CN111562228A - Nitrogen dioxide measuring device and measuring method - Google Patents
Nitrogen dioxide measuring device and measuring method Download PDFInfo
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- CN111562228A CN111562228A CN202010546228.6A CN202010546228A CN111562228A CN 111562228 A CN111562228 A CN 111562228A CN 202010546228 A CN202010546228 A CN 202010546228A CN 111562228 A CN111562228 A CN 111562228A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/01—Arrangements or apparatus for facilitating the optical investigation
Abstract
The invention relates to the field of atmospheric pollutant detection, in particular to a nitrogen dioxide measuring device and a measuring method, wherein the nitrogen dioxide measuring device comprises a measuring module, a temperature control module and a control module; the measurement module is used for collecting gas and detecting the concentration of nitrogen dioxide in the collected gas by using an absorption spectroscopy; the temperature control module comprises a first temperature control unit and a second temperature control unit, the first temperature control unit is used for controlling the peripheral temperature of the measurement module, and the second temperature control unit is used for controlling the temperature of the light source of the measurement module; the control module is electrically connected with the measuring module and the temperature control module and is used for controlling the work of the measuring module and the work of the temperature control module. The nitrogen dioxide measuring device provided by the embodiment of the invention is provided with the measuring module to detect the concentration of nitrogen dioxide by adopting an absorption spectroscopy method, and the temperature control module can monitor the peripheral temperature of the measuring module and the temperature of a light source.
Description
Technical Field
The invention relates to the field of atmospheric pollutant detection, in particular to a nitrogen dioxide measuring device and a nitrogen dioxide measuring method.
Background
The nitrogen dioxide is one of main atmospheric pollutants, mainly comes from combustion processes such as traffic, industrial production, biomass combustion and the like, influences regional air quality and atmospheric chemical reaction, and has important significance for research on air quality monitoring and atmospheric chemical reaction by accurately measuring the concentration of the nitrogen dioxide in the atmosphere. In high altitude areas, human activities are significantly reduced, the concentration level of nitrogen dioxide in the atmosphere ranges from several tens of pptv to several pptv, and the environmental temperature fluctuates greatly, requiring high sensitivity and stability of the measurement system. Until now, no reliable measuring device is reported to be used for long-term effective monitoring of the nitrogen dioxide concentration in the high-altitude area, which also restricts the development of related researches in the high-altitude area.
At present, most of conventional nitrogen dioxide measuring devices adopt a chemiluminescence method of reaction of nitric oxide and ozone, such as a 42i type nitrogen oxide analyzer of American Sammerfei company, an nCLD type nitrogen oxide analyzer of Switzerland ECO Physics company, an EC9841 type nitrogen oxide analyzer of Australian ECOTECH company, and nitrogen oxide analyzers proposed by China's light gathering science and Wuhan sky rainbow and other companies. Although such devices are widely used for business observation, the measurement of nitrogen dioxide gas based on chemiluminescence method is affected by factors such as conversion or titration efficiency, and interference of other nitrogen-containing substances in the atmosphere, and the detection sensitivity and accuracy are insufficient, so that the monitoring requirements of high altitude areas cannot be met.
Recently developed high-sensitivity resonant cavity spectroscopic techniques, such as cavity ring-down absorption spectroscopy, cavity attenuation phase shift spectroscopy and cavity enhanced absorption spectroscopy, can achieve direct measurement of nitrogen dioxide concentration, have high detection sensitivity and are not affected by conversion or titration efficiency. For example, nitrogen oxide measurement systems developed based on cavity ring-down absorption spectroscopy (environ. Sci. Technol.2009, 43, 7831-. The detection sensitivity of the above systems is typically obtained in low altitude laboratory evaluations and does not reflect the instrument performance of the actual operating environmental conditions. In addition, the above system does not take into account the influence of the fluctuation of the ambient temperature, and therefore it is also difficult to satisfy accurate measurement of nitrogen dioxide in a high altitude area where the fluctuation of the diurnal temperature difference is large.
Therefore, the conventional nitrogen dioxide measuring device based on the chemiluminescence method has the problems of insufficient sensitivity and the like, and the conventional nitrogen dioxide measuring device based on the high-sensitivity resonant cavity technology has the problems of environmental temperature change influence and the like, so that the long-term accurate monitoring of nitrogen dioxide in a high-altitude area cannot be met, and therefore a high-sensitivity nitrogen dioxide measuring device applied to the high-altitude area is urgently needed.
Disclosure of Invention
The embodiment of the invention aims to provide a nitrogen dioxide measuring device, and aims to solve the problems that the conventional nitrogen dioxide measuring device based on a chemiluminescence method is insufficient in sensitivity and the like, and the conventional nitrogen dioxide measuring device based on a high-sensitivity resonant cavity technology has the problems of influence of environmental temperature change and the like, so that the long-term accurate monitoring of nitrogen dioxide in a high-altitude area cannot be met, and the problem that the high-sensitivity nitrogen dioxide measuring device applied to the high-altitude area is urgently needed.
The embodiment of the invention is realized in such a way that the nitrogen dioxide measuring device comprises a measuring module, a temperature control module and a control module;
the measurement module is used for collecting gas and detecting the concentration of nitrogen dioxide in the collected gas by using an absorption spectroscopy;
the temperature control module comprises a first temperature control unit and a second temperature control unit, the first temperature control unit is used for controlling the peripheral temperature of the measurement module, and the second temperature control unit is used for controlling the temperature of the light source of the measurement module;
the control module is electrically connected with the measuring module and the temperature control module and is used for controlling the work of the measuring module and the work of the temperature control module.
In another embodiment of the present invention, there is also provided a nitrogen dioxide measuring method applied to the nitrogen dioxide measuring apparatus according to any one of the embodiments of the present invention, the nitrogen dioxide measuring method including the steps of:
monitoring the peripheral temperature of the measuring module and the temperature of the light source by using a temperature control module;
obtaining background gas, removing nitrogen dioxide in the background gas and measuring a spectrum signal of the background gas after the nitrogen dioxide is removed;
acquiring a sample gas and measuring a spectral signal of the sample gas;
determining a nitrogen dioxide absorption coefficient according to the spectral signal of the background gas and the spectral signal of the sample gas;
and determining the nitrogen dioxide concentration of the sample gas according to the nitrogen dioxide absorption coefficient.
The nitrogen dioxide measuring device provided by the embodiment of the invention can detect the concentration of nitrogen dioxide by adopting an absorption spectrum method through arranging the measuring module, and the method is more suitable for detecting low-concentration nitrogen dioxide than a chemiluminescence detection method; peripheral temperature of the measuring module and light source temperature can be monitored by the temperature control module, so that influence of temperature fluctuation of high-altitude areas on measuring precision is eliminated, and the light source can be stabilized by monitoring the light source temperature, so that detection precision is provided. The method is suitable for plateau areas with large temperature fluctuation and low nitrogen dioxide concentration.
Drawings
Fig. 1 is a structural diagram of a nitrogen dioxide measuring device according to an embodiment of the present invention;
fig. 2 is a graph showing the measurement result of the concentration of atmospheric nitrogen dioxide in a high-altitude area by using a nitrogen dioxide measurement device according to an embodiment of the present invention;
fig. 3 is a diagram illustrating the result of evaluating the detection sensitivity of a nitrogen dioxide measuring device in a high altitude area according to an embodiment of the present invention.
In the drawings: 101. a light source unit; 102. a front optical fiber; 102', a rear optical fiber, 103, a front collimating lens; 103', a rear collimating lens; 104. a front high reflectance lens; 104', a rear high-reflectivity lens; 105. a broadband optical filter; 106. a spectrometer; 107. a cavity; 108. an air chamber; 109, an air inlet; 109', an air outlet; 200. a background gas inlet pipe; 201. a sample gas inlet pipe; 202. a nitrogen dioxide adsorber; 203. a three-way electromagnetic valve; 204. a particle filter; 205. a barometer; 206. a mass flow meter; 207. a vacuum pump; 301. a data acquisition control unit; 401. a temperature controller; 402. a heating layer; 403. a thermocouple; 404. a heat radiation fan; 501. and (4) a box body.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Specific implementations of the present invention are described in detail below with reference to specific embodiments.
As shown in fig. 1, which is a structural diagram of a nitrogen dioxide measuring device provided in an embodiment of the present invention, the nitrogen dioxide measuring device includes a measuring module, a temperature control module, and a control module;
the measurement module is used for collecting gas and detecting the concentration of nitrogen dioxide in the collected gas by using an absorption spectroscopy;
the temperature control module comprises a first temperature control unit and a second temperature control unit, the first temperature control unit is used for controlling the peripheral temperature of the measurement module, and the second temperature control unit is used for controlling the temperature of the light source of the measurement module;
the control module is electrically connected with the measuring module and the temperature control module and is used for controlling the work of the measuring module and the work of the temperature control module.
In the embodiment of the invention, the measuring module is used for detecting the concentration of nitrogen dioxide after collecting gas, and the measuring module provided by the invention is used for detecting the concentration of nitrogen dioxide by using an absorption spectrum method, is not influenced by interference factors such as conversion or titration efficiency and other nitrogen-containing substances in the atmosphere, and can obtain higher detection precision. It is understood that the absorption spectroscopy in the embodiment of the present invention is a method for determining the content of nitrogen dioxide in a sample gas by measuring and analyzing the spectrum of light absorbed by nitrogen dioxide. In the embodiment of the present invention, the gas may be a specific gas to be detected, and may also be air in any environment, which is not particularly limited in the embodiment of the present invention.
In the embodiment of the invention, the temperature control module is arranged, so that the peripheral temperature of the measurement module can be monitored on one hand, the temperature of the light source can be monitored on the other hand, and the detection precision can be improved. It should be noted that the monitoring in the embodiment of the present invention refers to monitoring and controlling, the monitoring refers to collecting the temperature, and the controlling refers to outputting a control signal to heat or cool so as to stabilize the temperature in a relatively wide range. The monitoring of the temperature around the measuring module refers to monitoring the temperature of the area where the main measuring part of the measuring module is located, so that the influence of temperature fluctuation on the work of the main measuring part is avoided, the main measuring part of the measuring module works in an environment with relatively constant temperature, and meanwhile, the influence of the temperature on the working performance of elements in the measuring process is reduced. The scheme of the invention improves the detection accuracy by at least two aspects.
In the embodiment of the present invention, the control module is used for controlling the operation of the measurement module and the temperature control module, and the control module may include corresponding hardware and system software.
In the embodiment of the present invention, the measurement module, the temperature control module, and the control module may be structurally integrated with each other, for example, disposed in a box 501 to form a whole, and the corresponding hardware of each module is fixed in the box 501 by being directly or indirectly connected to the inner wall of the box 501. This is an optional specific implementation manner, and the embodiment of the present invention is not particularly limited thereto.
The nitrogen dioxide measuring device provided by the embodiment of the invention can detect the concentration of nitrogen dioxide by adopting an absorption spectrum method through arranging the measuring module, and the method is more suitable for detecting low-concentration nitrogen dioxide than a chemiluminescence detection method; peripheral temperature of the measuring module and light source temperature can be monitored by the temperature control module, so that influence of temperature fluctuation of high-altitude areas on measuring precision is eliminated, and the light source can be stabilized by monitoring the light source temperature, so that detection precision is ensured. The method is suitable for plateau areas with large temperature fluctuation and low nitrogen dioxide concentration.
In one embodiment of the present invention, the measurement module includes a gas collection unit, an optical resonance unit, a light source unit 101, and a spectrum detection unit;
the acquisition unit is connected with the optical resonance unit and is used for conveying gas to the optical resonance unit;
the optical resonance unit is used for irradiating the gas;
the light source unit 101 is connected with one end of the optical resonance unit and used for providing a light source for the optical resonance unit;
the spectrum detection unit is connected with the other end of the optical resonance unit and used for acquiring the spectrum of the light passing through the optical resonance unit and determining the concentration of the nitrogen dioxide of the gas to be detected according to the spectrum.
In the embodiment of the present invention, the gas collection unit is used for collecting gas, and it should be understood that collection herein does not refer to a process of obtaining a specific gas from an environment, but refers to a process of delivering air in the environment or a given specific gas into the optical resonance unit, and refers to a delivery process.
In the embodiment of the present invention, the optical resonance unit is a unit which generates an absorption signal by the action of gas and light, and it should be understood that generating the absorption signal herein does not mean that the optical resonance unit itself generates the absorption signal, but means that a subsequent unit module performs spectrum acquisition and analysis on the light after passing through the optical resonance unit to obtain the absorption signal, and the direct action of the optical resonance unit is to make nitrogen dioxide absorb the light. The light source unit 101 is connected to one end of the optical resonance unit, and the connection here refers to optical path connection, and may be direct irradiation or connection through a light guide optical path such as an optical fiber, and includes a front optical fiber 102 and a rear optical fiber 102' as shown in fig. 1. This is an optional specific implementation manner, and the embodiment of the present invention is not particularly limited thereto.
In the embodiment of the invention, the spectrum detection unit is used for collecting the absorbed spectrum and analyzing and processing the spectrum to determine the nitrogen dioxide concentration of the gas to be detected.
In this embodiment of the present invention, the spectrum detection unit may include a spectrometer 106 and a spectrum analysis processing unit, in this embodiment of the present invention, the spectrum analysis processing unit is configured to process and analyze the spectrum signal to determine the content of nitrogen dioxide in the sample gas, the spectrum analysis processing unit may be built in the nitrogen dioxide measurement device provided in any one embodiment of the present invention, or may be an external device, such as various types of computers, and the like, communicatively connected to the nitrogen dioxide measurement device, and this is not specifically limited in this embodiment of the present invention.
The nitrogen dioxide measuring device provided by the embodiment of the invention collects the measured gas through the gas collecting unit, enables the gas to interact with the light through the optical resonance unit, and performs spectrum collection analysis on the absorbed light through the spectrum detecting unit to obtain the nitrogen dioxide concentration of the measured gas, so that the method is not influenced by conversion or titration efficiency, and the detection precision can be improved.
In one embodiment of the invention, the collection unit comprises an intake subunit and an exhaust subunit;
the air inlet subunit comprises a three-way electromagnetic valve 203, a particle filter 204 and a nitrogen dioxide adsorber 202; two inlets of the three-way electromagnetic valve 203 are respectively connected with a background gas inlet pipe 200 and a sample gas inlet pipe 201, and the background gas inlet pipe 200 is connected with the nitrogen dioxide adsorber 202; the outlet of the three-way electromagnetic valve 203 is connected with the inlet of the particle filter 204 through a pipeline, and the outlet of the particle filter 204 is connected with the air inlet 109 of the optical resonance unit;
the exhaust subunit comprises a barometer 205, a mass flow meter 206 and a vacuum pump 207 which are sequentially connected through a pipeline, and is connected with the air outlet 109' of the optical resonance unit.
In the embodiment of the invention, the air inlet subunit is used for collecting the gas to be detected, the air inlet subunit comprises a three-way electromagnetic valve 203 and a particle filter 204, and two inlets of the three-way electromagnetic valve 203 can be respectively used for collecting background gas and collecting the sample gas to be detected. In the embodiment of the present invention, it is understood that the three-way solenoid valve 203 is only a specific implementation manner, and elements similar or equivalent to the three-way solenoid valve 203 may be substituted for the three-way solenoid valve. In the embodiment of the present invention, the air inlet pipe includes a background gas inlet pipe 200 and a sample gas inlet pipe 201, the background gas inlet pipe 200 is connected to a nitrogen dioxide adsorber 202, and the nitrogen dioxide adsorber 202 is used to remove nitrogen dioxide in the entering gas to obtain the background gas, and may be implemented by using activated carbon.
In the embodiment of the present invention, the exhaust subunit is used for exhausting the gas in the optical resonance unit, and comprises a gas pressure meter 205, a mass flow meter 206 and a vacuum pump 207, wherein the gas pressure meter 205 is used for monitoring the gas pressure in the optical resonance unit to obtain a gas pressure more favorable for optical resonance; the mass flow meter 206 can accurately meter the flow rate of the gas; the vacuum pump 207 is used for pumping to drive the gas flow, so that the external gas enters the optical resonance unit and the gas in the optical resonance unit is exhausted. It will be appreciated that in embodiments of the invention, both the inlet and exhaust sub-units are powered by the vacuum pump 207.
The nitrogen dioxide measuring device provided by the embodiment of the invention can convey gas into the optical resonance unit or extract the gas from the optical resonance unit by arranging the acquisition unit, can measure the gas pressure and flow of the gas, and is convenient for controlling the gas quantity and the gas pressure.
In an embodiment of the present invention, the optical resonance unit includes a cavity 107, a gas chamber 108 is disposed in the cavity 107, a gas inlet 109 and a gas outlet 109 'are respectively disposed on side walls of two ends of the gas chamber 108, a front high-reflectivity lens 104 is disposed at a front end of the gas chamber 108, and a rear high-reflectivity lens 104' is disposed at a rear end of the gas chamber 108;
a front collimating lens 103 is disposed at one end of the cavity 107, a rear collimating lens 103 ' is disposed at the rear end, a broadband optical filter 105 is disposed between the rear collimating lens 103 ' and the rear high-reflectivity lens 104 ', and the front collimating lens 103, the front high-reflectivity lens 104, the air chamber 108, the rear high-reflectivity lens 104 ', the broadband optical filter 105 and the rear collimating lens 103 ' are coaxially arranged.
In the embodiment of the present invention, both chamber 107 and air chamber 108 may be provided with a cylindrical hollow structure, preferably, an elongated tubular structure. The gas chamber 108 may be made of metal or teflon, and preferably, teflon material. The front end of the cavity 107 is provided with a front collimating lens 103, the rear end is provided with a rear collimating lens 103 ', and light emitted by the light source enters the cavity 107 through the front collimating lens 103, firstly passes through the air chamber 108, and then irradiates out of the cavity 107 through the rear collimating lens 103'. The front collimating lens 103 is used for collimating the light emitted by the light source into parallel light, and the rear collimating lens 103' is used for collecting the light which passes through the gas chamber 108 and then passes through the broadband filter 105. The front collimating lens 103 and the rear collimating lens 103' are preferably achromatic lenses, and the broadband filter 105 is preferably a band pass filter.
In the embodiment of the present invention, in the cavity 107, the front end of the gas chamber 108 is provided with the front collimating lens 103, the rear end is provided with the rear collimating lens 103 ', the broadband filter 105 is arranged between the rear collimating lens 103 ' and the rear high-reflectivity lens 104 ', and the front collimating lens 103, the front high-reflectivity lens 104, the gas chamber 108, the rear high-reflectivity lens 104 ', the broadband filter 105 and the rear collimating lens 103 ' are coaxially arranged in sequence along the irradiation direction of light.
In the nitrogen dioxide measuring device provided by the embodiment of the invention, the optical resonance unit comprises a cavity 107 and a gas chamber 108 arranged in the cavity 107, laser sequentially passes through the front collimating lens 103, the front high-reflectivity lens 104, the gas chamber 108, the rear high-reflectivity lens 104 ', the broadband optical filter 105 and the rear collimating lens 103', the scheme of the invention adopts an absorption spectrum method to detect the concentration of nitrogen dioxide, and the nitrogen dioxide measuring device is not influenced by conversion or titration efficiency and can improve the detection precision.
In one embodiment of the present invention, the length of the gas cell 108 is determined by the radius of curvature of the front high reflectivity lens 104 or the rear high reflectivity lens 104'.
In the embodiment of the present invention, the curvature radius of the front high-reflectivity lens or the rear high-reflectivity lens is preferably 1 meter, and the length of the air chamber 108 is (0.99-1) meter, and is preferably 0.996 meter.
The length of the air chamber 108 in the nitrogen dioxide measuring device provided by the embodiment of the invention is 0.996 m, so that higher detection precision can be obtained.
In one embodiment of the present invention, the first temperature control unit comprises a box 501, a heating layer 402 and a thermocouple 403 are arranged on the inner wall of the box 501, and the heating layer 402 and the thermocouple 403 are electrically connected with a temperature controller 401;
the temperature controller 401 is electrically connected to the control module.
In the embodiment of the present invention, optionally, the box 501 is configured as a rectangular parallelepiped or a cube, and the cavity 107 or the gas chamber 108 is located at the center of the box 501; further, the distance between chamber 107 or chamber 108 and the wall of box 501 is approximately equal, so that the temperature of each part of chamber 107 or chamber 108 is more uniform.
In the embodiment of the present invention, the material of the case 501 is not particularly limited; the inner wall of the box body 501 is provided with the heating layer 402 and the thermocouple 403, the heating layer 402 can control the internal temperature of the box body 501, the thermocouple 403 can collect the internal temperature of the box body 501, and the temperature controller 401 can control the heating layer 402 according to the temperature collected by the thermocouple 403.
The first temperature control unit of the nitrogen dioxide measuring device provided by the embodiment of the invention comprises a box body 501, a heating layer 402 and a thermocouple 403, and the first temperature control unit can be used for collecting and monitoring the peripheral temperature of the measuring module, so that the interaction of light and gas can be generated in a relatively constant environment, the influence of temperature fluctuation on gas absorption can be reduced, and the detection precision is improved.
In an embodiment of the present invention, a heat dissipation fan 404 is further disposed on a wall surface of the box 501, and the heat dissipation fan 404 is electrically connected to the temperature controller 401.
In the embodiment of the present invention, one or more heat dissipation fans 404 may be provided, and through the arrangement of the heat dissipation fans 404, air in the box 501 may flow to exchange with outside air, and when the temperature is too high, the air may be used for cooling.
The nitrogen dioxide measuring device provided by the embodiment of the invention is also provided with the cooling fan 404, and the cooling fan 404 is matched with the heating layer 402 or the thermocouple 403, so that the temperature in the box body 501 can be monitored.
In one embodiment of the present invention, the second temperature control unit includes a substrate, a temperature sensor, and a semiconductor cooling plate;
the light source of the measuring module is arranged on the substrate, the substrate is provided with a mounting groove, and the temperature sensor is connected with the substrate through the mounting groove and used for detecting the temperature of the substrate;
the back surface of the substrate is tightly attached to the cold surface of the semiconductor refrigerating sheet;
the temperature sensor and the semiconductor refrigeration piece are electrically connected with the control module.
In the embodiment of the present invention, the substrate may be made of a metal material to facilitate heat dissipation, and optionally, an aluminum material may be used. The light source is arranged on the substrate, and the light source and the substrate can be connected by adopting a screw connection mode, a welding mode and the like. Be provided with the mounting groove on the base plate, be provided with temperature sensor in the mounting groove and be used for gathering the temperature of base plate, the temperature of acquireing the light source during operation is actual. The back of the substrate is provided with a semiconductor refrigeration piece opposite to the light source installation position, the semiconductor refrigeration piece and the substrate can be connected in a screw connection mode or a welding mode, and the cold surface of the semiconductor refrigeration piece is opposite to the substrate.
In the embodiment of the present invention, preferably, a heat sink is disposed on a hot surface of the semiconductor chilling plate; the base plate, the temperature sensor, the semiconductor refrigeration piece and the radiating fin are coated with heat-conducting silicone grease at the contact part of the base plate, the temperature sensor, the semiconductor refrigeration piece and the radiating fin.
The second temperature control unit in the nitrogen dioxide measuring device provided by the embodiment of the invention comprises a substrate, a temperature sensor and a semiconductor refrigerating sheet, and the temperature of the light source can be monitored through the arrangement, so that the light source emits stable light meeting the requirement, and the influence of the fluctuation of the light source on the detection precision is avoided.
The nitrogen dioxide measuring device provided by the embodiment of the invention can detect the concentration of nitrogen dioxide by adopting an absorption spectrum method through arranging the measuring module, and the method is more suitable for detecting low-concentration nitrogen dioxide than a chemiluminescence detection method; peripheral temperature of the measuring module and light source temperature can be monitored by the temperature control module, so that influence of temperature fluctuation of high-altitude areas on measuring precision is eliminated, and the light source can be stabilized by monitoring the light source temperature, so that detection precision is ensured. The method is suitable for plateau areas with large temperature fluctuation and low nitrogen dioxide concentration.
The embodiment of the invention also provides a nitrogen dioxide measuring method, and by applying the nitrogen dioxide measuring device provided by any one embodiment of the invention, the nitrogen dioxide measuring method comprises the following steps:
monitoring the peripheral temperature of the measuring module and the temperature of the light source by using a temperature control module;
obtaining background gas, removing nitrogen dioxide in the background gas and measuring a spectrum signal of the background gas after the nitrogen dioxide is removed;
acquiring a sample gas and measuring a spectral signal of the sample gas;
determining a nitrogen dioxide absorption coefficient according to the spectral signal of the background gas and the spectral signal of the sample gas;
and determining the nitrogen dioxide concentration of the sample gas according to the nitrogen dioxide absorption coefficient.
The following is a description of a specific embodiment:
as shown in fig. 2, the nitrogen dioxide measuring device provided by the embodiment of the present invention is used for online measurement of atmospheric nitrogen dioxide concentration in a high altitude area, and the specific process is as follows: the ambient atmosphere is pumped into the gas chamber 108 in the cavity 107 through the vacuum pump 207, the three-way electromagnetic valve 203 controls the switching of the ambient atmosphere and the background gas, the barometer 205 monitors the air pressure in the gas chamber 108, the mass flow meter 206 controls the flow of the gas, the spectrometer 106 obtains a broadband absorption spectrum of the gas to be measured, a high-resolution absorption cross section is convoluted with a spectrometer instrument function to obtain a theoretical reference absorption cross section, and then least square fitting is performed on the absorption coefficient obtained through calculation to obtain the concentration of the nitrogen dioxide gas. Because the influence of atmospheric pressure change on the absorption section can be ignored, the measuring system and the method can accurately obtain the concentration of the nitrogen dioxide in the high-altitude area. The data processing flow comprises the following steps:
step (1), the three-way electromagnetic valve 203 is switched to communicate the background gas inlet pipe 200 and the nitrogen dioxide adsorber 202 to remove the nitrogen dioxide gas in the background gas, the background gas enters the gas chamber 108 after passing through the particle filter 204, and the spectrometer 106 measures and obtains the spectrum signal I of the background gas with the wave band of 445 and 465nm0(λ), where λ is the wavelength.
And (2) switching and communicating a sample gas inlet pipe 201 by a three-way electromagnetic valve 203, wherein the sample gas contains nitrogen dioxide gas, the sample gas enters a gas chamber 108 after passing through a particle filter 204, and a spectrum signal I (lambda) of the sample gas with a wave band of 445 and 465nm is obtained by measurement of a spectrometer 106, wherein the lambda is the wavelength.
Step (3), according to the steps (1) to (2), knowing the distance d between the front high-reflectivity lens 104 and the rear high-reflectivity lens 104', calibrating the reflectivity R (λ) of the high-reflectivity lens by using high-purity (> 99.999%) nitrogen and carbon dioxide gas:
wherein, IN2(lambda) and ICO2(lambda) are the measured spectral signals of high purity nitrogen and carbon dioxide gas respectively,
and
known rayleigh scattering cross sections of nitrogen gas and carbon dioxide gas respectively, lambda being the wavelength; the high reflectance lens has a reflectance of R (λ).
And (4) measuring the spectral signal I of the background gas according to the steps (1) to (3)0(λ) and a spectral signal I (λ) of the ambient atmosphere, and an absorption coefficient b of the ambient atmosphere is obtained by calculation using the following equationabs(λ)：
Where λ is the wavelength.
Step (5), according to the steps (1) to (4), at the wave band of 445-465nm, the absorption of other gases except the nitrogen dioxide gas in the sample gas can be ignored, and then the absorption coefficient b of the sample gasabsThe relationship between (λ) and the concentration n of nitrogen dioxide can be expressed as the following equation:
babs(λ)＝nσ(s+tλ)+P(λ)；
wherein n σ (s + t λ) is an absorption coefficient of the nitrogen dioxide gas, n is a concentration of the nitrogen dioxide gas, and σ is an absorption cross section of the known nitrogen dioxide gas; s and t represent the shift and stretch of the spectral line positions, respectively, and P (λ) is the spectral shift caused by LED source instability and spectrometer background drift. And carrying out nonlinear least square fitting on the measured spectrum signal to obtain the concentration of the nitrogen dioxide gas in the sample gas.
The detection sensitivity of the nitrogen dioxide measuring device provided by the invention is 10pptv (120 seconds sampling time) in the evaluation result of the high altitude area.
As shown in fig. 3, the detection sensitivity of the nitrogen dioxide measuring device provided by the present invention was evaluated in a high-altitude area using a long-time measurement of filtered air, which is a dry gas from which nitrogen dioxide is removed.
The specific process comprises the following steps: filtered air is pumped into the air chamber 108 of the cavity 107 through the vacuum pump 207, the three-way electromagnetic valve 203 controls the switching of sample gas and background gas, the barometer 205 monitors the air pressure in the air chamber 108, the mass flow meter 206 controls the flow of the gas, the spectrometer 106 measures to obtain the broadband absorption spectrum of the gas to be measured, the high-resolution absorption cross section is convoluted with a spectrometer instrument function to obtain a theoretical reference absorption cross section, and then least square fitting is performed on the absorption coefficient obtained through calculation to obtain the concentration of the nitrogen dioxide gas. The specific calculation method is the same as the above specific example, except that the filtered air to be measured is a dry gas from which nitrogen dioxide is removed, and the obtained measured value of the nitrogen dioxide gas concentration fluctuates around the zero point, and the fluctuation can reflect the degree of the comprehensive influence of the factors such as noise, interference and drift on the measured value of the nitrogen dioxide measuring device. Since the Allan variance method reflects the stability of the device over time, it can be used to characterize the detection sensitivity of the device. As shown in fig. 3, the average value of nitrogen dioxide was 6pptv, the standard deviation value was 24pptv, and the evaluation values of the variances of alan at the sampling times of 30 seconds and 120 seconds were 19pptv and 10pptv, respectively, as measured by filtered air at about 266 minutes, so that the detection sensitivity of the nitrogen dioxide measuring device provided by the present invention was evaluated at 10pptv (120 second sampling time) in the high altitude area.
The evaluation result shows that the nitrogen dioxide measuring device provided by the invention can accurately measure the concentration of atmospheric nitrogen dioxide in a high-altitude area.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (10)
1. The nitrogen dioxide measuring device is characterized by comprising a measuring module, a temperature control module and a control module;
the measurement module is used for collecting gas and detecting the concentration of nitrogen dioxide in the collected gas by using an absorption spectroscopy;
the temperature control module comprises a first temperature control unit and a second temperature control unit, the first temperature control unit is used for controlling the peripheral temperature of the measurement module, and the second temperature control unit is used for controlling the temperature of the light source of the measurement module;
the control module is electrically connected with the measuring module and the temperature control module and is used for controlling the work of the measuring module and the work of the temperature control module.
2. The nitrogen dioxide measurement device of claim 1, wherein the measurement module comprises a gas collection unit, an optical resonance unit, a light source unit, and a spectrum detection unit;
the gas acquisition unit is connected with the optical resonance unit and is used for conveying gas to the optical resonance unit;
the optical resonance unit is used for irradiating the gas;
the light source unit is connected with one end of the optical resonance unit and used for providing a light source for the optical resonance unit;
the spectrum detection unit is connected with the other end of the optical resonance unit and used for acquiring the spectrum of the light passing through the optical resonance unit and determining the concentration of the nitrogen dioxide of the gas to be detected according to the spectrum.
3. The nitrogen dioxide measurement device of claim 2, wherein the gas collection unit comprises an intake subunit and an exhaust subunit;
the air inlet subunit comprises a three-way electromagnetic valve, a particle filter and a nitrogen dioxide adsorber; two inlets of the three-way electromagnetic valve are respectively connected with a background gas inlet pipe and a sample gas inlet pipe, and the background gas inlet pipe is connected with the nitrogen dioxide absorber; an outlet of the three-way electromagnetic valve is connected with an inlet of the particle filter through a pipeline, and an outlet of the particle filter is connected with an air inlet of the optical resonance unit;
the exhaust subunit comprises a barometer, a mass flow meter and a vacuum pump which are sequentially connected through a pipeline, and is connected with an air outlet of the optical resonance unit.
4. The nitrogen dioxide measuring device according to claim 2, wherein the optical resonance unit comprises a cavity, a gas chamber is arranged in the cavity, the side walls of the two ends of the gas chamber are respectively provided with a gas inlet and a gas outlet, the front end of the gas chamber is provided with a front high-reflectivity lens, and the rear end of the gas chamber is provided with a rear high-reflectivity lens;
the air chamber is characterized in that a front collimating lens is arranged at one end of the cavity, a rear collimating lens is arranged at the rear end of the cavity, a broadband optical filter is arranged between the rear collimating lens and the rear high-reflectivity lens, and the front collimating lens, the front high-reflectivity lens, the air chamber, the rear high-reflectivity lens, the broadband optical filter and the rear collimating lens are coaxially arranged.
5. The nitrogen dioxide measurement device of claim 4, wherein the length of the gas chamber is determined by the radius of curvature of the front or rear high reflectance lens.
6. The nitrogen dioxide measuring device of claim 1, wherein the first temperature control unit comprises a box body, a heating layer and a thermocouple are arranged on the inner wall of the box body, and the heating layer and the thermocouple are electrically connected with a temperature controller;
the temperature controller is electrically connected with the control module.
7. The nitrogen dioxide measurement device of claim 6, wherein a heat dissipation fan is further disposed on the wall surface of the box body, and the heat dissipation fan is electrically connected to the temperature controller.
8. The nitrogen dioxide measurement device of claim 1, wherein the second temperature control unit comprises a substrate, a temperature sensor, a semiconductor chilling plate;
the light source of the measuring module is arranged on the substrate, the substrate is provided with a mounting groove, and the temperature sensor is connected with the substrate through the mounting groove and used for detecting the temperature of the substrate;
the back surface of the substrate is tightly attached to the cold surface of the semiconductor refrigerating sheet;
the temperature sensor and the semiconductor refrigeration piece are electrically connected with the control module.
9. The nitrogen dioxide measurement device of claim 8, wherein the hot side of the semiconductor chilling plate is provided with a heat sink; the base plate, the temperature sensor, the semiconductor refrigeration piece and the radiating fin are coated with heat-conducting silicone grease at the contact part of the base plate, the temperature sensor, the semiconductor refrigeration piece and the radiating fin.
10. A nitrogen dioxide measuring method applied to the nitrogen dioxide measuring apparatus according to any one of claims 1 to 9, characterized in that the nitrogen dioxide measuring method comprises the steps of:
monitoring the peripheral temperature of the measuring module and the temperature of the light source by using a temperature control module;
obtaining background gas, removing nitrogen dioxide in the background gas and measuring a spectrum signal of the background gas after the nitrogen dioxide is removed;
acquiring a sample gas and measuring a spectral signal of the sample gas;
determining a nitrogen dioxide absorption coefficient according to the spectral signal of the background gas and the spectral signal of the sample gas;
and determining the nitrogen dioxide concentration of the sample gas according to the nitrogen dioxide absorption coefficient.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112857961A (en) * | 2021-02-01 | 2021-05-28 | 北京大学 | Classification measurement method and system for atmospheric organic nitrate |
| CN115575566A (en) * | 2022-08-04 | 2023-01-06 | 华北电力大学 | Nitrogen oxide measuring system and mass flow controller |
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2020
- 2020-06-15 CN CN202010546228.6A patent/CN111562228A/en active Pending
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112857961A (en) * | 2021-02-01 | 2021-05-28 | 北京大学 | Classification measurement method and system for atmospheric organic nitrate |
| CN115575566A (en) * | 2022-08-04 | 2023-01-06 | 华北电力大学 | Nitrogen oxide measuring system and mass flow controller |
| CN115575566B (en) * | 2022-08-04 | 2023-10-27 | 华北电力大学 | Nitrogen oxide measuring system |
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