, the structure may comprise a(n off-shore or open-ocean) field of wind turbines.

[0063] In specific embodiments, the method may comprise injecting the chlorinecomprising compound in a gaseous flow at a(n off-shore) wind turbine. Hence, in embodiments, the target object may comprise a wind turbine configured to inject the chlorine-comprising compound into a flow of gas in the air as a result of the wind, which may function as the gaseous flow. In such embodiments, the wind turbine may further be configured to generate electricity, which may be used as input for the production of the chlorine-comprising compound. The chlorine-comprising compound may especially, in embodiments, be injected into the gaseous(air) flow (e.g. wind) generated at the top of the wind turbine. As such the chlorine-comprising compound may be produced at relatively low cost, while the height of the wind turbine may be leveraged for release of the chlorine-comprising compound at higher altitudes (such as typically between 80-130 meters). The release at high altitude may help to prevent high Ch concentrations near the surface, therewith (i) improving safety of the method (ii) preventing loss of reactive material through deposition to the surface, and (iii) increasing the volume of gas (especially air) into which the chlorine-comprising compound may be mixed. A further synergy may be that with this embodiment more chlorine-comprising compound (compared to lower altitude release) may be produced during high wind conditions (due to more electricity production), while at the same time higher emissions may also be allowed during high wind conditions (which may dilute the emission leading to lower chlorine concentrations). When the method may be applied on a ship plume, the updraft of warm air from the ship exhaust may help to carry the chlorine-comprising compound to high altitude, but if the method may be applied to remove general pollution from the atmosphere, then the height of the wind turbine may be a great benefit. Release at high altitude may especially be important when using a chlorine-comprising compound that releases Ch indirectly, such as NaOCl, because it may be an advantage to release NaOCl aerosols at high enough altitude to prevent them from depositing into the ocean before they may be converted into Ch.

[0064] Additionally or alternatively, in embodiments, the chlorine-comprising compound may be injected into the gaseous flow by an injection device (spatially) separate from the wind turbine, such as a chimney, that is functionally coupled to the wind turbine. The advantage of this approach may be that renewable electricity from one or more wind turbines may be used to produce and / or inject the chlorine-comprising compound. Additionally, such an injection device may be functionally coupled to a flow generating device (such as e.g. a chimney) configured to generating the gaseous flow into which the chlorine-comprising compound may be injected. Such embodiments may provide the additional benefit that the gaseous flow may be controllable as compared to using (natural) wind as the gaseous flow. In such an embodiment, the target object may thus (i) comprise a structure comprising at least one wind turbine and (ii) be functionally coupled to a (spatially) separate injection device and / or flow generating device, as well as optionally an electrolysis system that is configured to generate the chlorine comprising compound. For example, the method of the invention may be applied in an offshore field of wind turbines that comprises a plurality of wind turbines that feed electricity to an electrolysis unit. In this example, the electrolysis unit may be used to produce the chlorine-comprising compound. Moreover, the electrolysis unit may befunctionally coupled, such as fluidically connected, to the injection device, such that chlorinecomprising compound produced at the electrolysis unit may be transported to and injected into the gaseous flow by the injection device. The wind turbines may, in such embodiments, be configured to inject the chlorine-comprising compound into the gaseous flow (and especially into the tropospheric space). Hence, in embodiments, the wind turbines may comprise or be physically connected to the injection device. Additionally or alternatively, the wind turbine(s) may primarily function as sources of energy, while (i) a (spatially) separate flow generating device, such as e.g. a chimney or release tower, may be configured to generate (or emit) a gaseous flow at an altitude, and (ii) a (spatially) separate injection device may be configured to inject the chlorine-comprising compound into that gaseous flow.

[0065] An important advantage of the use of offshore wind or electrolysis systems may be that offshore wind provides low cost electricity, and that electrolysis may produce chlorine from sea water (which means it is not limited by availability of input materials).

[0066] Herein, the phrase “A functionally coupled B” may especially refer to the elements A and B being configured to co-operate through one or more connections selected from, but not limited to, a fluidic (such as liquid or gas) connection, an electrical connection, a physical connection, a mechanical connection, and an optical connection. For example, referring to above described embodiments, an injection device may be functionally coupled to the electrolysis unit through a fluidic (especially gaseous) connection. A may also be functionally coupled to B in that a sensor signal of a sensor sensing A, or sensing an action of A (or an action associated to A), is used to control B, or an action of B.

[0067] As can be derived from the previous section, environmental factors such as wind speed or e.g. movement speed (of the vessel) may influence the efficiency of the method, as they may influence a level of dilution of the chlorine-comprising compound in the tropospheric space. The term “wind speed” (or wind velocity) may refer to both the velocity and the direction of the wind. Moreover, the term “wind speed” may take into account the movement of the ship relative to (i) the water surface and / or (ii) the surrounding air (ground speed versus wind speed). Therefore, in embodiments, the method may further comprise deriving an environmental parameter from the tropospheric space. In embodiments, the environmental parameter may be selected from one or more of: sunlight (intensity), chlorine gas concentration, humidity, nitrogen oxide concentration, wind speed relative to ship or relative to surface (e.g. at the location of the vessel), and weather conditions. Especially, the method may comprise controlling an injection rate ( ) for injecting the chlorine-comprising compound into the gaseous flow based on the environmental parameter. In this way, optimal conditions can beobtained and with a minimum of energy and materials, a maximum of pollutant may be removed.

[0068] The method may, for example, comprise deriving an environmental parameter from the tropospheric space using one or more sensors. In embodiments, the one or more sensors may be configured to derive an environmental parameter from the tropospheric space and generate a corresponding sensor signal. For example, in embodiments, the method may comprise using a sensor that is configured to detect sunlight (i.e. a solar intensity sensor) to provide a solar intensity signal. Additionally or alternatively, in embodiments, the method may comprise using a sensor that is configured to detect (local) chlorine gas levels to provide a chlorine gas concentration signal. Such embodiments may be beneficial as chlorine concentrations may be kept below concentrations that would be dangerous (e.g. to a crew or wildlife) if the gaseous flow blows to the surface. Additionally or alternatively, in embodiments, the method may comprise using a sensor that is configured to detect (local) NO levels to provide an NOXconcentration signal. Additionally or alternatively, in embodiments, the method may comprise using a sensor that is configured to detect (local) humidity levels to provide a humidity signal. Hence, different types of environmental parameters may be derived using different sensors.

[0069] The one or more sensors may, in embodiments, comprise one or more mobile sensors. A mobile sensor may, for instance, refer to a drone (or unmanned aerial vehicles UAVs) or drone -based sensor. Hence, in embodiments, the one or more sensors may comprise one or more drones or drone-based sensors.

[0070] Furthermore, in embodiments, the method may comprise controlling the injection rate (nj for injecting the chlorine-comprising compound into the gaseous flow in dependence of the sensor signal.

[0071] The method may thus, in embodiments, comprise an open-system approach, i.e., the chlorine-comprising compound may be injected into the open air, where it may be influenced by environmental parameters. In specific embodiments, the step of injecting the chlorine-comprising compound into the gaseous flow may be performed during daytime. Such embodiments may be beneficial as conversion of the chlorine-comprising compound to chlorine radicals may be more efficient in the presence of daylight, therewith preventing buildup of unconverted chlorine-comprising compound and / or chlorine gas (i.e., preventing unsafe environments for crew).

[0072] In another aspect, the invention may provide a pollution removal arrangement configured for removing a pollutant from a tropospheric space. Tn embodiments, the pollutionremoval arrangement may comprise an injection device, a flow generating device, and a control system. The flow generating device may, in specific embodiments, comprise an exhaust device such as a chimney. Especially, in embodiments, the flow generating device may be configured to generate a gaseous flow (especially an exhaust plume) into the tropospheric space. In embodiments, the injection device may especially be configured to inject a chlorine-comprising compound into the gaseous flow. Moreover, in embodiments, the injection device may comprise a chlorine-comprising compound source configured to host the chlorine-comprising compound. In embodiments, the injection device may be fluidically coupled to the flow generating device. Moreover, in embodiments, the chlorine-comprising compound may comprise sodium hypochlorite (NaOCl). Further, in embodiments, the control system may be configured to control an injection rate (n) for injecting the chlorine-comprising compound into the gaseous flow. Hence, in specific embodiments, the invention may provide a pollution removal arrangement configured for removing a pollutant from a tropospheric space, the pollution removal arrangement may comprise an injection device, a flow generating device, and a control system, wherein: (A) the flow generating device (especially an exhaust device such as a chimney) may be configured to generate a gaseous flow (especially an exhaust plume) into the tropospheric space; (B) the injection device (may comprise a chlorine-comprising compound source configured to host a chlorine-comprising compound, wherein the injection device) may be configured to inject a chlorine-comprising compound into the gaseous flow, (wherein the injection device may be fluidically coupled to the flow generating device); wherein the chlorine-comprising compound may comprise sodium hypochlorite (NaOCl); (C) the control system may be configured to control an injection rate (n) for injecting the chlorinecomprising compound into the gaseous flow. The arrangement of the invention may provide the benefit of removing pollutants from the open air. The arrangement may especially be beneficially integrated with existing infrastructures, such as a vessel (like a ship) or a structure (like a wind turbine). The use of NaOCl may especially be preferred, because it has lower environmental impact (for example low impact on atmospheric and ocean acidity) and is relatively safer compared to Ch. Moreover, the arrangement may provide a relatively cheap and easy way to remove even low concentrations of pollutants from a tropospheric space, such as in a maritime region.

[0073] In embodiments, the pollution removal arrangement may thus comprise an injection device. The injection device may especially be configured to inject the chlorinecomprising compound (as defined above for the method) into a gaseous flow. Such injection of the chlorine-comprising compound may, in embodiments, occur at an injection rate ( / - / ).In embodiments, the pollution removal arrangement may be comprised by or configured on or physically attached to the target object. For example, the target object may comprise a vessel comprising an exhaust device which may function as the flow generating device. In such embodiments, the vessel may further comprise an injection device configured functionally coupled, such as fluidically connected, to the exhaust device of the vessel. In an alternative example, the target object may comprise one or more wind turbines. In such embodiments, the wind turbine may comprise an injection device and a flow generating device configured at an altitude (for example in a blade hub, i.e. the central component connecting the rotor blades, of the wind turbine). Alternatively, in such embodiments, the wind turbine may be functionally coupled to a (spatially) separate pollution removal arrangement comprising an injection device and a flow generating device (such as e.g. a chimney).

[0074] The gaseous flow may furthermore be provided into the tropospheric space. Therefore, in embodiments, the flow generating device may be configured to generate a gaseous flow into the tropospheric space. For example, in embodiments, the flow generating device may comprise an exhaust device such as a chimney. Especially, in embodiments, (the flow generating device, especially) the exhaust device may comprise an exhaust of a combustion engine such as e.g. of a vessel. Alternatively, in embodiments, the flow generating device may comprise a wind turbine, i.e., the flow generating device may leverage local wind conditions to provide the gaseous flow. Regardless of what type of flow generating device, in embodiments, the injection device may be fluidically coupled to the flow generating device.

[0075] Similarly to the embodiments described for the method of the invention. In embodiments, the chlorine-comprising compound may comprise (direct) chlorine gas or a(n indirect) precursor of chlorine gas. Especially, in embodiments, the chlorine-comprising compound may comprise sodium hypochlorite (NaOCl). Sodium hypochlorite may, in embodiments, be aerosolized. Especially, in such embodiments, the aerosolized sodium hypochlorite may be converted to Ch when it is mixed with acids (such as HC1, see also further below) in the atmosphere. An advantage of such embodiments may be that NaOCl emissions generally may not increase the acidity of the atmosphere and the ocean (instead it may have a slight alkaline effect). For Ch and HOC1 emissions, a problem may be that the end result of the reaction chain may typically be two or one HO molecules, respectively, which may increase the acidity of the atmosphere or the ocean (where the HC1 will deposit). The use of NaOCl as the chlorine-comprising compound may overcome this problem. NaOCl itself may be slightly alkaline (in water it forms NaOH - a strong base, and HOC1 - a weak acid), and the reaction chain starting with a reaction of NaOCl+2HCl— >Ch+NaCl+FhO may consume two HC1molecules (a strong acid), and then produce two new HC1 molecules (Ch eventually leading to two HC1 molecules). Thus, following the reaction chain the number of acid molecules in the atmosphere and ocean may not change with the emission of NaOCl, which may be a great advantage in view of environmental impact.

[0076] Another advantage of embodiments where the chlorine-comprising compound comprises NaOCl may be that such a method may be relatively safe compared to direct emission of Ch gas. Through the use of NaOCl, chlorine gas concentrations close to the target object may be at least lOx lower, therewith protecting the crew and the environment around the ship against high Ch emissions. Furthermore, the use of NaOCl as the chlorine-comprising compound may provide the benefit of adjustability of the lifetime of the compound through its particle size, which may be changed by changing the dilution of the compound. Smaller NaOCl aerosols may have a relatively higher surface area, due to which they can take up relatively more HC1 for the same HC1 background concentration. For a given particle size, if the dilution is higher (less NaOCl per volume), then the total number of aerosols may be increased for the same amount of NaOCl, again resulting in a higher surface area density and therefore a higher uptake of HC1.

[0077] Additionally or alternatively, in embodiments, the chlorine-comprising compound may comprise another compound configured to (indirectly) release CI2 into the air, such as an inorganic chloride selected from the group comprising: a hypochlorite other than sodium hypochlorite (such as Ca(OCl)2, LiOCl, and KOC1), chlorites (such as NaCICh. Mg(ClO2)2, and KCIO2), chlorates (such as NaCICh, and KCIO3), and hypochlorous acid (HC1O). The hypochlorites may especially be converted to CI2 when it is mixed with acids (such as HC1, see also further below) in the atmosphere. Conversely, the chlorates may be converted to CI2 (i) under heating and / or (ii) under exposure to strong acids such as HC1. Furthermore, hypochlorous acid (which may be naturally formed in bleach solutions) may readily release chlorine gas after uptake by acidic aerosols in the atmosphere.

[0078] In embodiments, the chlorine-comprising compound may especially be injected into the gaseous flow. Furthermore, in embodiments, the injection device may be configured to inject the chlorine-comprising compound into the gaseous flow during daytime. An advantage of such embodiments may be that photolysis may occur under the influence of sunlight, therewith allowing the chlorine-comprising compound to be converted into chlorine radicals, see also further below.

[0079] The pollution removal arrangement may further, in embodiments, comprise a control system. In embodiments, the control system may especially be configured to controlthe injection rate (r;) of the chlorine-comprising compound. Therefore, in embodiments, the pollution removal arrangement may further comprise one or more sensors. The one or more sensors may, in embodiments, be configured to derive an environmental parameter from the tropospheric space and generate a corresponding sensor signal. Especially, in embodiments, the environmental parameter may be selected from one or more of: sunlight (intensity), chlorine gas concentration, humidity, nitrogen oxide concentration, wind speed, and weather conditions. For example, in embodiments, the pollution removal arrangement may comprise a sensor that is configured to detect sunlight (i.e. a solar intensity sensor). Such as sensor may especially be useful to provide the environmental parameter of sunlight (intensity), based on which the control system may be configured to turn on or turn off the emission (or injection) of the chlorine-comprising compound into the gaseous flow. Additionally or alternatively, in embodiments, the pollution removal arrangement may comprise a sensor that is configured to detect (local) chlorine gas levels. Such embodiments may be beneficial as chlorine concentrations may be kept below concentrations that would be dangerous (e.g. to a crew or wildlife) if the gaseous flow blows to the surface. Additionally or alternatively, in embodiments, the pollution removal arrangement may comprise a sensor that is configured to detect (local) NOx levels. Additionally or alternatively, in embodiments, the pollution removal arrangement may comprise a sensor that is configured to detect (local) humidity levels.

[0080] In embodiments, the pollution removal arrangement may further comprise sensor unit configured to quantify pollutant removal by the pollution removal arrangement (using the chlorine-comprising compound). The sensor unit may comprise an outlet configured downstream of the injection device. The outlet may be configured to provide a fluid connection between a sensor reactor of the sensor unit, and the injection device. Further, the sensor unit may thus comprise a sensor reactor configured functionally coupled to the outlet to receive a sample of the gaseous flow comprising the chlorine-comprising compound. The sensor reactor may, in embodiments, comprise one or more radiation devices (such as one or more light sources) configured to provide first radiation (or first source light). In embodiments, the first radiation may have a wavelength selected such that precursors to chlorine radicals in the chlorine-comprising compound may be activated to generate chlorine radicals. These chlorine radicals may especially react with the pollutant in the sample of the gaseous flow. A change of concentration of pollutant prior to and after irradiation with the first radiation may indicate the amount of pollutant removal. In embodiments, the first radiation may have a wavelength selected from the (UV) wavelength range of 100-540 nm, such as from the wavelength range of 180-400 nm. Hence, in embodiments, the sensor unit may comprise a photoreactor or maybe a photoreactor-based sensor unit. Further, in embodiments, the sensor unit may comprise a first pollutant sensor configured upstream of the sensor reactor and a second pollutant sensor configured downstream of the sensor reactor. The pollutant sensors may for example, in embodiments, comprise methane concentration sensors. In embodiments, the sensor reactor may be configured to activate the precursors to chlorine radicals, i.e., the chlorine-comprising compound, and therewith initiate pollutant oxidation in the sample of the gaseous flow (e.g. exhaust gas). The pollutant removal may especially be quantified by comparing the measurement of the first and second pollutant sensors. For example, the first pollutant sensor may measure a pollutant concentration that may be 10% of the measurement by the second pollutant sensor, which means that 90% of the pollutant was removed. The pollutant removal quantification by the sensor may then be used to evaluate the total pollutant removal by the pollution removal arrangement. For example, if the sample directed to the sensor was 1% of the total flow, then the total pollutant removal may be 100 times the removal as quantified by the sensor.

[0081] Further, in embodiments, the residence time of the chlorine-comprising compound in the reactor may be more than 5 times shorter, such as more than 10 times shorter, like more than 15 times shorter than the residence time of the chlorine-comprising compound in the tropospheric space. Yet further, in embodiments, the residence time of the chlorinecomprising compound in the reactor may be more than 30 times shorter, such as more than 45 times shorter, like more than 60 times shorter than the residence time of the chlorinecomprising compound in the tropospheric space. In addition, UV lights in the reactor may be substantially stronger than solar intensity in the tropospheric space. As a result, quantification using the herein described sensor unit may be relatively rapid. A short residence time may be especially advantageous in combination with Ch as chlorine-comprising compound, because Ch may be relatively rapidly photolyzed using UV lights. Alternatively, in embodiments, the residence time of the chlorine-comprising compound in the reactor may be similar to the residence time of the chlorine-comprising compound in the tropospheric space. Such embodiments may be advantageous to provide a highly accurate quantification. Furthermore, such embodiments may be beneficial in combination with for Ch precursors such as NaOCl aerosols as chlorine-comprising compound, because NaOCl lifetime may not only depend on UV light intensity, but also on its reaction with acids.

[0082] Further, in embodiments, the amount of chlorine-comprising compound present in the gaseous flow may be greater than the available pollutant in the sample. This may for example be the case when the pollutant may be present in the tropospheric space and may needto be mixed with the chlorine-comprising compound after release thereof to the tropospheric space. To address this, the sensor reactor may comprise an additional inlet to inject additional pollutant-comprising gas into the sensor reactor. For example, the inlet might inject a sample of tropospheric air, or the inlet might inject pollutant from another pollutant source (for example a gas cylinder with pollutant gas might be used). In this way the sensor unit may be used to evaluate the total pollutant removal potential of the chlorine-comprising compound. Furthermore, in embodiments, the inlet may be configured to inject an acid (such as e.g. HC1) into the sensor reactor to accelerate the conversion of a Ch precursor like NaOCl into Ch. As such the residence time of the chlorine-comprising compound in the sensor reactor may be reduced.

[0083] Furthermore, in embodiments, the control system may be configured to control the injection rate (n) for injecting the chlorine-comprising compound into the gaseous flow. Especially, in such embodiments, the control system may be configured to control the injection rate (n) for injecting the chlorine-comprising compound into the gaseous flow in dependence of the sensor signal. Additionally or alternatively, in embodiments, the control system may be configured to control the injection rate (n) for injecting the chlorine-comprising compound into the gaseous flow in dependence of the quantification of pollutant removal by the (photoreactorbased) sensor unit. Furthermore, in embodiments, the control system may (also) be configured to control the injection rate (n) in dependence of data relating to the target object with which the pollution removal arrangement may be integrated (such as e.g. a vessel like a ship). Especially, in such embodiments, the data relating to the target object may comprise one or more selected from the group comprising: cruise speed, wind speed (and therewith dispersion rate), local weather, meteorological and air quality information. Use of one or more sensors may advantageously help improve the methane removal performance of the arrangement, e.g. by detecting (i) when there is sunlight to photolyze chlorine gas (e.g. measured with a UV photodetector), and (ii) when there is no rain or fog which would unwantedly remove chlorinecomprising compound from the atmosphere by wet deposition (e.g. measured with a humidity sensor), and (iii) when the relative wind speed may increase such that extra chlorine-comprising compound may be emitted without going over the safety levels (e.g. measured by a wind speed sensor), (iv) how much sea spray aerosol may be present (e.g. measured with a particulate matter sensor), (v) how much mineral dust may be present (e.g. measured with a particulate matter sensor), and (vi) what pollutants, such as e.g. NOx, Ch and VOCs may be present.The system may thus, in embodiments, comprise an open-system, i.e., the chlorine-comprising compound may be injected into the open air, where it may be influenced by environmental parameters.

[0084] Further, in embodiments, the pollution removal arrangement may further comprise a chlorine-comprising compound production device. Embodiments of the chlorinecomprising compound production device have been further described above. In particular, in embodiments, the chlorine-comprising compound production device may be configured to (onsite) convert a salt water starting material (such as sea water and / or brine) into the chlorinecomprising compound using electrolysis techniques (especially seawater electrochlorination). In further embodiments, the chlorine-comprising compound production device may be functionally coupled to the chlorine-comprising compound source as defined above.

[0085] The pollution removal arrangement may further, in embodiments, comprise a UV reactor. In embodiments, the UV reactor may comprise one or more radiation devices configured to provide first radiation. The first radiation may, in embodiments, have a wavelength selected from the (UV) wavelength range of 180-540 nm, such as from the wavelength range of 200-500 nm, like from the range of 300-400 nm. Especially, in embodiments, the first radiation may be provided to the flow generating device. As such, in embodiments, the UV reactor may be configured to operate during a (local) absence of sunlight in the tropospheric space. Hence, in embodiments, the pollution removal arrangement may further comprise a UV reactor, wherein the UV reactor may comprise one or more radiation devices configured to provide first radiation, wherein the first radiation may have a wavelength selected from the (UV) wavelength range of 180-540 nm; and wherein the first radiation may be provided to the flow generating device. Such embodiments may be beneficial as the first radiation may provide the benefit of initiating photolysis even in the absence of sunlight, e.g. during the nighttime. Especially, the UV reactor may initiate photolysis prior to the gaseous flow being provided in (such as released or emitted into) the tropospheric space, e.g. within a chimney of an exhaust device. As such, a local concentration of chlorine radicals in the UV reactor may be increased, therewith increasing the efficiency of methane removal near the target object. Such embodiments may be beneficial as usually during nighttime no pollutants may be removed by releasing the chlorine-comprising compound to the atmosphere due to the deficiency of an initiator (like sunlight) for photolysis.

[0086] In embodiments, the pollution removal arrangement may further comprise a filter configured in the flow generating device. Alternatively, in embodiments, the filter may be configured downstream of the flow generating device, especially outside of the UV reactor.The filter may especially, in embodiments, be configured to filter out HC1 from the gaseous flow. The terms “upstream” and “downstream” relate to an arrangement of items or features relative to the propagation of the gaseous flow from a gaseous flow generating means (here especially the target object, more especially a combustion engine), wherein relative to a first position within the gaseous flow, a second position in the gaseous flow closer to the gaseous flow generating means generating means is “upstream”, and a third position within the gaseous flow further away from the gaseous flow generating means is “downstream”.

[0087] Moreover, the pollution removal arrangement may, in embodiments, further comprise a CCh-capturc device. Such a CCh-capturc device may especially be advantageous if the target object uses a methane-comprising fuel, because methane slip may not be captured using a CCh-capture device, and thus the method of the invention may provide a solution for methane removal combined with CO2 capturing. In embodiments, the CCh-capturc device may be configured to remove CO2 from the gaseous flow. Especially, in embodiments, the CO2-capture device may be configured to remove CO2 prior to the injection of the chlorinecomprising compound into the gaseous flow. Removing the CO2 prior to injection of the chlorine-comprising compound may be desirable to ensure that the chlorine-comprising compound does not affect the CO2 capturing performance and to ensure the chlorinecomprising compound is not lost (captured) in the CCh-capturedevice. Therefore, in embodiments, the CCh-capture device may be configured upstream of an injection site of the injection device in the gaseous flow. The CCh-capture device may especially be configured to remove CO2 using post-combustion carbon capture technology. Hence, in specific embodiments, the pollution removal arrangement may further comprise a CCh-capture device, wherein the CCh-capture device may be configured to remove CO2 from the gaseous flow using post-combustion carbon capture technology.

[0088] In embodiments, the CCh-capture device may comprise a pre-processing reactor, an absorption column, a stripper column and a post-processing reactor. The CCh-capture device may thus be configured to apply post-combustion carbon capture technology. Such postcombustion carbon capture technology may, in embodiments, comprise (a flue gas preparation stage of) lowering the temperature of the gaseous flow by contacting, in the pre-processing reactor, the gaseous flow with (sea)water. As such, in embodiments, the temperature of the gaseous flow may be lowered (or reduced) to a temperature selected from the range of 35-70 °C, such as selected from the range of 40-60 °C, like selected from the range of 40-50 °C. Additionally, in embodiments, the post-combustion carbon capture technology may comprise (an absorption stage of) absorbing CO2 from the low temperature gaseous flow onto a chemicalsolvent configured in the adsorption column. In further embodiments, the post-combustion carbon capture technology may comprise (a desorption stage of) desorbing the captured CO2 by heating the CCh-enriched chemical solvent in the stripper column. Especially, in embodiments, the temperature of the CCh-enriched chemical solvent may be heated (or raised) to a temperature selected from the range of 100-140 °C, such as from the range of 110-130 °C, like from the range of 115-125 °C. Moreover, in embodiments, the post-combustion carbon capture technology may comprise (a CO2 processing stage of) drying and liquefying the captured CO2 in the post-processing reactor (for storage purposes). Yet additionally, in embodiments, the post-combustion carbon capture technology may comprise (a solvent regeneration stage of) regenerating the chemical solvent (e.g. through cooling thereof).

[0089] In another aspect, the invention may provide a target object comprising the pollution removal arrangement as described herein. Additionally or alternatively, in embodiments, the target object may be configured to execute the method as described herein. The target object of the invention may provide the benefit of providing a relatively cheap, safe, and easily integrated system for removing pollution from the atmosphere, especially from the tropospheric space defined above the maritime region.

[0090] In specific embodiments, the target object may comprise a vessel. Especially, in embodiments, the vessel may be selected from the group comprising: a ship, a barge, a yacht, an oiler, a buoy, and a tanker. Moreover, in embodiments, the target object may be configured to generate the gaseous flow (during movement of the target object). Therefore, in embodiments, the target object may comprise a flow generating device as described above. Further, in embodiments, the target object (especially the flow generating device) may comprise an exhaust device (such as a chimney) configured to generate an exhaust stream. In such embodiments, the gaseous flow may comprise the exhaust stream.

[0091] Alternatively, in embodiments, the target object may comprise a structure. In such embodiments, the structure may be selected from the group comprising: an (off-shore) oil platform, a(n off-shore) wind turbine, and a(n on-shore) flare stack.

[0092] In embodiments, the pollution removal arrangement may comprise a chimney or an exhaust stack. For example, in embodiments, the target object may comprise a structure such as an (off-shore) oil platform and the pollution removal arrangement may comprise a flow generating device such as a chimney functionally coupled to the (off-shore) oil platform.

[0093] In specific embodiments, the target object may comprise a(n off-shore) wind turbine integrated with the pollution removal arrangement as described herein. Hence, in embodiments, the target object may comprise a wind turbine configured to produce a gaseousstream, i.e., a flow of gas in the air. Alternatively, in embodiments, the target object may comprise a wind turbine configured to inject the chlorine-comprising compound into an existing gaseous flow, such as e.g. a gaseous flow produced by the wind or by a flow generating device from the pollution removal arrangement. In such embodiments, the wind turbine may be configured to generate electricity, which may be used as input for the production of the chlorine-comprising compound. The chlorine-comprising compound may especially, in embodiments, be injected into the air flow generated (or provided) at the upper section of the wind turbine. As such chlorine-comprising compound may be produced at relatively low cost, while the height of the wind turbine may be leveraged for release of the chlorine-comprising compound at higher altitudes (such as typically between 80-130 meters). The release at high altitude may help to prevent high Ch concentrations near the surface, therewith improving safety of the integrated system comprising the wind turbine and the pollution removal arrangement.

[0094] Alternatively, in specific embodiments, the target object may comprise a vessel like a ship, such that the chlorine-comprising compound may be injected into a ship plume. In such embodiments, the updraft of warm air from the ship exhaust may help to carry the chlorine-comprising compound to high altitude. Release of the chlorine-comprising compound at high altitude may especially be important when using a chlorine-comprising compound that releases Ch indirectly, such as NaOCl, because it may be an advantage to release NaOCl aerosols at high enough altitude to prevent them from depositing into the ocean before they may be converted into Ch. Moreover, in embodiments, the exhaust of the vessel (especially ship plume) may include NOx emission, which may be beneficial for the removal efficiency of methane through the chlorine-comprising compound.

[0095] The chlorine-comprising compound may, in embodiments, be injected into the gaseous flow through aerosols. Therefore, in embodiments, the pollution removal arrangement may comprise an aerosol generator. The aerosol generator may be configured for generating aerosols comprising the chlorine-comprising compound. An aerosol generator may for example comprise a nozzle through which the chlorine comprising compound may be pushed under high pressure, such that it may generate small aerosol droplets. Especially, the chlorine-comprising compound may be injected into the gaseous flow (provided by the flow generating device) as aerosol particles (by the injection device). Additionally or alternatively, in embodiments, the gaseous flow (e.g. wind) may be directed through the aerosol generator, i.e., the gaseous flow may enter an inlet of the aerosol generator where the chlorine-comprising compound may be injected therein, and the gaseous flow may exit through an outlet as a gaseous flow comprisingthe (aerosolized) chlorine-comprising compound. Hence, in such embodiments, the aeorosol generator may comprise the flow generating device and the injection device. Therefore, in embodiments, the injection device may comprise an aerosol generator. Furthermore, the injection device (comprising the aerosol generator) may be configured in fluid connection with the flow generating device, such that the chlorine-comprising compound may be injected into the gaseous flow as aerosol particles. The aerosol particles may, in embodiments, have particle sizes selected from the range of 0.01-10 pm, such as selected from the range of 0.05-5pm, like from the range of 0.1-2 pm. Herein, the particle sizes of aerosols may be defined based on electrical mobility-based sizing techniques, such as using a scanning mobility particle sizer with a differential mobility analyzer.

[0096] In a further embodiment the pollution removal arrangement may be applied for methane removal at oil and gas extraction, including integrated with one or more of: an oil drilling platform, an oil drilling structure onshore in a maritime environment, a gas extraction structure (to reduce harmful leaks or venting), and fracking field (to reduce leaks of natural gas).

[0097] Gas may commonly be pumped along with crude oil and an aqueous solution (brine, etc.), comprising a mixture of methane, carbon dioxide, hydrogen sulfide and other species including salts, dissolved gases, gas bubbles, oil and solids. At some locations the gas may be a waste and may be vented to the atmosphere, and at some of these installations the hydrocarbons may be destroyed by flaring (using a flare stack). However, due to the poor reactivity of methane, a significant portion of methane may pass through the flare without being destroyed (i.e., methane may slip). By integrating the pollution removal arrangement with target objects as described herein, the chlorine-comprising compound may be released from the target object (such as e.g. from a boom or tower where the flaring takes place). Hence, such integrated systems may provide the benefit of reducing methane-slip and / or removing other pollutants from the air.

[0098] In another aspect, the invention may provide an arrangement of the target object and the pollution removal arrangement as described herein, wherein the target object may comprise a structure; and wherein the structure may be selected from the group comprising: an oil platform, a wind turbine, and a flare stack. In embodiments, the target object, especially the structure, and the pollution removal arrangement may thus be separate elements. In such embodiments, the structure may be functionally coupled to the pollution removal arrangement such that the structure may provide electricity to the pollution removal arrangement. Alternatively, in embodiments, the target object, especially the structure, and the pollutionremoval arrangement may be physically interconnected. In other words, the pollution removal arrangement may essentially comprise the target object. For instance, in embodiments, the structure (e.g. a wind turbine) may essentially be the flow generating device and / or the injection device of the pollution removal arrangement.

[0099] Further, in embodiments, the arrangement may comprise a chlorine-comprising compound production device, such as a device for electrochlorination. The chlorine-comprising compound production device may especially be configured in a fluid (more especially gaseous) connection with an injection device (see also further below) of the target object. In other words, the chlorine-comprising compound production device may be configured functionally coupled with (the injection device of) the target object. As such, the arrangement may, in embodiments, be configured to produce the chlorine-comprising compound at (or in the vicinity of) the target object. In embodiments, the chlorine-comprising compound production device may especially be configured to produce the chlorine-comprising compound (on-site) from a salt water comprising starting material (such as sea water and / or brine) using electrolysis techniques (especially seawater electrochlorination).

[0100] In another aspect, the invention may provide a method for functionally coupling a pollution removal arrangement as described herein to a target object as described herein. The method may especially comprise functionally coupling an injection device and a control system (of the pollution removal arrangement) to the target object. Functionally coupling the injection device to the target object may for example refer to providing a fluid (especially gas) connection between the injection device of the pollution removal arrangement and the flow generating device (e.g. the exhaust device) of the target object to facilitate injection of the chlorine-comprising compound into the gaseous flow. Hence, in such embodiments, the target object (e.g. a (methane-fueled) vessel) and the pollution removal arrangement may be physically interconnected. Further, functionally coupling the control system (of the pollution removal arrangement) to the target object may for example refer to providing a fluid (especially gas) connection between a sensor of the control system and the flow generating device (e.g. exhaust device) of the target object to facilitate sensing and measurement of chlorine-levels in the gaseous flow (and in the vicinity of the target object). Additionally or alternatively, functionally coupling the control system (of the pollution removal arrangement) to the target object may for example refer to providing an electrical connection between the control system (of the pollution removal arrangement) to the target object to facilitate control over e.g. the injection rate of the chlorine-comprising compound into the gaseous flow.In embodiments, the target object may not comprise a flow generating device. In such embodiments, the method may further optionally comprise also functionally coupling a flow generating device to the target object. For example, in embodiments, the method may comprise functionally coupling (such as electrically and / or fluidically connecting) a chimney (as flow generating device) to a lighthouse (or wind turbine) (as target object(s)).

[0101] Yet further, in embodiments, the method may comprise also functionally coupling a chlorine-comprising compound production device to the target object. For example, in embodiments, the method may comprise functionally coupling (such as fluidically connecting) an electrolysis unit (as chlorine-comprising compound production device) to an injection device of the target object(s).

[0102] In yet another aspect, the invention may provide a use of the arrangement as described herein for removing (or reducing) methane slip of a target object as described herein in a tropospheric space.

[0103] In yet another aspect, the invention may provide a computer program product comprising instructions for execution on a control system. The control system may especially be configured functionally coupled to the pollution removal arrangement as defined herein, or may comprised thereby. As such, in embodiments, the instructions (comprised by the computer program product), when executed by the control system, may cause the pollution removal arrangement to carry out the method as defined herein. Hence, in specific embodiments, the invention may provide a computer program product comprising instructions for execution on a control system functionally coupled to the pollution removal arrangement system as defined herein, or comprised thereby, wherein the instructions, when executed by the control system, may cause the pollution removal arrangement carry out the method of the invention.

[0104] BRIEF DESCRIPTION OF THE DRAWINGS

[0105] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which: Figs. 1-3 schematically depict embodiments of the invention. The schematic drawings are not necessarily to scale.

[0106] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0107] Figs. 1 A-B schematically depict embodiments of the method of the invention. In specific embodiments as depicted in Fig. 1 A, the invention provides a method for removing a pollutant 5 from a tropospheric space 500. Moreover, in embodiments, the method maycomprise injecting a chlorine-comprising compound 1 into a gaseous flow 50. In further embodiments, the gaseous flow 50 (comprising the chlorine-comprising compound 1) may be provided in (such as released or emitted into) the tropospheric space 500 during daytime. Especially, one or more of (a) the gaseous flow 50 and (b) the tropospheric space 500 may comprise the pollutant 5. Furthermore, in embodiments, the chlorine-comprising compound 1 may comprise sodium hypochlorite (NaOCl). Especially, the method may comprise allowing the pollutant 5 to react (in the tropospheric space 500) with (especially be oxidized by) the chlorine radicals 2 produced from the chlorine-comprising compound 1.

[0108] Further, in embodiments, the chlorine-comprising compound 1 may further comprise an inorganic chloride selected from the group comprising: a hypochlorite other than sodium hypochlorite (such as Ca(OCl)2, LiOCl, and KOC1), chlorites (such as NaCIO:. Mg(C102)2, and KCIO2), chlorates (such as NaCIOv and KCIO3), and hypochlorous acid (HC1O).

[0109] Furthermore, in embodiments, the tropospheric space 500 may be defined as a space (or volume) defined at a height (hi) above a sea surface, an ocean surface, or above a virtual plane Vp at land at sea-level. Moreover, in embodiments, the height (hi) may be selected from the range of 0.5-4 km (such as from the range of 1-3 km, such as about 2 km).

[0110] Furthermore, in embodiments, the tropospheric space 500 may be in a maritime region, defined as (a) above the sea surface, (b) above the ocean surface, or (c) above the virtual plane Vp at land at 0 m height but within a shortest distance di (see Fig. 2B) of 2 km from an ocean or a sea.

[0111] Further, in embodiments, the chlorine-comprising compound 1 may have an atmospheric lifetime (in the tropospheric space 500) of less than 8 hours (during daytime). Moreover, in embodiments, the chlorine-comprising compound 1 may have an atmospheric lifetime in the tropospheric space 500 of at least 30 minutes; (ii) less than 8 hours (during daytime). Especially, the chlorine-comprising compound 1 may be a precursor for chlorine radicals 2, optionally via chlorine gas 3, under atmospheric conditions (in the tropospheric space 500).

[0112] Furthermore, in embodiments, the gaseous flow 50 may comprise one or more of (i) an acid and (ii) an acid precursor, especially in a concentration of at least 50 ppt. In further embodiments, the one or more of an acid and an acid precursor may be selected from the group comprising: HC1, HNO3, H2SO4, SO2, NO2, and HCOOH. Furthermore, in embodiments, the tropospheric space 500 may comprise one or more of (i) an acid and (ii) an acid precursor, especially in a concentration of at least 50 ppt. In further embodiments, the one or more of anacid and an acid precursor may be selected from the group comprising: HC1, HNO3, H2SO4, SO2, NO2, and HCOOH.

[0113] In further embodiments, the pollutant 5 may comprise one or more of the group comprising: methane, a volatile organic compound (VOC), ozone, and nitrogen oxides (i.e., NOx which may comprise NO, NO2, and NO3). Especially, the pollutant 5 may comprise methane.

[0114] Especially, the gaseous flow 50 may comprise an exhaust stream (or plume) 90 of a target object 400. In further embodiments, the exhaust stream 90 may comprise the pollutant 5. In further embodiments, the exhaust stream 90 does not may comprise the pollutant 5. Moreover, in embodiments, the pollutant 5 may be atmospherically present in the tropospheric space 500.

[0115] In further embodiments, the target object 400 may comprise a vessel 410. Moreover, in embodiments, the vessel 410 may be selected from the group comprising: a ship, a barge, a yacht, an oiler, a buoy, and a tanker, see e.g. also Fig. 2A. Especially, Fig. 2A schematically depicts a vessel 410 comprising an exhaust device 250 (such as a chimney 40) configured to provide the exhaust stream 90. Furthermore, in embodiments, the vessel 410 may be fueled by a methane-comprising fuel.

[0116] Especially, the method may further comprise producing the chlorine-comprising compound 1 on board of the vessel 410. Moreover, in embodiments, the target object 400 may comprise a structure 420. The structure 420 may herein refer to a single structure 420, such as a single wind turbine 425 (configured in the maritime region) as depicted in Fig. 2B. Alternatively, the structure 420 may refer to multiple structures 420, such as an arrangement of structures 420. Furthermore, in embodiments, the structure 420 may be selected from the group comprising: an (off-shore) oil platform, a(n off-shore) wind turbine 425, and a(n on-shore) flare stack, see e.g. also Fig. 2B.

[0117] Further, in embodiments, the method may further comprise producing the chlorine-comprising compound 1 at the structure 420. Further, in embodiments, the chlorinecomprising compound 1 may be produced (on-site) from a salt water comprising starting material (such as sea water and / or brine) using electrolysis techniques (especially seawater electrochlorination).

[0118] In further embodiments, the method may further comprise maintaining a maximum chlorine gas (CI2) concentration within a radius of 50 m of the vessel 410 of at most 0.05 ppm. Moreover, in embodiments, the method may comprise deriving an environmental parameter from the tropospheric space 500. Furthermore, in embodiments, the environmentalparameter may be selected from one or more of: sunlight (intensity), chlorine gas concentration, humidity, nitrogen oxide concentration, wind speed, and weather conditions. Furthermore, in embodiments, the method may comprise controlling an injection rate ( j for injecting the chlorine-comprising compound 1 into the gaseous flow 50 based on the environmental parameter.

[0119] Furthermore, in embodiments, the step of injecting the chlorine-comprising compound 1 into the gaseous flow 50 may be performed during daytime.

[0120] With reference to Fig. 1A, in specific embodiments, the invention provides a pollution removal arrangement 1000 configured for removing a pollutant 5 from a tropospheric space 500, the pollution removal arrangement 1000 comprising an injection device 100, a flow generating device 200, and a control system 300. In further embodiments, the flow generating device 200 (especially an exhaust device 250 such as a chimney 40) may be configured to generate a gaseous flow 50 (especially an exhaust plume) into the tropospheric space 500. Further, in embodiments, the injection device 100 may comprise a chlorine-comprising compound source 30 configured to host a chlorine-comprising compound 1. Moreover, in embodiments, the injection device 100 may be configured to inject a chlorine-comprising compound 1 into the gaseous flow 50, (wherein the injection device 100 may be fluidically coupled to the flow generating device 200). Additionally or alternatively, in embodiments, the injection device 100 and the flow generating device 200 may comprise essentially the same element, i.e., the injection device may be configured to generate the gaseous flow 50 (e.g. in the case of a structure 420 such as a wind turbine 425, see also further below). In further embodiments, the chlorine-comprising compound 1 may comprise sodium hypochlorite (NaOCl). Further, in embodiments, the control system 300 may be configured to control an injection rate (ri) for injecting the chlorine-comprising compound 1 into the gaseous flow 50.

[0121] Furthermore, in embodiments, the pollution removal arrangement 1000 may further comprise one or more sensors 310 configured to derive an environmental parameter from the tropospheric space 500 and generate a corresponding sensor signal. Furthermore, in embodiments, the environmental parameter may be selected from one or more of: sunlight (intensity), chlorine gas concentration, humidity, nitrogen oxide concentration, wind speed, and weather conditions. Further, in embodiments, the control system 300 may be configured to control the injection rate (n) in dependence of the sensor signal.

[0122] Fig. IB schematically depicts an embodiment of the pollution removal arrangement 1000 further comprising a sensor unit 900 configured to quantify pollutant 5 removal by the pollution removal arrangement 1000 (using the chlorine-comprising compound1). The sensor unit 900 may comprise an outlet 909, a sensor reactor 950, a first pollutant sensor 910 and a second pollutant sensor 920. The outlet 909 may be configured downstream of the injection device 100, such that the sensor unit 900 may be configured to receive part of (especially a sample of) the gaseous flow 50 comprising the chlorine-comprising compound 1. The sensor reactor 950 may be fluidically connected to the outlet 909. As such, the sensor reactor 950 may be configured to receive a sample of the gaseous flow 50 comprising the chlorine-comprising compound 1.

[0123] The sensor reactor 950 may comprise one or more radiation devices (such as one or more light sources) configured to provide first radiation. In embodiments, the first radiation may have a wavelength selected such that the first radiation may (photochemically) activate the chlorine-comprising compound 1, i.e. the precursor to chlorine radicals, to generate chlorine radicals 2. Therefore, in embodiments, the first radiation may have a wavelength selected from the (UV) wavelength range of 180-540 nm. Further, the first pollutant sensor 910 may be configured upstream of the sensor reactor 950, while the second pollutant sensor 920 may be configured downstream of the sensor reactor 950. The pollutant sensors 910 and 920 may for example be methane concentration sensors. In such embodiments, the sensor reactor 950 may be configured to activate the chlorine-comprising compound 1 and initiate pollutant oxidation, by which pollutant removal may be quantified by comparing the measurement of the first pollutant sensor 910 and the second pollutant sensor 920. Hence, in embodiments, the first pollutant sensor 910 and the second pollutant sensor 920 may be configured to measure a pollutant concentration in the sample of the gaseous flow 50.

[0124] For example, second pollutant sensor 920 may measure a pollutant concentration that may be 10% of the measurement of first pollutant sensor 910, which would mean that 90% of the pollutant was removed. The pollutant removal quantification by the sensor 910 may then be used to evaluate the total pollutant removal by the pollution removal arrangement 1000. For example, if a sample directed to the sensor unit 900 is 1% of the total gaseous flow 50, then the total pollutant removal may be 100 times the removal as quantified by the sensor unit 900.

[0125] Further, in some embodiments, the control system 300 may be configured to determine pollutant removal by the pollution removal arrangement 1000 based on a difference between the measurements of the first pollutant sensor 910 and the second pollutant sensor 920. Especially, the pollution removal arrangement 1000 may further comprise a chlorinecomprising compound production device 600. Furthermore, in embodiments, the chlorinecomprising compound production device 600 may be configured to (on-site) convert a saltwater starting material (such as sea water and / or brine) into the chlorine-comprising compound 1 using electrolysis techniques (especially seawater electrochlorination). Furthermore, in embodiments, the chlorine-comprising compound production device 600 may be functionally coupled to the chlorine-comprising compound source 30 as described herein).

[0126] Moreover, in embodiments, the pollution removal arrangement 1000 may further comprise a UV reactor 700 (especially configured downstream of the injection device 100). Furthermore, in embodiments, the UV reactor 700 may comprise one or more radiation devices 710 configured to provide first radiation 711. Moreover, in embodiments, the first radiation 711 may have a wavelength selected from the (UV) wavelength range of 180-540 nm. Moreover, in embodiments, the first radiation 711 may be provided to the flow generating device 200.

[0127] Furthermore, in embodiments, the UV reactor 700 may be configured to operate during a (local) absence of sunlight in the tropospheric space 500.

[0128] Further, in embodiments, the pollution removal arrangement 1000 may further comprise a filter 720 configured to filter out HC1 from the gaseous flow 50, such as a for example a scrubber filter, such as a water scrubber or NaOH scrubber. Further, in embodiments, the filter 720 may be configured in the flow generating device 200. Furthermore, in embodiments, the filter 720 may be configured to operate (only) during operation of the UV reactor 700.

[0129] Referring to also Fig. 3, in embodiments, the pollution removal arrangement 1000 may further comprise a CCh-capturc device 800. Furthermore, in embodiments, the CO2-capture device 800 may be configured to remove CO2 from the gaseous flow 50 (prior to the injection of the chlorine-comprising compound 1 into the gaseous flow 50, i.e., upstream of an injection site 10 of the injection device 100 in the gaseous flow 50) using post-combustion carbon capture technology.

[0130] Furthermore, in embodiments, the CCh-capture device 800 may comprise a preprocessing reactor 810, an absorption column 820, a stripper column 830 and a post-processing reactor 840. Furthermore, in embodiments, the post-combustion carbon capture technology may comprise: lowering the temperature of the gaseous flow 50 by contacting, in the preprocessing reactor 810, the gaseous flow 50 with (sea)water 85 to a temperature selected from the range of 40-50 °C. Moreover, in embodiments, adsorbing CO28 from the low temperature gaseous flow 50 onto a chemical solvent 80 configured in the adsorption column 820. Further, in embodiments, desorbing the captured CO2 8 by heating the CCh-enriched chemical solvent 80 in the stripper column 830 to a temperature selected from the range of 110- 130 °C. In furtherembodiments, drying and liquefying the captured CO28 in the post-processing reactor 840 (for storage purposes). In further embodiments, regenerating the chemical solvent 80.

[0131] In specific embodiments, the invention provides a target object 400 comprising the pollution removal arrangement 1000 as described herein (and configured to execute the method as described herein).

[0132] In further embodiments, the target object 400 may comprise a vessel 410. Furthermore, in embodiments, the vessel 410 may be selected from the group comprising: a ship, a barge, a yacht, an oiler, a buoy, and a tanker. Moreover, in embodiments, the target object 400 may be configured to generate the gaseous flow 50 (during movement of the target object 400). Especially, the target object 400 (especially the flow generating device 200) may comprise an exhaust device 250 (such as a chimney 40) configured to generate an exhaust stream 90. Moreover, in embodiments, the gaseous flow 50 may comprise the exhaust stream 90.

[0133] Fig. 2 A may thus schematically depict an embodiment of the pollution removal arrangement 1000 configured on-board a target object 400, such as a vessel 140. Here, in embodiments, the injection device 100 may be functionally, such as fluidically, coupled to an exhaust device 250 (like a chimney 40) of the vessel 410. Hence, the exhaust device 250 (specially chimney 40) of the vessel 410 may be configured as the flow generating device 200. The exhaust device 250 may especially be configured to provide an exhaust stream 90, which may function as the gaseous flow 50 for the pollution removal arrangement 1000.

[0134] Fig. 2B schematically depicts an embodiment of the pollution removal arrangement 1000 configured on-shore (but within the maritime region) at a structure 420, such as a wind turbine 425. Here, in embodiments, the injection device 100 may be comprised by the structure 420 and may be functionally, such as fluidically, coupled to a flow generating device 200, such as e.g. (a device integrated with) the blades of the wind turbine 425. The blades of the wind turbine 425 may as such provide a flow of gas into a (slightly) different direction relative to (natural) wind captured by the wind turbine 425, which flow may function as the gaseous flow 50 for the pollution removal arrangement 1000.

[0135] Fig. 2B further schematically depicts how the tropospheric space 500 may be in a maritime region. Here, the maritime region may be defined as (a) above the sea surface, (b) above the ocean surface, or (c) above the virtual plane Vp at land at 0 m height but within a shortest distance di of 2 km from an ocean or a sea.

[0136] Fig. 2C schematically depicts an embodiment of the pollution removal arrangement 1000 configured off-shore at a plurality (or arrangement) of structures 420, suchas wind turbines 425, the system comprising (i) one or more wind turbines 425, (ii) a chimney 40 (or exhaust stack) configured to function as a flow generating device 200 and injection device 100, and (iii) a chlorine-comprising compound production device 600. Here, the plurality (or arrangement) of structures 420, such as wind turbines 425, may thus be configured at sea, such as one or more kilometers from the coast. Moreover, in embodiments, the wind turbine 425 may be configured to provide electricity to one or more of (i) the chimney 40 (e.g. for operating the injection device 100 and / or the flow generating device 200), and (ii) the chlorine-comprising compound production device 600. In specific embodiments, the invention provides a computer program product comprising instructions for execution on a control system 300 functionally coupled to the pollution removal arrangement 1000, or comprised thereby. Moreover, in embodiments, the instructions, when executed by the control system 300, cause the pollution removal arrangement 1000 to carry out the method.

[0137] Further, referring (again) to Fig. 1 in embodiments, the invention provides a pollution removal arrangement 1000 for an exhaust stream 90 that is located in a maritime environment. In this embodiment, the exhaust stream 90 is emitted through the (flow generating device 200, such as here a) smoke stack of a (vessel 410, such as here a) ship. The system 1000 may further comprise an injection device 100 for a Cl-comprising compound 1 (in this example a tube that can release the compound into the smoke stack). In this example, the system 1000 includes an adjustable chlorine-comprising compound source 30 of the Cl-comprising compound 1 (for example a flask with Ch gas, or an electrolysis device for producing Ch gas). The system 1000 is configured in such a way that the Cl-comprising compound 1 is only released into the open air during sunlight, for example by opening / operating the chlorinecomprising compound source 30 only during daylight. In this example the injection device 100 is adding the Cl- comprising compound within the smoke stack, but it is also possible to add the Cl- comprising compound immediately after the exit of the smoke stack. Due to the rapid dispersion of the exhaust stream 90 within the air, there will be relatively high concentrations of the Cl- comprising compound in the vicinity of exit of the smoke stack, while the concentrations will be very low further downstream.

[0138] Further, modelling was executed. On the basis thereof: it may be concluded that application of the method in high NOx-conditions (such as e.g. an exhaust of a ship) may result in extremely high efficiencies of methane removal, even in the case of relatively low chlorinecomprising compound concentrations in the gaseous flow. Modelling showed that (a puff with, i.e.) injection of the chlorine-comprising compound to a Cb concentration of 10 ppb or higher may result in efficient CH4 removal, while for (a smaller puff, i.e.,) injection of the chlorine-comprising compound to a Ch concentration of 1 ppb or lower, the NOx concentration may become relevant to achieve similarly or even higher methane removal efficiencies compared to the high Cb concentration. The effect was observed when using chlorine gas as the chlorinecomprising compound as well as when using sodium hypochlorite as the chlorine-comprising compound.

[0139] Moreover, from the modelling it was observed that use of sodium hypochlorite (with an atmospheric lifetime of 1 hour, 3 hours, and 8 hours) as the chlorine -comprising compound injected into a ship plume led to lower peak Ch concentrations compared to (directly injecting) chlorine gas (Ch) into the ship plume. For modelling of each type of chlorinecomprising compound, an (emission rate or) injection speed of 2.6 g / s chlorine-comprising compound was applied.

[0140] Modelling case 1 - methane removal from a ships’ methane slip The method of the invention may be used to address ambient methane concentrations, but may also be used to address exhaust streams that include methane pollution, such as methane slip by a ship engine, or to address non-methane VOCs. As methane slip can be very high, a relatively high emission of the chlorine-comprising compound may be desired to remove all the methane, preferably using a chlorine-comprising compound with at least 1 hour lifetime to remain clearly below safety limits for Cb concentrations.

[0141] In general, methane slip on a modern engine may be around 2.3-3.0 g / kWh at 54-80% loads, but increasing to 10 g / kWh at 25% load and 21 g / kWh at 12% load. These values may apply for a 4-stroke low-pressure dual fuel engine on-board a newly built cruise ship. The respective weighted emission factor, representing the actual engine operation, may result in methane slip of 2.8 g / kWh or 1.7% of the fuel use. To put this in perspective, NOx emissions from an LNG fueled ship may be between 0.7 and 2.6% of fuel use.

[0142] In this modelling case, a 1.7% (17 gram per kg fuel) methane slip was applied, which increased CH4 concentrations from a background of 1.78 ppm to an elevated concentration of 1.92 ppm at 600 meter distance (3.6 minutes after emission). Using an estimated 0.2 gram methane removed per gram Ch or NaOCl emitted, the methane emission of 17 gram per kg fuel would be removed with 85 gram Ch or NaOCl per kg fuel (44 g / s). Modelling showed that indeed 85 gram of chlorine-comprising compound emission was able to reduce CH4 concentrations to below the background air concentration, within 20 km from the ship. The removal by NaOCl was delayed compared to Cb (as expected), and had a similar removal performance. The methane removal was also shown to continue after the Ch / NaOCl had been consumed, which was hypothesized to be because the Cb / NaOCl emissions may haveimproved (NOx) conditions in favor of methane removal, giving further methane removal beyond the lifetime of the chlorine-comprising compound. Leveraging the ship NOx emissions may improve efficiency by 4x.

[0143] Note that 85 gram of CI2 per kg fuel may be 8.5% of fuel mass, but this may not be the amount of fuel used to generate electricity. Using 4600 kWh per ton fuel, the extra fuel consumption to generate 85 gram CI2 per kg fuel would be 6% (and 2% if NOx emissions are leveraged).

[0144] It is noted that the pollution removal system may only operate during daylight, leaving some methane emissions not removed. However, since the methane removal during the daytime may reach efficiencies exceeding the methane emission during said daytime, the nighttime methane emissions may be removed (effectively using up the excess “removal space”) during daylight. If daylight is 8 hours per day, this means that during the day the methane removal may need to be 3 times the methane emission, to compensate for 24 hours of operation. In the current example, an emission of 170 g chlorine-comprising compound per kg fuel during 8 daylight hours would compensate for 24 hours of operation.

[0145] Modelling case 2 - methane removal from using a wind turbine The method of the invention may further be applied to remove general pollution from the atmosphere, preferably removing methane from the general atmosphere.

[0146] When removing methane from the general atmosphere, there is no synergy with NOx pollution emitted by the exhaust, due to which the NOx background concentrations cannot be controlled. The implication of this may be that a local relatively high intensity of chlorinecomprising compound may be necessary to achieve similarly high efficiency in methane removal as compared to the case using the exhaust of a ship.

[0147] An advantage of the current invention may be that the removal efficiency for methane may be optimized through high-intensity local CI2 concentrations, using a chlorinecomprising compound as described herein. The advantage of a chlorine-comprising compound having a relatively long lifetime (up to 8 hours) may be that a higher methane removal capacity may be achieved with one emission source, while a the advantage of a chlorine-comprising compound having a relatively shorter lifetime (3 hours, 1 hours, or direct Ch) may be that there may be more control over the tropospheric space influenced by the method, and there may be lower loss due to deposition, or due to night-time dynamics.

[0148] Portable systems may be used to inject the chlorine-comprising compound in the atmosphere (especially in the tropospheric space). For example, in this case the methane removal system may be integrated with an off-shore wind turbine. The embodiment thereforemay comprise a wind-turbine that generates electricity, and the electricity may be used as input into a production device for the chlorine-comprising compound, while the chlorine-comprising compound may be released near the top of the tower of the wind turbine. The synergy in this approach may be that: (i) wind turbines generally generate power at low cost, (ii) the height of the tower may be leveraged for the release of the chlorine-comprising compound (a typical altitude for an off-shore wind turbine may be 80-130 meters), which may help to prevent high Cb concentrations near the surface, and (iii) release at high altitude may be especially important when using a chlorine-comprising compound that releases Ch indirectly, such as NaOCl, because it may be an advantage to release NaOCl aerosols at high enough altitude to prevent them from depositing into the ocean before they are converted into Ch.

[0149] These capacities of a wind turbine would allow substantial removal of Cth, in a very cost-effective way. For example, a large offshore 10 MW wind turbine may have a capacity factor of on average 45%, generating 10MW x 0.45 x 24hours / day x 365days / year=39 million kWh / year. Such energy levels may be used to produce about 11.000 ton Ch or NaOCl per year, with which about 2200 ton of methane may be removed. The emission in this example may be 1000 g / s chlorine-comprising compound, which may result in about 4 ppb of Ch near the wind turbine (in case the chlorine-comprising compound comprises Ch), and 0.4 ppb of Ch (in case the chlorine-comprising compound comprises NaOCl).

[0150] Laboratory demonstration of NaOCl aerosols

[0151] NaOCl may be aerosolized, and react with HC1 that may be taken up from the atmosphere. The reaction that follows may be given by:

[0152] NaOCl+2 HO— Ch + NaCl + H2O ( 1 )

[0153] A 5% NaOCl solution was aerosolized by adding 50 pg / m3to a smog chamber that was pre-loaded with 2 ppb HC1 background concentration. The average particle size was determined at 100 nm. The produced NaOCl aerosols had a surface area of about 60 pm2per pm3aerosol (6 x 107m2aerosol surface per m3aerosol). Using an NaOCl density of 1110 kg / m3, the mass of 50 pg in a m3of air has a volume of 4.5 x 10'nm3, and this would have a surface area of 2.7 10’3m2aerosol surface in a m3of air.

[0154] The net gas flux of gas X from the gas phase to the condensed phase Let (mol per m2per s) may be expressed as:

[0155]

[0156] wherein co may be the mean thermal velocity (here 300 m / s was applied), and yeff may be the effective uptake coefficient, giving the fraction of gas molecules that are taken up when the molecules impact on the aerosol surface (here yeff = 0.06 was used), and [Xg] maybe the average gas concentration far away from the aerosol surface (here 2 ppb HC1 = 4.92 x 1016molecules / m3was used). Applying the described values results in Let = 22.15 x 1016molecules / m2 / s. Multiplying this with the surface area of 2.7 x 10'3m2leads to a total HC1 uptake of 5 ppt per second (20 ppb per hour). In this example the lifetime of the NaOCl may be around 5 minutes, because to fully consume 8 ppb of NaOCl, the same amount of HC1 would need to be taken up (accounting for the effect of CO2 uptake), while 100 ppb may be taken up per hour.

[0157] In this laboratory demonstration the HC1 background concentration was much greater than the concentration of NaOCl that was introduced. Conversely, in a practical application background acids may become depleted if the NaOCl concentration exceeds the acid concentration. Such a scenario was modelled using a 0D box model of the ocean atmosphere with integrated plume dispersion, with added reactions to model individual steps including: (i) CO2 uptake converting NaOCl into HOC1 and NaHCOi, (ii) HCI / HNO3 uptake or HOC1 photolysis leading to the release of CI2 gas, and (iii) once HOC1 would be depleted HCI / HNO3 uptake releasing the CO2 that was taken up at the start. The model output confirmed that CO2 and HNO3 uptake may lead to a temporary increase in HC1 concentrations close to the ship that may accelerate the conversion of NaOCl to Ch. In the modelled example, HC1 concentrations in the ambient atmosphere were low, due to which HC1 was depleted close to the ship (due to reaction with NaOCl or HOC1). That may be why the uptake of CO2 helped accelerate the conversion of NaOCl to Ch by providing a temporary boost in HC1. Further, the modelling demonstrated the advantage of NaOCl dispersion over HOC1 dispersion, because NaOCl dispersion may only lead to a temporary increase in HC1, while HOC1 dispersion may lead to a longer-term increase in HC1 concentrations. Hence, modelling of a scenario where background acids are depleted showed that this depletion effect delays the initial conversion of NaOCl to CI2. As such, the depletion effect may lead to lower CI2 concentrations close to the ship (before the plume disperses and mixes in more acids from ambient air, or before NOx emissions convert to HNO3 acid). Hence, such scenario’s may be advantageous in view of safety for ship crews. Furthermore, the effect of photolysis was included in the modelling, due to which it was found that conversion of NaOCl to Ch may be accelerated (leading to shorter NaOCl lifetime).

[0158] In the above modelling example, the chlorine comprising compound NaOCl aerosols were added to a vessel plume. Due to high CO2 concentrations, the NaOCl aerosols were rapidly acidified by capturing CO2. This reduced the pH and converted NaOCl into HOC1. Additional uptake of acids was needed to finally convert the HOC1 to Ch. For example, uptakeof acids such as HC1 and HNO3 may lead to Ch production. The CI2 may subsequently be photolyzed by UV (e.g. from sunlight) to form chlorine atoms that may oxidize methane in the ship plume. The modelling showed that CO2 uptake may provide advantages (for example in scenario’s where conversion is limited by acid availability) by accelerating the conversion of NaOCl to Ch. At the same time, additional HC1 may be released that may increase the local acidity, further accelerating the conversion of NaOCl to CI2. Finally, the additional HC1 may be consumed in a reaction with captured CO2 to release the CO2 again. If the additional HC1 instead is neutralized (e.g. by reaction with silicate mineral dust or rocks), the CO2 remains captured, leading to additional climate benefits through CO2 reduction in the atmosphere.

[0159] In the abovementioned modelling example an NaOCl emission of 44 gram per second was used (which would be sufficient to compensate for 9 gram per second methane leakage in the specific example of a vessel with an LNG-based engine emitting 17 gram methane per kg fuel and consuming 1.875 ton fuel per hour). In such an example, the model output showed peak CI2 concentrations below 0.02 ppm at 2-4 km distance, and with CI2 concentrations below 0.002 ppm within the first 600 meters from the vessel. The model output therewith demonstrated that indeed NaOCl emission may keep CI2 concentrations below 0.05 ppm within 50 meters of the vessel.

[0160] The term “plurality” refers to two or more. Furthermore, the terms “a plurality of’ and “a number of’ may be used interchangeably. The terms “substantially” or “essentially” herein, and similar terms, will be understood by the person skilled in the art. The terms “substantially” or “essentially” may also include embodiments with “entirely”, “completely”, “all”, etc. Hence, in embodiments the adjective substantially or essentially may also be removed. Where applicable, the term “substantially” or the term “essentially” may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%. Moreover, the terms ’’about” and “approximately” may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%. For numerical values it is to be understood that the terms “substantially”, “essentially”, “about”, and “approximately” may also relate to the range of 90% - 110%, such as 95%- 105%, especially 99%- 101 % of the values(s) it refers to. The term “comprise” also includes embodiments wherein the term “comprises” means “consists of’. The term “and / or” especially relates to one or more of the items mentioned before and after “and / or”. For instance, a phrase “item 1 and / or item 2” and similar phrases may relate to one or more of item 1 and item 2. The term "comprising" may in an embodiment refer to "consisting of but may in another embodiment also refer to "containing at least the defined species andoptionally one or more other species". Use of the verb "to comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, “include”, “including”, “contain”, “containing” and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein. The term “further embodiment” and similar terms may refer to an embodiment comprising the features of the previously discussed embodiment, but may also refer to an alternative embodiment.

[0161] The devices, apparatus, or systems may herein amongst others be described during operation. As will be clear to the person skilled in the art, the invention is not limited to methods of operation, or devices, apparatus, or systems in operation. It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim.

[0162] The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In a device claim, or an apparatus claim, or a system claim, enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. The invention may also provide a control system that may control the device, apparatus, or system, or that may execute the herein described method or process. Yet further, the invention also provides a computer program product, when running on a computer which is functionally coupled to or comprised by the device, apparatus, or system, controls one or more controllable elements of such device, apparatus, or system.

[0163] The invention further applies to a device, apparatus, or system comprising one or more of the characterizing features described in the description and / or shown in the attached drawings. The invention further pertains to a method or process comprising one or more of thecharacterizing features described in the description and / or shown in the attached drawings. Moreover, if a method or an embodiment of the method is described being executed in a device, apparatus, or system, it will be understood that the device, apparatus, or system is suitable for or configured for (executing) the method or the embodiment of the method, respectively.

[0164] The various aspects discussed in this patent can be combined in order to provide additional advantages. Further, the person skilled in the art will understand that embodiments can be combined, and that also more than two embodiments can be combined. Furthermore, some of the features can form the basis for one or more divisional applications.

Claims

1. CLAIMS:

1. A method for removing a pollutant (5) from a tropospheric space (500), wherein the method comprises:injecting a chlorine-comprising compound (1) into a gaseous flow (50), wherein the gaseous flow (50) is provided in the tropospheric space (500) during daytime; wherein one or more of (a) the gaseous flow (50) and (b) the tropospheric space (500) comprise the pollutant (5); andallowing the pollutant (5) to react, in the tropospheric space (500), with chlorine radicals (2) produced from the chlorine-comprising compound (1).

2. The method according to claim 1, wherein the chlorine-comprising compound (1) comprises a precursor for chlorine gas (3); and wherein the pollutant (5) comprises one or more of the group comprising: methane, a volatile organic compound, ozone, and nitrogen oxides.

3. The method according to any one of the preceding claims, wherein the chlorinecomprising compound (1) comprises sodium hypochlorite; wherein the pollutant (5) comprises methane.

4. The method according to any one of the preceding claims, wherein nighttime emissions of the chlorine-comprising compound (1) into the gaseous flow (50) are at least 10 times less than daytime emissions of the chlorine-comprising compound (1) into the gaseous flow (50).

5. The method according to any one of the preceding claims, wherein the tropospheric space (500) is in a maritime region, defined as a space or volume defined at a height (hi) as measured from sea-level (a) above the sea surface, (b) above the ocean surface, or (c) above an area of land within a shortest distance (di ) of 3 km from an ocean or a sea; and wherein the height (hi) is selected from the range of 0.5-4 km.

6. The method according to any one of the preceding claims, wherein the gaseous flow (50) comprises one or more of (i) an acid and (ii) an acid precursor; especially in aconcentration of at least 50 ppt, wherein the one or more of an acid and an acid precursor is selected from the group comprising: HC1, HNO3, H2SO4, SO2, NO2, and HCOOH.

7. The method according to any one of the preceding claims, wherein the gaseous flow (50) is an exhaust stream (90) of a target object (400), wherein one of the following applies:the exhaust stream (90) comprises the pollutant (5); orthe exhaust stream (90) does not comprise the pollutant (5), wherein the pollutant (5) is atmospherically present in the tropospheric space (500).

8. The method according to claim 7, wherein the target object (400) comprises:a vessel (410), wherein the vessel (410) is selected from the group comprising: a ship, a barge, a yacht, an oiler, a buoy, and a tanker; wherein the vessel (410) comprises an exhaust device (250) configured to provide the exhaust stream (90); ora structure (420), wherein the structure (420) is selected from the group comprising: an oil platform, a wind turbine (425), and a flare stack; wherein the structure (420) is or comprises a flow generating device (200).

9. The method according to claim 8, wherein the vessel (410) is fueled by a methane-comprising fuel; wherein the method further comprises maintaining a maximum chlorine gas (Ch) concentration within a radius of 50 m of the vessel (410) of at most 0.05 ppm.

10. The method according to any one of the preceding claims, wherein the method further comprises producing the chlorine-comprising compound (1) from a salt water comprising starting material using electrolysis techniques.

11. The method according to any one of the preceding claims, wherein the chlorinecomprising compound (1), in the step of injection the chlorine-comprising compound (1) into the gaseous flow (50), is provided as aerosol particles having particle sizes selected from the range of 0.01-10 pm.

12. The method according to any one of the preceding claims, the method further comprises:deriving an environmental parameter from the tropospheric space (500) using one or more sensors (310), wherein the sensors are configured to generate a sensor signal corresponding to the environmental parameter, wherein the environmental parameter is selected from one or more of: sunlight, chlorine gas concentration, humidity, nitrogen oxide concentration, wind speed, and weather conditions; andcontrolling an injection rate for injecting the chlorine-comprising compound (1) into the gaseous flow (50) in dependence of the sensor signal.

13. A pollution removal arrangement ( 1000) configured for removing a pollutant (5) from a tropospheric space (500), the pollution removal arrangement (1000) comprising an injection device (100), a flow generating device (200), and a control system (300), wherein:the flow generating device (200) is configured to generate a gaseous flow (50) into the tropospheric space (500);the injection device (100) is configured to inject a chlorine-comprising compound (1) into the gaseous flow (50);the control system (300) is configured to control an injection rate for injecting the chlorine-comprising compound (1) into the gaseous flow (50).

14. The pollution removal arrangement (1000) according to claim 13, wherein the chlorine-comprising compound (1) comprises sodium hypochlorite; the pollution removal arrangement (1000) further comprising a chlorine-comprising compound production device (600), wherein the chlorine-comprising compound production device (600) is configured to convert a salt water starting material into the chlorine-comprising compound (1) using electrolysis techniques.

15. The pollution removal arrangement ( 1000) according to any one of the preceding claims 13-14, further comprising one or more sensors (310) as defined in claim 12, wherein the control system (300) is configured to control an injection rate for injecting the chlorinecomprising compound (1) into the gaseous flow (50) in dependence of the sensor signal.

16. The pollution removal arrangement (1000) according to any one of the preceding claims 13-15, further comprising a sensor unit (900) configured to quantify the amount of atmospheric methane removal by the pollution removal arrangement (1000), wherein the sensor unit (900) comprises an outlet (909), a sensor reactor (950), a first pollutant sensor (910) and asecond pollutant sensor (920); wherein the outlet (909) is configured downstream of the injection device (100); wherein the sensor reactor (950) is configured to receive a sample of the gaseous flow (50) comprising the chlorine-comprising compound (1) via the outlet (909); wherein the sensor reactor (950) comprises one or more radiation devices configured to provide first radiation to the sample of the gaseous flow (50); wherein the first radiation is selected such that the first radiation activates the chlorine-comprising compound (1) to generate chlorine radicals (2); wherein the first pollutant sensor (910) is configured upstream of the sensor reactor (950); wherein the second pollutant sensor (920) is configured downstream of the sensor reactor (950); wherein the first pollutant sensor (910) and the second pollutant sensor (920) are configured to measure a pollutant concentration in the sample of the gaseous flow (50).

17. A target object (400) comprising the pollution removal arrangement (1000) according to any one of the preceding claims 13-16, wherein the target object (400) comprises:a vessel (410), wherein the vessel (410) is selected from the group comprising: a ship, a barge, a yacht, an oiler, a buoy, and a tanker; wherein the target object (400) is configured to generate the gaseous flow (50), and wherein the target object (400) comprises an exhaust device (250) configured to generate an exhaust stream (90), wherein the gaseous flow (50) comprises the exhaust stream (90); ora structure (420), wherein the structure (420) is selected from the group comprising: an oil platform, a wind turbine (425), and a flare stack.

18. Use of the pollution removal arrangement (1000) according to any one of the preceding claims 13-16 for removing methane slip of a target object (400) according to claim 17 in a tropospheric space (500).

19. A method for functionally coupling a pollution removal arrangement (1000), as defined in any one of claims 13-16, to a target object (400), as defined in claim 17, wherein the method comprises:functionally coupling an injection device (100) and a control system (300), to the target object (400), and when the target object (400) does not comprise a flow generating device (200), also functionally coupling a flow generating device (200) to the target object (400).

20. The method according to claim 19, wherein the target object (400) comprises a vessel (410), wherein the vessel (410) is selected from the group comprising: a ship, a barge, a yacht, an oiler, a buoy, and a tanker; wherein the target object (400) is configured to generate the gaseous flow (50), and wherein the target object (400) comprises an exhaust device (250) configured to generate an exhaust stream (90), wherein the gaseous flow (50) comprises the exhaust stream (90);21. The method according to claim 19, wherein the target object (400) comprises a structure (420), wherein the structure (420) is selected from the group comprising: an oil platform, a wind turbine (425), and a flare stack; and wherein the structure (420) is or comprises a flow generating device (200).

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