Multi-channel active nitrogen classification measurement system and method based on high-precision cavity

Abstract

The invention discloses a multi-channel active nitrogen classification measurement system and method based on a high-precision cavity, and relates to the technical field of trace detection, micro-element analysis, atmospheric environment monitoring and high-precision cavities. A gas inlet module inputs sampled gas into a humidity control module, a pyrolysis module and a high-precision cavity measurement module; the sampling gas is ambient atmosphere or ambient atmosphere after filtering reaction gas; the humidity control module inputs the humidified gas into the pyrolysis module; the pyrolysis module comprises a plurality of pyrolysis units with different pyrolysis temperatures and is used for inputting directly sampled gas and humidified gas; the pyrolysis unit is used for performing pyrolysis separation on nitric acid and nitrate ester in the ambient atmosphere to generate nitrogen dioxide gas; all the gases are subjected to temperature control by the water bath heating module and then enter the high-precision cavity measurement module, and the concentration of nitrogen dioxide gas in each gas is measured by the high-precision cavity measurement module, so that the concentrations of different types of active nitrogen in the ambient atmosphere are obtained. The high-sensitivity measuring system and the high-sensitivity measuring method can accurately measure the concentration of different active nitrogen gases.

Description

Technical Field

[0001] The present invention relates to the technical fields of trace detection, microelement analysis, atmospheric environment monitoring and high-precision cavity technology, and in particular to a multi-channel active nitrogen classification measurement system and method based on a high-precision cavity. Background Art

[0002] Nitrates and nitric acid are important components of total active nitrogen, which can regulate ozone formation by promoting or inhibiting the HO x cycle and ultimately affect the atmospheric chemical composition, playing a crucial role in regulating ozone formation. In addition to being an indicator of photochemical ozone production, nitrates and nitric acid also directly affect regional ozone production, strongly affect the global distribution of NO x and ozone, and are generally considered important precursors of secondary organic aerosols (SOA). Therefore, it is particularly important to accurately measure the concentrations of different types of active nitrogen gases such as nitrates and nitric acid in ambient air. Nitrates and nitric acid are generally indirectly measured by thermally dissociating them into NO2 respectively and then using technical means such as cavity ring-down spectroscopy. However, when the concentrations of background gases such as nitrogen oxides or ozone in ambient air are relatively high, the peroxy organic radicals in the pyrolysis products are prone to undergo non-linear reverse reactions with them, resulting in low and unstable pyrolysis efficiency. There are also problems such as uneven heating and easy recombination of pyrolysis products leading to measurement deviations in multi-channel pyrolysis measurement. At the same time, due to the high temperature of the pyrolyzed gas, when using cavity ring-down spectroscopy to detect it, serious turbulence is easily generated, causing jitter and error in the measurement results. Moreover, the cavity ring-down spectroscopy technology requires using a protective gas to purge the mirror for protection, and the gas cylinder needs to be frequently replaced manually, which is not conducive to field experiment measurement. Summary of the Invention

[0003] In order to overcome the defects in the above-mentioned prior art, the present invention provides a multi-channel active nitrogen classification measurement system and method based on a high-precision cavity, which can realize the classification measurement of the concentrations of different types of active nitrogen gases in ambient air.

[0004] To achieve the above object, the present invention adopts the following technical solutions, including:

[0005] A multi-channel active nitrogen classification measurement system based on a high-precision cavity, including: an intake module, a humidity control module, a pyrolysis module, a water bath heating module, a high-precision cavity measurement module, and a signal processing module;

[0006] The intake module is used to respectively input the sampling gas into the humidity control module and the pyrolysis module, and directly input the sampling gas into the high-precision cavity measurement module through a direct sampling tube; the sampling gas is ambient air or ambient air after filtering the reaction gas; the reaction gas refers to active nitrogen gas;

[0007] The humidity control module is connected to the intake module, and is used for humidifying the sampled gas and inputting the humidified gas into the pyrolysis module;

[0008] The pyrolysis module contains a number of pyrolysis units with different pyrolysis temperatures, and is used for inputting the gas directly sampled by the intake module and the gas humidified by the humidity control module; the pyrolysis unit is used for pyrolytically separating active nitrogen in the ambient atmosphere to generate nitrogen dioxide gas;

[0009] The pyrolysis module is connected to the high-precision cavity measurement module through a water bath heating module, and is used for controlling the temperature of the pyrolyzed gas and then inputting it into the high-precision cavity measurement module; the direct sampling tube is also connected to the high-precision cavity measurement module through the water bath heating module, and is used for controlling the temperature of the directly sampled gas and then inputting it into the high-precision cavity measurement module;

[0010] The high-precision cavity measurement module is used for measuring the concentration of nitrogen dioxide gas; the signal processing module is used for performing real-time calculation and processing on the optoelectronic signal output by the high-precision cavity measurement module to obtain the concentrations of different types of active nitrogen in the ambient atmosphere.

[0011] Preferably, a filter membrane for filtering particulate matter in the ambient atmosphere is provided at the sampling port of the intake module; the intake module includes two gas paths, and an activated carbon tube for filtering reactive gas in the ambient atmosphere is provided on the first gas path; the intake module inputs the sampled gas passing through the first gas path or the second gas path into the humidity control module, the pyrolysis module and the high-precision cavity measurement module respectively.

[0012] Preferably, the pyrolysis module adopts an oil bath heating method and includes at least three pyrolysis units; each pyrolysis unit includes high-temperature heat-conducting oil and a spiral spring tube, and the high-temperature heat-conducting oil is used for uniformly and stably heating the spiral spring tube so that the gas in the spiral spring tube is fully heated and dissociated; among them, the spiral spring tube of the first pyrolysis unit inputs the gas directly sampled by the intake module, and the spiral spring tubes of the second pyrolysis unit and the third pyrolysis unit both input the gas humidified by the humidity control module.

[0013] Preferably, the high-precision cavity measurement module includes at least two cavity units with the same structure; among them, the first cavity unit is connected to the pyrolysis unit and is used for inputting the pyrolyzed gas; the second cavity unit is connected to the intake module and is used for inputting the directly sampled gas;

[0014] In the high-precision cavity measurement module, a broadband light in the absorption band of nitrogen dioxide gas is emitted by a light source, and the broadband light is collimated, stray light filtered and split, and then input into the two cavity units respectively.

[0015] Preferably, the cavity unit includes: a cavity, two highly reflective mirrors for causing broadband light input into the cavity to be reflected multiple times in the cavity, a filter for filtering out redundant bands from the broadband light output from the cavity, a focusing lens for focusing the broadband light after filtering out the redundant bands, a photomultiplier tube for performing photoelectric conversion on the focused broadband light to obtain an electrical signal, a pressure gauge for monitoring the internal pressure of the cavity in real time, an air pump for pumping gas into the cavity, and an extraction flowmeter for controlling the pumping speed of the air pump.

[0016] Preferably, the system further includes a temperature control and circulation module for controlling the temperature of each pyrolysis unit and the water bath heating module.

[0017] The present invention also provides a multi-channel active nitrogen classification measurement method based on a high-precision cavity. Using the multi-channel active nitrogen classification measurement system based on a high-precision cavity described above, the measurement principle is as follows:

[0018] The pyrolysis unit includes three pyrolysis units with different pyrolysis temperatures. Among them, the first pyrolysis unit inputs directly sampled gas and is used to pyrolyze nitric acid, peroxy nitrate, and alkyl nitrate in ambient air into nitrogen dioxide gas; the second pyrolysis unit inputs humidified gas and is used to pyrolyze peroxy nitrate and alkyl nitrate in ambient air into nitrogen dioxide gas, and nitric acid is not pyrolyzed; the third pyrolysis unit inputs humidified gas and is used to pyrolyze peroxy nitrate in ambient air into nitrogen dioxide gas, and nitric acid and peroxy nitrate are not pyrolyzed;

[0019] The nitrogen dioxide gas concentrations in the gases output from the three pyrolysis units are measured by the high-precision cavity measurement module as C 11 、C 12 、C 13 ; the nitrogen dioxide gas concentration in ambient air is directly measured by the high-precision cavity measurement module as C2;

[0020] Denote the concentration of nitric acid in ambient air as C H 、the concentration of peroxy nitrate as C P 、and the concentration of alkyl nitrate as C A . According to C P =C 13 -C2, C A =C 12 -C p 、C H =C 11 -C A , calculate the concentrations of different types of active nitrogen in ambient air.

[0021] Preferably, the calculation method for each nitrogen dioxide gas concentration is as follows:

[0022]

[0023] Among them, c is the speed of light; L1 and L2 are the ratios of the cavity length of the corresponding cavity to the single-pass absorption optical path length of the gas in the cavity; τ 11 is the decay time when the high-precision cavity measurement module measures the gas output by the first pyrolysis unit; τ 12 is the decay time when the high-precision cavity measurement module measures the gas output by the second pyrolysis unit, τ 13 is the decay time when the high-precision cavity measurement module measures the gas output by the third pyrolysis unit; τ 10 is the background decay time when there is no gas to be measured in the pyrolysis unit; τ2 is the decay time when the high-precision cavity measurement module measures the ambient atmosphere, τ 20 is the background decay time when the high-precision cavity measurement module measures the ambient atmosphere after filtering the reaction gas.

[0024] Preferably, the pyrolysis temperatures of the first, second, and third pyrolysis units are 600°C, 360°C, and 180°C respectively.

[0025] The present invention also provides a computer program product, which includes a computer program / instructions. When the computer program / instructions are executed by a processor, the described multi-channel active nitrogen classification measurement method based on a high-precision cavity is implemented.

[0026] The advantages of the present invention are as follows: [[ID=:22]]

[0027] (1) The present invention provides a multi-channel active nitrogen classification measurement system and method based on a high-precision cavity, aiming to remove peroxy organic free radicals in the pyrolysis products of active nitrogen gases, heat them evenly and sufficiently, maintain a stable and efficient pyrolysis efficiency, quickly cool the pyrolyzed gas to a constant value, ensure the temperature consistency of all gases entering the cavity, enable the gas flow to enter the high-precision cavity evenly and smoothly, achieve the constant temperature control of the high-precision cavity, without the need for additional purge gas, and finally accurately measure the concentrations of different types of active nitrogen gases by using a highly sensitive measurement method.

[0028] (2) The system of the present invention controls the humidity of the sampled gas, effectively removes organic peroxy free radicals in the pyrolysis products, and avoids their reaction or recombination with components such as nitrogen oxides and ozone, so as to maintain a stable and efficient pyrolysis efficiency in the background of high-concentration nitrogen oxides and ozone.

[0029] (3) The system of the present invention uses a spiral spring tube filled with quartz sponge instead of a straight tube to increase the surface area-to-volume ratio, intensify the free radical collision, and effectively improve the pyrolysis efficiency.

[0030] (4) The system of the present invention heats the spiral spring tube by means of oil bath heating, so that the pipeline can be heated evenly and sufficiently, and the temperature gradient inside the tube is reduced.

[0031] (5) The system of the present invention heats all the gas entering the cavity by water bath to ensure the consistency and stability of the temperature of the gas entering the cavity, so that the air flow enters the cavity uniformly and stably, eliminating the influence of turbulence and reducing the fluctuation of the measurement result. At the same time, maintaining the consistency of the gas entering the cavity helps to reduce the error in subsequent subtraction calculation of the concentration.

[0032] (6) The air intake module of the system of the present invention uses a resistance wire for heating, which can effectively avoid the influence of water on the measurement of nitric acid.

[0033] (7) The high-precision cavity measurement module of the system of the present invention uses integral resistance wire heating to eliminate the influence of water vapor on the high-reflection mirror, so that additional purge gas is not required.

[0034] (8) The system of the present invention can achieve the classification measurement of main active nitrogen gases such as nitric acid, organic nitrate and nitrogen dioxide. Description of the Drawings

[0035] Figure 1 It is a schematic structural diagram of a multi-channel active nitrogen classification measurement system based on a high-precision cavity of the present invention.

[0036] Figure 2 It is a schematic structural diagram of the high-precision cavity measurement module of the embodiment of the present invention.

[0037] Description of the Reference Numerals:

[0038] 1 - Filter membrane, 2 - Three - way solenoid valve, 3 - Activated carbon tube, 4 - Intake module, 5 - First three - way joint, 6 - Second three - way joint, 7 - Direct sampling tube, 8 - First four - way solenoid valve, 9 - First sampling tube, 10 - Second sampling tube, 11 - Third sampling tube, 12 - Humidity control module, 13 - First helical spring tube, 14 - First high - temperature heat - conducting oil, 15 - Second helical spring tube, 16 - Second high - temperature heat - conducting oil, 17 - Third helical spring tube, 18 - Third high - temperature heat - conducting oil, 19 - Water - bath heating module, 20 - Four - way joint, 21 - High - precision cavity measurement module, 2 twenty - two - cavity unit, 2201 - Semiconductor light source, 2202 - Collimating lens, 2203 - Diaphragm, 2204 - First reflector, 2205 - Beam splitter, 2224 - Second reflector, 2206 - First Teflon cavity, 2213 - First high - reflection mirror, 2214 - Second high - reflection mirror, 2210 - First filter, 2222 - First focusing lens, 2212 - First photomultiplier tube, 2207 - First pressure gauge, 2208 - First air - extraction flowmeter, XXXX - First air pump, 2223 - Second Teflon cavity, 2221 - Third high - reflection mirror, 2222 - Fourth high - reflection mirror, 2218 - Second filter, 2219 - Second focusing lens, 2220 - Second photomultiplier tube, 2215 - Second pressure gauge, 2217 - Second air pump, 2216 - Second air - extraction flowmeter, 24 - Temperature control and circulation module. 23 - Signal processing module. Detailed implementation

[0039] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0040] As Figure 1 shown, a multi - channel active nitrogen classification measurement system based on a high - precision cavity includes: an intake module 4, a humidity control module 12, a pyrolysis module, a water - bath heating module 19, a high - precision cavity measurement module 21, a temperature control and circulation module 24, and a signal processing module 23.

[0041] The intake module 4 is used to respectively input the sampled gas into the humidity control module 12 and the pyrolysis module; the intake module 4 is also connected to the high - precision cavity measurement module 21 through the direct sampling tube 7 to directly input the sampled gas into the high - precision cavity measurement module 21; the sampled gas is ambient air or ambient air after filtering and reacting with the gas. The reaction gas contains active nitrogen gases such as nitrogen dioxide, nitric acid, and nitrate esters.

[0042] It should be noted that there is an "XXXX" in the English translation of item which is likely a typo in the original Chinese text. It should be "2209 - First air pump" in the original Chinese.The humidity control module 12 is connected to the intake module 4, where the sampled gas is humidified and its humidity is controlled, and the humidified gas is input into the pyrolysis module.

[0043] The pyrolysis module contains a number of pyrolysis units with different pyrolysis temperatures, which are used to input the gas directly sampled by the intake module 4 and the gas humidified by the humidity control module 12; the pyrolysis units are used to pyrolytically separate nitric acid and nitrate esters in ambient air to generate nitrogen dioxide gas.

[0044] The pyrolysis module is connected to the high-precision cavity measurement module 21 via a water bath heating module 19, and is used to control the temperature (rapid cooling) of the pyrolyzed gas and then input it into the high-precision cavity measurement module 21; the direct sampling tube 7 is also connected to the high-precision cavity measurement module 21 via the water bath heating module 19, and is used to control the temperature of the directly sampled gas and then input it into the high-precision cavity measurement module 21; the water bath heating module 19 is used to ensure the temperature consistency of all the gases entering the high-precision cavity measurement module 21.

[0045] The high-precision cavity measurement module 21 is used to measure the concentration of nitrogen dioxide gas.

[0046] The signal processing module 23 is used to perform real-time calculation and processing on the optoelectronic signals output by the high-precision cavity measurement module 21 to obtain the concentrations of different types of reactive nitrogen in ambient air.

[0047] The temperature control and circulation module 24 is used to monitor the temperature states of each pyrolysis unit in the pyrolysis module and the water bath heating module 19.

[0048] The detailed structures of each part in the present invention are specifically as follows:

[0049] In the intake module 4, ambient air enters from the input end (sampling port) of the intake pipeline. The intake pipeline is provided with a filter membrane 1 for filtering particulate matter in ambient air. The output end of the intake pipeline is connected to two gas paths through a three-way solenoid valve 2. Among them, the first gas path is provided with an activated carbon tube 3 for filtering reactive gas in ambient air. The first gas path and the second gas path are first merged through a first three-way joint 5, and then respectively connected to a first four-way solenoid valve 8 and a direct sampling tube 7 through a second three-way joint 6. The first four-way solenoid valve 8 is respectively connected with a first sampling tube 9, a second sampling tube 10 and a third sampling tube 11, and is connected to the first pyrolysis unit of the pyrolysis module through the first sampling tube 9, and is connected to the first humidity unit and the second humidity unit in the humidity control module 12 through the second sampling tube 10 and the third sampling tube 11 respectively. Heating resistance wires are provided on the entire gas path of the intake module 4 to heat the gas in the entire gas path to remove moisture, which can effectively avoid the influence of water on the measurement of nitric acid.

[0050] The humidity control module 12 includes a first humidity unit and a second humidity unit. Each humidity unit is equipped with a humidity monitor, a humidifier, and a flow meter, which are used to achieve the automatic monitoring and control of the gas humidity, ensuring that the gas humidity always exceeds 70%. By controlling the humidity of the sampled gas, organic peroxy radicals in the pyrolysis products can be effectively removed, preventing them from reacting or recombining with components such as nitrogen oxides and ozone. Thus, a stable and efficient pyrolysis efficiency can be maintained under the background of high concentrations of nitrogen oxides and ozone.

[0051] The pyrolysis module uses an oil bath heating method and includes three pyrolysis units. Among them, the first pyrolysis unit includes a first high-temperature heat-conducting oil 14 and a first spiral spring tube 13 connected to the first sampling tube 9; the second pyrolysis unit includes a second high-temperature heat-conducting oil 16 and a second spiral spring tube 15 connected to the first humidity unit; the third pyrolysis unit includes a third high-temperature heat-conducting oil 18 and a third spiral spring tube 17 connected to the second humidity unit. The high-temperature heat-conducting oil is used to uniformly and stably heat the spiral spring tube, enabling the gas in the spiral spring tube to be fully heated and dissociated.

[0052] The water bath heating module 19 controls the temperature of the output gases of the three pyrolysis units and the output gas of the direct sampling tube 7 simultaneously, ensuring the temperature consistency of the output gases of the three pyrolysis units and the output gas of the direct sampling tube 7, that is, ensuring the temperature consistency of the gas entering the high-precision cavity measurement module 21, so that the gas enters the cavity evenly and smoothly. The water bath heating module 19 merges and connects the output ends of the three pyrolysis units to the high-precision cavity measurement module 21 through a four-way joint 20.

[0053] The high-precision cavity measurement module 21 includes two cavity units 22 with the same structure. Among them, the first cavity unit is connected to the pyrolysis unit; the second cavity unit is connected to the intake module 4.

[0054] In the high-precision cavity measurement module 21, a semiconductor light source 2201 emits broadband light in the absorption band of the gas to be measured. A collimating lens 2202 converts the divergent light emitted by the semiconductor light source 2201 into parallel light. A diaphragm 2302 filters out the edge stray light from the parallel light output by the collimating lens 2202 and outputs the parallel light with the edge stray light filtered to a first reflecting mirror 2204. The first reflecting mirror 2204 deflects the optical path by 90° and then outputs it to a beam splitter 2205. After the beam splitter 2205 splits the optical path, one beam of light enters the first cavity unit, and the other beam of light enters the second cavity unit after being reflected by a second reflecting mirror 2224.

[0055] The first cavity unit includes: a No. 1 Teflon cavity 2206, a No. 1 high-reflection mirror 2213 and a No. 2 high-reflection mirror 2214 that cause the broadband light input into the cavity to be reflected multiple times in the cavity, a No. 1 optical filter 2210 for filtering out redundant bands from the broadband light (and ambient light) output from the cavity, a No. 1 focusing lens 2222 for focusing the broadband light after filtering out the redundant bands, a No. 1 photomultiplier tube 2212 for performing photoelectric conversion on the focused broadband light to obtain a first photoelectric signal, a No. 1 pressure gauge 2207 for real-time monitoring of the internal pressure of the cavity, a No. 1 air pump 2209 for pumping the output gas of the pyrolysis module to the cavity, and a No. 1 exhaust gas flowmeter 2208 for controlling the pumping speed of the No. 1 air pump 2209.

[0056] The second cavity unit includes: a No. 2 Teflon cavity 2223, a No. 3 high-reflection mirror 2221 and a No. 4 high-reflection mirror 2222 that cause the broadband light input into the cavity to be reflected multiple times in the cavity, a No. 2 optical filter 2218 for filtering out redundant bands from the broadband light (and ambient light) output from the cavity, a No. 2 focusing lens 2219 for focusing the broadband light after filtering out the redundant bands, a No. 2 photomultiplier tube 2220 for performing photoelectric conversion on the focused broadband light to obtain a second photoelectric signal, a No. 2 pressure gauge 2215 for real-time monitoring of the internal pressure of the cavity, a No. 2 air pump 2217 for pumping the output gas of the intake module 4 to the cavity, and a No. 2 exhaust gas flowmeter 2216 for controlling the pumping speed of the No. 2 air pump 2217.

[0057] A heating resistance wire is provided on the cavity of each cavity unit 22 for heating the gas in the cavity to remove moisture and eliminate the influence of water vapor on the high-reflection mirror, so that additional protective gas purging is not required.

[0058] The temperature control and circulation module 24 includes four temperature control units for respectively controlling the temperatures of three pyrolysis units and the water bath heating module 19. Each temperature control unit has a corresponding temperature control device and a pump for pumping and circulating the liquid. Among them, the three pyrolysis units and the water bath heating module 19 can share one temperature control device.

[0059] The signal processing module 23 includes a signal acquisition unit, a processor and signal display software for performing signal acquisition and processing on the first photoelectric signal and the second photoelectric signal output by the high-precision cavity measurement module 21.

[0060] The test principle of a multi-channel active nitrogen classification measurement system based on a high-precision cavity according to the present invention is specifically as follows:

[0061] (1) When it is necessary to measure the concentration of reactive nitrogen in ambient air, the gas path below the three-way solenoid valve 2, i.e., the second gas path, is opened. After the ambient air is filtered by the filter membrane 1 to remove particulate matter, it then enters the first sampling tube 9, the second sampling tube 10, or the third sampling tube 11 through the second gas path, the first three-way joint 5, the second three-way joint 6, and the first four-way solenoid valve 8, and also enters the direct sampling tube 7 through the first three-way joint 5 and the second three-way joint 6. The decay times τ 11 , τ 12 , τ 13 are measured when the gas output from the input of the first Teflon cavity 2206 to the output of the first spiral tube 13, the output of the second spiral tube 15, and the output of the third spiral tube 17, and the decay time τ2 when there is a gas to be measured in the second Teflon cavity 2223.

[0062] When it is necessary to measure the system background, the gas path above the three-way solenoid valve 2, i.e., the first gas path, is opened. After the ambient air is filtered by the filter membrane 1 to remove particulate matter and then filtered by the activated carbon tube 3 on the first gas path to remove reactive gases, it then enters the first sampling tube 9, the second sampling tube 10, or the third sampling tube 11 through the first three-way joint 5, the second three-way joint 6, and the first four-way solenoid valve 8, and also enters the direct sampling tube 7 through the first three-way joint 5 and the second three-way joint 6. The background decay time τ 10 is measured when there is no gas to be measured (i.e., the ambient air after filtering reactive gases) in the first Teflon cavity 2206, and the background decay time τ 20 when there is no gas to be measured in the second Teflon cavity 2223.

[0063] Due to the existence of solid particulate matters such as dust and PM2.5 in ambient air, if the solid particulate matters adhere to the reflective surface of the high-reflectivity mirror of the high-precision cavity measurement module 21, it will cause the reflectivity of the high-reflectivity mirror to gradually decrease. Therefore, the present invention provides a filter membrane 1 at the sampling port of ambient air, which can greatly reduce the occurrence of such situations.

[0064] Through the design of the intake module of the present invention, the switching measurement of the reactive nitrogen concentration and the system background can be realized, and at the same time, the influence of solid particulate matters such as dust on the measurement accuracy of the system is avoided.

[0065] (2) When pyrolytic separation of the gas is required, the first high-temperature heat-conducting oil 14, the second heat-conducting oil 16, and the third high-temperature heat-conducting oil 18 in the pyrolysis module are heated to 600 °C, 360 °C, and 180 °C respectively by the temperature control devices in the temperature control and circulation module 24, so that nitric acid and nitrate esters (peroxynitrate and alkyl nitrate) in the ambient atmosphere will be completely pyrolyzed into nitrogen dioxide gas in the first spiral tube 13; peroxynitrate and alkyl nitrate in the ambient atmosphere are completely pyrolyzed into nitrogen dioxide gas in the second spiral tube 15, while nitric acid is not pyrolyzed; peroxynitrate in the ambient atmosphere is completely pyrolyzed into nitrogen dioxide gas in the third spiral tube 17, while nitric acid and alkyl nitrate are not pyrolyzed.

[0066] (3) Before the gas in the first spiral tube 13, the second spiral tube 15, the third spiral tube 17, and the direct sampling tube 7 enters the high-precision cavity measurement module 21, it will be temperature-controlled by the water bath heating module 19 and maintained at the same constant temperature, which can effectively avoid the influence of turbulence on the gas concentration measurement and reduce the jitter of the measurement results.

[0067] (4) The high-precision cavity measurement module 21 uses cavity ring-down spectroscopy technology to measure the nitrogen dioxide gas concentrations in the first spiral tube 13, the second spiral tube 15, the third spiral tube 17, and the direct sampling tube 7 respectively. Among them, the nitrogen dioxide gas concentrations in the first spiral tube 13, the second spiral tube 15, and the third spiral tube 17 are measured by switching through the first four-way solenoid valve 8. The calculation formulas for the nitrogen dioxide gas concentrations in each pipeline are as follows:

[0068]

[0069] Among them, C 11 、C 12 、C 13 、C2 are the nitrogen dioxide gas concentrations in the first spiral tube 13, the second spiral tube 15, the third spiral tube 17, and the direct sampling tube 7 respectively; c is the speed of light; L1 is the ratio of the cavity length of the first Teflon cavity 2206 to the single-pass absorption optical path length of the gas in the cavity, and L2 is the ratio of the cavity length of the second Teflon cavity 2223 to the single-pass absorption optical path length of the gas in the cavity; τ 11 is the ring-down time when the first Teflon cavity 2206 inputs the gas output from the first spiral tube 13, τ 12 is the ring-down time when the first Teflon cavity 2206 inputs the gas output from the second spiral tube 15, τ 13 is the ring-down time when the first Teflon cavity 2206 inputs the gas output from the third spiral tube 17, τ 10 is the background ring-down time when there is no gas to be measured in the first Teflon cavity 2206; τ2 is the ring-down time when there is gas to be measured (i.e., input ambient atmosphere) in the second Teflon cavity 2223, τ 20It is the background decay time when there is no gas to be measured (i.e., the ambient atmosphere after inputting the filtered reaction gas) in the No. 2 Teflon body 2223. In this embodiment, the background τ of the No. 1 Teflon cavity 2206 is measured 10 When measuring, any one of the spiral tube output gases can be selected for measurement, or the output gases of the three spiral tubes can be used for measurement and then the average value is taken.

[0070] Let the concentration of nitric acid in the ambient atmosphere be C H and the concentration of peroxy nitrate be C P and the concentration of alkyl nitrate be C A , then according to C P =C 13 -C2, C A =C 12 -C p 、C H =C 11 -C A , the concentration of reactive nitrogen of the corresponding type can be calculated.

[0071] The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A multi-channel active nitrogen classification measurement system based on a high-precision cavity, characterized in that Including: An intake module (4), a humidity control module (12), a pyrolysis module, a water bath heating module (19), a high-precision cavity measurement module (21), and a signal processing module (23); The intake module (4) is used to input the sampled gas into the humidity control module (12) and the pyrolysis module respectively, and directly input the sampled gas into the high-precision cavity measurement module (21) through a direct sampling tube (7); the sampled gas is ambient air or ambient air after filtering the reactive gas; the reactive gas refers to active nitrogen gas; The humidity control module (12) is connected to the intake module (4) and is used to humidify the sampled gas and input the humidified gas into the pyrolysis module; The pyrolysis module contains several pyrolysis units with different pyrolysis temperatures and is used to input the gas directly sampled by the intake module (4) and the gas humidified by the humidity control module (12); the pyrolysis unit is used to pyrolyze and separate the active nitrogen in the ambient air to generate nitrogen dioxide gas; The pyrolysis module is connected to the high-precision cavity measurement module (21) through the water bath heating module (19) and is used to control the temperature of the pyrolyzed gas and then input it into the high-precision cavity measurement module (21); the direct sampling tube (7) is also connected to the high-precision cavity measurement module (21) through the water bath heating module (19) and is used to control the temperature of the directly sampled gas and then input it into the high-precision cavity measurement module (21); The high-precision cavity measurement module (21) is used to measure the concentration of nitrogen dioxide gas; the signal processing module (23) is used to perform real-time calculation and processing on the optoelectronic signal output by the high-precision cavity measurement module (21) to obtain the concentration of different types of active nitrogen in the ambient air.

2. The multi-channel active nitrogen classification measurement system based on a high-precision cavity according to claim 1, wherein A filter membrane (1) for filtering particulate matter in the ambient air is provided at the sampling port of the intake module (4); the intake module (4) includes two gas paths, and an activated carbon tube (3) for filtering the reactive gas in the ambient air is provided on the first gas path; the intake module (4) inputs the sampled gas passing through the first gas path or the second gas path into the humidity control module (12), the pyrolysis module, and the high-precision cavity measurement module (21) respectively.

3. The multi-channel active nitrogen classification measurement system based on a high-precision cavity according to claim 1, characterized in that, The pyrolysis module adopts the method of oil bath heating and includes at least three pyrolysis units; each pyrolysis unit includes high-temperature heat-conducting oil and a spiral spring tube. The high-temperature heat-conducting oil is used to uniformly and stably heat the spiral spring tube so that the gas in the spiral spring tube is fully heated and dissociated; among them, the spiral spring tube of the first pyrolysis unit inputs the gas directly sampled by the intake module (4), and the spiral spring tubes of the second and third pyrolysis units both input the gas humidified by the humidity control module (12).

4. A multi-channel active nitrogen classification measurement system based on a high-precision cavity according to claim 1, wherein The high-precision cavity measurement module (21) includes at least two cavity units (22) with the same structure; among them, the first cavity unit is connected to the pyrolysis unit and is used to input the pyrolyzed gas; the second cavity unit is connected to the intake module (4) and is used to input the directly sampled gas; In the high-precision cavity measurement module (21), a light source emits broadband light in the absorption band of nitrogen dioxide gas. After the broadband light is collimated, stray light is filtered, and then split, it is respectively input into the two cavity units (22).

5. The multi-channel active nitrogen classification measurement system based on a high-precision cavity according to claim 4, wherein The cavity unit (22) includes: a cavity, two high-reflection mirrors that cause the broadband light input into the cavity to be reflected multiple times in the cavity, a filter for filtering out redundant bands from the broadband light output from the cavity, a focusing lens for focusing the broadband light after filtering out the redundant bands, a photomultiplier tube for performing photoelectric conversion on the focused broadband light to obtain a photoelectric signal, a pressure gauge for monitoring the internal pressure of the cavity in real time, an air pump for pumping gas into the cavity, and an extraction flowmeter for controlling the pumping speed of the air pump.

6. The multi-channel active nitrogen classification measurement system based on a high-precision cavity according to claim 1, wherein The system further includes a temperature control and circulation module (24) for controlling the temperature of each pyrolysis unit and the water bath heating module (19).

7. A multi-channel active nitrogen classification measurement method based on a high-precision cavity, characterized in that Using the multi-channel active nitrogen classification measurement system based on a high-precision cavity according to any one of claims 1-6, the measurement principle is: The pyrolysis unit (22) includes three pyrolysis units with different pyrolysis temperatures. Among them, the first pyrolysis unit inputs directly sampled gas and is used to pyrolyze nitric acid, peroxy nitrate, and alkyl nitrate in ambient air into nitrogen dioxide gas; the second pyrolysis unit inputs humidified gas and is used to pyrolyze peroxy nitrate and alkyl nitrate in ambient air into nitrogen dioxide gas, and nitric acid is not pyrolyzed; the third pyrolysis unit inputs humidified gas and is used to pyrolyze peroxy nitrate in ambient air into nitrogen dioxide gas, and nitric acid and peroxy nitrate are not pyrolyzed; The high-precision cavity measurement module (21) measures the concentrations of nitrogen dioxide gas in the output gases of the three pyrolysis units to be C 11 , C 12 , C 13 ; the high-precision cavity measurement module (21) directly measures the concentration of nitrogen dioxide gas in the ambient atmosphere to be C2; Let the concentration of nitric acid in the ambient atmosphere be C H and the concentration of peroxy nitrate be C P and the concentration of alkyl nitrate be C A . According to C P = C 13 - C2, C A = C 12 - C p , C H = C 11 - C A , the concentrations of different types of reactive nitrogen in the ambient atmosphere are calculated.

8. A multi-channel active nitrogen classification measurement method based on a high-precision cavity according to claim 7, characterized in that The calculation method for the concentration of each nitrogen dioxide gas is: where c is the speed of light; L1 and L2 are the ratios of the cavity length of the corresponding cavity to the single-pass absorption optical path length of the gas in the cavity; τ 11 is the decay time when the high-precision cavity measurement module (21) measures the gas output by the first pyrolysis unit; τ 12 is the decay time when the high-precision cavity measurement module (21) measures the gas output by the second pyrolysis unit, τ 13 is the decay time when the high-precision cavity measurement module (21) measures the gas output by the third pyrolysis unit; τ 10 is the background decay time when there is no gas to be measured in the pyrolysis unit; τ2 is the decay time when the high-precision cavity measurement module (21) measures the ambient atmosphere, τ 20 is the background decay time when the high-precision cavity measurement module (21) measures the ambient atmosphere after filtering the reaction gas.

9. A multi-channel active nitrogen classification measurement method based on a high-precision cavity according to claim 7, characterized in that, The pyrolysis temperatures of the first, second, and third pyrolysis units are 600 °C, 360 °C, and 180 °C, respectively.

10. A computer program product, characterized in that, It includes a computer program / instructions, and when the computer program / instructions are executed by a processor, it implements the multi-channel active nitrogen classification measurement method based on a high-precision cavity according to any one of claims 7-9.

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