Device for measuring atmospheric ozone concentration and atmospheric nitrogen dioxide concentration

Abstract

Device for measuring atmospheric ozone and nitrogen dioxide concentrations. Device (1) for measuring atmospheric ozone and nitrogen dioxide concentrations, the device comprising a data acquisition module (5) having first (10) and second (15) identical metal oxide resistive sensors configured to measure total atmospheric nitrogen oxide and ozone concentrations, the first sensor (10) being covered with an ozone-tight, nitrogen dioxide-permeable filter (30). Figure for the abstract: Fig. 1

Description

Title of the invention: Device for measuring atmospheric ozone concentration and atmospheric nitrogen dioxide concentration

[0001] The present invention relates to the field of measurement and detection of atmospheric pollutants, and more specifically of ozone and nitrogen oxide.

[0002] In the lower layers of the atmosphere, ozone is produced by the action of solar (UV) radiation on other pollutants, particularly industrial or automotive pollutants, such as hydrocarbons or nitrogen oxides. Ozone is an allotropic form of oxygen that has a long lifespan and can be transported over long distances. Ozone has a significant impact on health, causing inflammation of the mucous membranes of the eyes, bronchi, and bronchioles, which can lead to asthma or even respiratory mortality when present in excessively high concentrations. Furthermore, an overconcentration of ozone also causes necrosis in plants and leads to the decline of ecosystems.

[0003] Nitrogen dioxide results primarily from the combustion of hydrocarbons, particularly from road traffic, industry, and thermal power plants. It can cause bronchial inflammation and lead to respiratory complications. From an environmental perspective, an overconcentration of nitrogen dioxide induces acidification and eutrophication of wetlands, particularly freshwater.

[0004] In order to limit the harmful effects of these pollutants, European Directive 2008 / 50 / EC of May 2008 regulates the maximum permissible atmospheric concentrations.

[0005] In particular, for ozone, it sets an average exposure limit value of 120 pg / m³ over an 8-hour period, which must not be exceeded for more than 25 days per year, an alert threshold for an average atmospheric concentration measured over an 8-hour period of 120 pg / m³, and a critical hourly average level of 180 pg / m³. For nitrogen oxide, the Directive sets an annual average exposure limit value of 40 pg / m³ and a maximum annual average of 200 pg / m³ for 18 hours per year, as well as an alert threshold of 400 pg / m³ for an hourly average over a period of 3 consecutive hours.

[0006] Measuring such low atmospheric concentrations of ozone and nitrogen requires specific devices that are sufficiently sensitive and allow for reproducible measurements. Metal oxide resistive sensors are known, such as the The MICS 2714 reference sensor, marketed by SGX Sensortech®, features a sensitive layer whose electrical conductivity changes upon contact with ozone and nitrogen dioxide. Its advantage lies in measuring atmospheric concentrations across a wide range, from a few ppb (parts per billion) to several ppm (parts per million), and it offers a fast response time. Furthermore, it is compact, inexpensive, and has a lifespan of several years. Unfortunately, it is not very selective; that is, it measures the total atmospheric concentration of both ozone and nitrogen dioxide without being able to distinguish between the two pollutants during the measurement.

[0007] It is also known to measure total atmospheric concentrations of ozone and nitrogen dioxide using electrochemical cells, by measuring the electric current generated by the interaction of these gases with a solid electrolyte. Unlike resistive sensors, the electrolysis of ozone and nitrogen dioxide is a selective technique. However, it can only detect atmospheric concentrations of nitrogen dioxide and / or ozone within a limited range, from 20 ppb to 300 ppb. Furthermore, its response time is slow, and an electrolysis cell generally has a limited lifespan of less than two years.

[0008] To measure such a low atmospheric concentration of ozone efficiently and accurately, another known method is UV photometry implemented according to standard EN 14625:2013. UV photometry is based on the absorption of radiation in the spectral range within the ultraviolet. In this wavelength range, ozone exhibits a specific absorption band distinct from other gases.

[0009] To measure a low atmospheric concentration of nitrogen dioxide, it is still known to implement chemiluminescence following the requirements of standard EN14211:2012. Chemiluminescence consists of detecting a light emission resulting from a chemical reaction between nitrogen dioxide and luminol.

[0010] However, UV photometry and chemiluminescence require specific, bulky (generally longer than 50 cm), heavy (often weighing over 10 kg), and expensive devices. Furthermore, these devices require the addition of external pumps and a power supply from the grid. Therefore, they can only be implemented in a limited number of fixed air quality monitoring stations.

[0011] There is therefore a need for a device for measuring atmospheric ozone concentration and atmospheric nitrogen oxide concentration in the air which is selective, robust and simple to implement.

[0012] Furthermore, to improve the spatial and temporal resolution of air quality forecasting models, it is necessary to have a greater number of local measurements of atmospheric concentrations of ozone and nitrogen dioxide than those available to date.

[0013] There is therefore also a need for a device for measuring atmospheric ozone concentration and atmospheric nitrogen oxide concentration that is easily transportable and can be easily deployed in many locations.

[0014] The invention aims to meet at least one of these needs, and it achieves this by means of a device for measuring atmospheric ozone concentration and atmospheric nitrogen oxide concentration, the device comprising an acquisition module having first and second identical sensors, of the resistive metal oxide type, and configured to measure a total atmospheric concentration of nitrogen oxide and ozone, the first sensor being covered with a filter that is impermeable to ozone and permeable to nitrogen dioxide.

[0015] The invention simply allows, by selectively filtering the ozone reaching the first sensor, for overcoming the inherent lack of selectivity in metal oxide-type sensors, while retaining the advantages of these sensors previously mentioned. The device also allows for the measurement of atmospheric nitrogen oxide concentration and atmospheric ozone concentration within ranges covering those specified in European Directive 2008 / 50 / EC of May 2008.

[0016] Preferably, the device includes a processing module for determining the atmospheric concentration of nitrogen oxide by subtracting the atmospheric concentration of nitrogen oxide measured by the first sensor from the total atmospheric concentration of nitrogen oxide and ozone measured by the second sensor. The measurement of each of the atmospheric concentrations of ozone and nitrogen oxide can thus be obtained by a simple subtraction operation.

[0017] Preferably, the first and second sensors are spaced less than 100 cm apart, preferably less than 20 cm, and even better less than 5 cm. A close distance between the sensors ensures that the measured atmospheric concentrations of ozone and nitrogen oxide are representative of the same sample of the atmosphere around the device.

[0018] By "ozone-tight" filter, it is considered that a quantity of ozone can pass through the filter, but in a concentration lower than the detection limit of each of the first and second sensors.

[0019] The filter comprises an ozone-trapping material which can be selected from potassium iodide, polyphenylene sulfide and mixtures thereof.

[0020] Preferably, the ozone-trapping material is potassium iodide.

[0021] Preferably, the filter comprises a porous fibrous support whose fibers are re covered partially, preferably entirely, by the trapping material ozone.

[0022] The fibrous support can be selected from paper, glass fiber veil, woven fabric, and non-woven fabric. Preferably, the fibrous support is paper, preferably acid-free.

[0023] The fibrous support may have a basis weight of between 10 and 30 g / m2, in particular between 15 and 20 g / m2.

[0024] The fibrous support can extend over an area less than or equal to 1 cm2.

[0025] The first sensor may be partially or completely covered by the filter so as to prevent ozone from accessing the sensitive layer of said sensor. The wire may completely cover the sensitive layer of the first sensor.

[0026] The filter can be separated from the first sensor by a distance less than or equal to 5 mm, preferably less than or equal to 1 mm.

[0027] The second sensor is preferably entirely not superimposed on the filter.

[0028] Each sensor may have a length less than or equal to 1 cm.

[0029] Each sensor can be of the resistive type with metal oxide among SnO2, Ta2O5, WO3, In2O3, ZnO and their mixtures.

[0030] Preferably, the mass of the measuring device is less than 50 g and / or the volume of the measuring device is less than 1 cm3. The measuring device can thus be easily moved.

[0031] Furthermore, the device may include a housing, with the acquisition module and the processing module housed within the housing. The housing may have a volume of less than 1000 cm³.

[0032] In one variant, the processing module can be at a distance greater than 10 cm, or even greater than 1 m, from the acquisition module.

[0033] The processing module can be connected to the acquisition module via a wired connection, particularly when both the acquisition and processing modules are housed within the chassis. Alternatively, the processing module can be connected to the acquisition module wirelessly, for example via WiFi, Bluetooth®, or Zigbee.

[0034] The invention further relates to an object comprising the device according to the invention, the object being chosen from among a measurement station for the home, an air monitoring measurement station, a station for evaluating individual exposure to ozone and / or nitrogen dioxide, and an element of a motor vehicle.

[0035] The invention further relates to a method for manufacturing a device according to the invention, the method comprising: (i) the preparation of a composition by mixing the ozone-trapping material with a solvent, in particular an aqueous solvent, ii) impregnation of the support with the composition, iii) and drying, in particular by heating, of the composition in order to evaporate the solvent.

[0036] Step i) may include dissolving the ozone-trapping material in the solvent.

[0037] The invention also relates to a method for measuring atmospheric ozone concentration and atmospheric nitrogen oxide concentration, the method comprising a) the supply of a device according to the invention, b) the joint measurement of atmospheric ozone concentration using the first sensor and total atmospheric ozone and nitrogen dioxide concentration using the second sensor, and c) the determination of the atmospheric concentration by subtracting the measured atmospheric concentration of nitrogen oxide from the total atmospheric concentration of nitrogen oxide and ozone measured in step b).

[0038] The invention will be better understood upon reading the detailed description and the accompanying drawing which follows, in which

[0039] [Fig-1] is a schematic cross-sectional view of an example device according to the invention,

[0040] [Fig.2] is a photograph of an example of a device according to the invention,

[0041] [Fig.3] are graphs representing the measurement of atmospheric ozone concentration measured by each of the first and second sensors of the device illustrated in [Fig.2] and subjected to an ozone-regulated atmosphere, and

[0042] [Fig.4] are graphs representing the measurement of atmospheric nitrogen dioxide concentration measured by each of the first and second sensors of the device illustrated in [Fig.2] and subjected to a nitrogen dioxide regulated atmosphere.

[0043] An example of the embodiment of a device 1 according to the invention has been schematically illustrated in [Fig.1].

[0044] The device 1 includes an acquisition module 5 of the first 10 and second 15 identical sensors, which are carried by a support 20. They are separated from each other, for example by a distance d of less than 1 cm.

[0045] The sensors are of the resistive metal oxide type. They each comprise a sensitive layer 25 whose electrical resistivity varies upon contact with nitrogen dioxide and / or ozone.

[0046] The sensitive layer of the first sensor is covered by a filter 30, for example made of acid-free paper whose fibers are coated with potassium iodide. In this way, the ozone is trapped by the potassium iodide and cannot reach the sensitive layer. The first sensor 10 thus measures only the atmospheric concentration of nitrogen oxide.

[0047] On the contrary, the surface of the second sensor 15 is in direct contact with the atmosphere and can thus measure the total atmospheric concentration of ozone and nitrogen oxide.

[0048] By subtracting the atmospheric concentration of nitrogen oxide measured by the first from the total atmospheric concentration of nitrogen oxide and ozone, the atmospheric concentration of ozone can thus be easily determined.

[0049] Preferably, the device includes a processing module 35 connected to the acquisition module and configured to perform this mathematical subtraction operation.

[0050] Fig. 2 is a photograph of a prototype device according to the invention, which represents a first sensor 15 covered by a filter 30.

[0051] This first sensor, like the second sensor, is of reference MICS 2714 marketed by SGX Sensortech®. It is coated with a non-acidic paper filter coated with potassium iodide which has been manufactured in the following way.

[0052] 75 g of potassium iodide were dissolved in 100 ml of distilled water using using a magnetic stirrer to form a filter composition. After one hour of mixing, the proper dissolution of the potassium iodide is confirmed by visual observation by checking the transparency, homogeneity and absence of precipitates in the filter composition.

[0053] A sample of acid-free reference paper AFT500750, marketed by Lightning Packaging®, was then immersed in the solution and subsequently dried on a hot plate for 12 hours at a temperature of 50 °C to evaporate the water from the filter composition. As seen in the inset in [Fig. 2], the fibers of the acid-free paper are coated by a potassium iodide deposit.

[0054] The performance of the device is illustrated by the curves in Figures 3 and 4.

[0055] The curves in [Fig. 3] represent the evolution over time of the concentration atmospheric ozone measured by the first and second sensors. For the measurement illustrated in [Fig.3], the device was introduced into an enclosure whose atmosphere, of controlled composition, is free of nitrogen dioxide and whose atmospheric ozone concentration has been regulated.

[0056] The second sensor, not covered by the filter, measures the change in ozone concentration as a function of the regulation of atmospheric ozone concentration, as observed on the dashed curve. The first sensor, covered by the filter, measures no atmospheric ozone concentration when ozone is injected into the enclosure, thus demonstrating the ozone-tightness of the filter.

[0057] The curves in [Fig. 4] represent the evolution over time of the atmospheric concentration of nitrogen dioxide measured by the first and second sensors. For the measurement illustrated in [Fig. 4], the device was introduced into an enclosure whose atmosphere, of controlled composition, is free of ozone and whose atmospheric concentration of nitrogen dioxide has been regulated.

[0058] The first and second sensors each measure an atmospheric concentration of nitrogen dioxide, which is lower for the first sensor, highlighting the ozone permeability of the filter.

[0059] As has become apparent throughout the description, the invention allows for the simple and selective measurement of ozone and nitrogen oxide concentrations using sensitive, robust, lightweight, and inexpensive sensors. Obviously, the invention is not limited to the embodiments shown in the illustrative examples in the description.

Claims

Demands

1. Device (1) for measuring atmospheric ozone concentration and atmospheric nitrogen dioxide concentration, the device comprising an acquisition module (5) having first (10) and second (15) identical sensors, of the resistive metal oxide type, and configured to measure a total atmospheric concentration of nitrogen oxide and ozone, the first sensor (10) being covered with a filter (30) that is impermeable to ozone and permeable to nitrogen dioxide, the filter comprising an ozone-trapping material selected from potassium iodide, polyphenylene sulfide and mixtures thereof and a porous fibrous support the fibers of which are at least partially covered by the ozone-trapping material.

2. Device according to claim 1, comprising a processing module (35) for determining the atmospheric concentration of nitrogen oxide, by subtracting the atmospheric concentration of nitrogen oxide measured by the first sensor (10) from the total atmospheric concentration of nitrogen oxide and ozone measured by the second sensor (15).

3. A device according to any one of claims 1 and 2, the first and second sensors being spaced apart by a distance (d) of less than 100 cm, preferably less than 20 cm, better less than 5

4. cm. Device according to any one of the preceding claims, the mass of the measuring device being less than 50 g and / or the volume of the measuring device being less than 1 cm3.

5. Device according to any one of the preceding claims, the ozone-trapping material being potassium iodide.

6. Device according to any one of the preceding claims, the fibers being entirely covered by the ozone-trapping material.

7. Device according to any one of the claims, the fibrous support being paper, preferably acid-free.

8. Device according to any one of the preceding claims, the metal oxide being selected from SnO2, Ta2O5, WO3, In2O3, ZnO and mixtures thereof.

9. A method for manufacturing a device according to any one of the preceding claims, the method comprising: i) preparing a composition by mixing the trapping material ozone with a solvent, in particular aqueous. ii) impregnation of the support with the composition, iii) and drying, in particular by heating, of the composition in order to evaporate the solvent.

10. Method for measuring atmospheric ozone concentration and atmospheric nitrogen oxide concentration, the method comprising a) providing a device according to any one of claims 1 to 9, b) jointly measuring atmospheric ozone concentration by means of the first sensor and total atmospheric ozone and nitrogen dioxide concentration by means of the second sensor, and c) determining the atmospheric concentration by subtracting the measured atmospheric nitrogen oxide concentration from the total atmospheric nitrogen oxide and ozone concentration measured in step b).

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