NO3 free radical measurement system and method based on zero point measurement

Abstract

The invention relates to the technical field of atmospheric quality measurement, and provides an NO3 free radical measurement system and method based on zero point measurement, and the system comprises a measurement module, a three-way joint, a first air pump, a second air pump and a zero point module; wherein a first joint of the three-way joint is connected with an air inlet of the measuring module, a second joint of the three-way joint is connected with an air outlet of the zero point module, and a third joint of the three-way joint is communicated with the atmosphere; an air outlet of the measuring module is connected with the first air pump; an air inlet of the zero-point module is connected with a second air pump; and the zero point module comprises a spiral steel pipe with a rough inner surface and is used for causing loss of NO3 free radicals in passing gas. According to the invention, zero point measurement is carried out by using the zero point module formed based on the spiral steel pipe, and NO3 free radicals are consumed by using the spiral steel pipe with a rough inner surface, so that the interference of other substances such as water vapor on the measurement precision is effectively avoided, and the accuracy and sensitivity of NO3 free radical measurement of the system are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of air quality measurement, and more specifically, to a NO3 free radical measurement system and method based on zero-point measurement. Background Art

[0002] NO3 free radicals are the most important oxidants driving nighttime atmospheric chemical reactions. They are of great significance for understanding key issues in tropospheric atmospheric chemistry, such as nighttime atmospheric oxidizability, secondary organic aerosol formation, active halogen chemistry, and the global sulfur cycle. Accurate measurement of NO3 free radicals is the basis for conducting nighttime atmospheric chemistry research. NO3 free radicals have high reactivity, short atmospheric lifetime, and low concentration levels, which requires field measurement instruments to have high time resolution, low loss sampling, and high sensitivity. These requirements make accurate field measurements very difficult.

[0003] At present, the mainstream methods of NO3 measurement include cavity enhanced absorption spectroscopy and cavity ring-down absorption spectroscopy, which use the strong absorption characteristics of NO3 at 662nm, and the absorption peak in this band is 10 higher than that of NO2. 3 times. However, when measuring NO3, water vapor has strong absorption in the 660nm band. The absorption of water vapor is narrow-band absorption, and the absorption spectrum is affected by its own concentration, ambient temperature and pressure at the same time. The absorption cross section is different under different temperature, pressure and self-concentration conditions. In the traditional spectrum interpretation process, it is generally through the use of water vapor absorption cross section lookup table under different temperature, pressure and self-concentration conditions, or by iterating the water vapor absorption cross section until the fitting residual is optimized, but these methods are time-consuming and require a lot of computing space. In order to avoid the direct calculation of water vapor concentration, the chemical zero point method is used on the market, such as continuously releasing a small flow of high-concentration NO gas, NO reacts with NO3 in the sample gas, thereby removing NO3 in the sample before reaching the sample detection chamber, and the concentration of water vapor in the sample remains unchanged. At this time, the measured spectrum is the reference spectrum. However, when measuring in the field, it is necessary to carry zero-point gas generation equipment such as NO cylinders with the instrument, which greatly limits the portability of the instrument and increases the difficulty of instrument operation and maintenance. Summary of the invention

[0004] In order to overcome the defect that the external field measurement of NO3 free radical concentration described in the above-mentioned prior art has certain limitations, the present invention provides a NO3 free radical measurement system and method based on zero-point measurement.

[0005] In order to solve the above technical problems, the technical solution of the present invention is as follows:

[0006] A NO3 free radical measurement system based on zero point measurement, comprising a measurement module, a three-way joint, a first air pump, a second air pump and a zero point module; wherein the first joint of the three-way joint is connected to the air inlet of the measurement module, the second joint of the three-way joint is connected to the air outlet of the zero point module, and the third joint of the three-way joint is connected to the atmosphere;

[0007] The air outlet of the measuring module is connected to the air inlet of the first air pump;

[0008] The air inlet of the zero point module is connected to the exhaust port of the second air pump, and the air inlet of the second air pump is connected to the atmosphere;

[0009] The zero point module includes a spiral steel pipe with a rough inner surface, which is used to cause loss of NO3 free radicals in the passing gas;

[0010] When performing zero-point measurement, the first air pump and the second air pump are started, and the measurement module collects and obtains the zero-point signal; when performing gas sampling measurement, the second air pump stops working, and the measurement module collects and obtains the sampling signal; the cyclic sampling is repeated until the preset cyclic sampling period is reached, and the measurement module obtains the NO3 free radical concentration measurement result based on the collected zero-point signal and sampling signal through spectral analysis or signal processing.

[0011] Furthermore, the present invention also proposes a NO3 free radical measurement method based on zero-point measurement, which is applied to the NO3 free radical measurement system based on zero-point measurement proposed in the present invention. The method comprises the following steps:

[0012] S1, starting the first air pump;

[0013] S2, starting the second air pump, and acquiring a zero-point signal through the measurement module until a preset sampling time is reached;

[0014] S3, controlling the second air pump to stop working, and acquiring a sampling signal through the measurement module until a preset sampling time is reached;

[0015] S4, cyclically executing steps S2 to S3 until a preset cyclic sampling period is reached, and the measurement module combines the currently collected zero-point signal and sampling signal to perform spectral analysis or signal processing to obtain a measurement result of NO3 free radical concentration.

[0016] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0017] The present invention uses a zero point module based on a spiral steel pipe to perform zero point measurement, and uses a spiral steel pipe with a rough inner surface to consume NO3 free radicals. The rough inner surface and its spiral structure can increase the contact area and contact time, ensuring that NO3 free radicals in the gas can be consumed when performing zero point measurement, and can effectively avoid the interference of other substances such as water vapor on the measurement accuracy, thereby improving the accuracy and sensitivity of the system NO3 free radical measurement.

[0018] The present invention has the characteristics of portability, easy operation, easy installation, and no maintenance, and can be used in conjunction with other mobile devices to achieve real-time continuous mobile measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 FIG. 4 is an architecture diagram of a NO3 free radical measurement system based on zero-point measurement according to an embodiment of the present invention.

[0020] Figure 2 This is a diagram showing the experimental effect of the loss of NO3 free radicals in a spiral steel pipe according to one embodiment of the present invention.

[0021] Figure 3 FIG. 4 is a schematic diagram of a NO3 free radical measurement system according to an embodiment of the present invention.

[0022] Figure 4 FIG. 4 is a schematic diagram of a NO3 free radical measurement system according to another embodiment of the present invention.

[0023] Figure 5 The figure is a flow chart of a method for measuring NO3 free radicals based on zero-point measurement according to an embodiment of the present invention. DETAILED DESCRIPTION

[0024] Exemplary embodiments will be described in detail herein, examples of which are shown in the accompanying drawings. When the following description refers to the drawings, the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Instead, they are merely examples of devices and methods consistent with some aspects of the present invention as detailed in the appended claims.

[0025] The terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The singular forms "a", "the" and "the" used in the present invention and the appended claims are also intended to include plural forms unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more associated listed items.

[0026] It should be understood that although the terms first, second, third, etc. may be used in the present invention to describe various information, these information should not be limited to these terms. These terms are only used to distinguish the same type of information from each other. For example, without departing from the scope of the present invention, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information. Depending on the context, the word "if" as used herein may be interpreted as "at the time of" or "when" or "in response to determining".

[0027] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] Example 1

[0029] This embodiment proposes a NO3 free radical measurement system based on zero point measurement, such as Figure 1 , which is a structural diagram of the NO3 free radical measurement system based on zero-point measurement in this embodiment.

[0030] The NO3 free radical measurement system based on zero-point measurement proposed in this embodiment includes a measurement module, a three-way joint, a first air pump, a second air pump and a zero-point module; wherein the first joint of the three-way joint is connected to the air inlet of the measurement module, the second joint of the three-way joint is connected to the air outlet of the zero-point module, and the third joint of the three-way joint is connected to the atmosphere.

[0031] Among them, the air outlet of the measurement module is connected to the air inlet of the first air pump; the air inlet of the zero point module is connected to the exhaust port of the second air pump, the air inlet of the second air pump is connected to the atmosphere, and the zero point module includes a spiral steel pipe with a rough inner surface, which is used to cause loss of NO3 free radicals in the passing gas.

[0032] When performing zero-point measurement, the first air pump and the second air pump are started, and the measurement module collects and obtains the zero-point signal; when performing gas sampling measurement, the second air pump stops working, and the measurement module collects and obtains the sampling signal; the cyclic sampling is repeated until the preset cyclic sampling period is reached, and the measurement module obtains the NO3 free radical concentration measurement result based on the collected zero-point signal and sampling signal through spectral analysis or signal processing.

[0033] In this embodiment, taking into account the characteristics of high activity and short life of NO3 free radicals, a spiral steel pipe with a rough inner surface is used to consume NO3 free radicals. The rough inner surface and its spiral structure can increase the contact area and contact time, ensuring that the NO3 free radicals in the gas can be consumed during zero point measurement without affecting the water vapor concentration in the gas.

[0034] For example, this embodiment tests the spiral steel pipe for NO3 free radical loss under laboratory conditions, such as Figure 2 The figure shows the experimental effect diagram of the loss effect of NO3 free radicals in the spiral steel pipe. Among them, the first stage is the high-purity nitrogen spectrum collected in the laboratory, the second stage is the measurement spectrum when the standard source that can produce NO3 free radicals passes through the spiral steel pipe, and the third stage is the measurement spectrum of the standard source directly collected. In order to ensure the accuracy of the experimental results, the average spectrum of all high-purity nitrogen spectra measured in the first stage is used as the zero-point spectrum, and the NO3 free radical concentration in each stage is inverted, and then the average value of the NO3 free radical concentration in each stage is calculated. It can be seen that the spiral steel pipe has a very large loss of NO3 free radicals, and the removal efficiency of the spiral steel pipe for NO3 free radicals is calculated to be 98.76%.

[0035] It should be noted that the removal efficiency of NO3 free radicals is related to the length of the spiral steel pipe. The optimal length of the spiral steel pipe can be calculated based on the residence time of NO3 free radicals on the spiral steel pipe obtained from the test, and the length can be designed according to the requirements of the field measurement environment, which is not limited in this embodiment.

[0036] In addition, since both the physical zero-point device and the detection device adopt passive sampling, it can be considered that when the water vapor concentration and the concentration of other substances remain unchanged during the cycle, as long as the physical zero-point injection port and the sampling port are kept in the same environment, it can be determined that the water vapor concentration and the concentration of other substances remain basically unchanged. The zero-point spectrum obtained in this way has a high accuracy rate.

[0037] The cyclic sampling period set in this embodiment is set according to different regions. The setting standard is based on the change in water vapor concentration. It is generally believed that the water vapor concentration is constant within five minutes.

[0038] Exemplarily, the cyclic sampling period in this embodiment is set to 5 minutes, and it can be considered that the concentration of water vapor and other substances remains substantially unchanged within one sampling period.

[0039] The air inlet of the zero-point module in this embodiment and the third joint of the three-way joint are in the same atmospheric environment to ensure that the concentration of water vapor and other substances remain consistent.

[0040] In this embodiment, the zero-point measurement is performed using a zero-point module composed of spiral steel pipes, which can effectively avoid the interference of water vapor and other substances on the measurement accuracy, and improve the accuracy and sensitivity of the system's NO3 free radical measurement. At the same time, the system has the characteristics of portability, easy operation, easy installation, and no maintenance. It can be used in conjunction with other mobile devices to achieve real-time continuous mobile measurement.

[0041] In an optional embodiment, the zero point module also includes a time relay; wherein the output contacts of the time relay are connected to the control circuit of the second air pump; a cyclic sampling period is preset on the time relay, and when the preset zero point sampling period is reached, the output contacts of the time relay are closed and the control circuit of the second air pump is turned on; when the preset gas sampling period is reached, the output contacts of the time relay are disconnected, and the second air pump stops working.

[0042] For example, Figure 3 FIG. 4 is a schematic diagram of the NO3 free radical measurement system of the present embodiment.

[0043] When the preset zero-point sampling period is reached, the zero-point measurement mode is executed. The output contact of the time relay is connected to the control circuit of the second air pump. When it is triggered, the control circuit of the second air pump is turned on to make the second air pump work. The second air pump draws external gas into the zero-point module to consume the NO3 free radicals in the gas to obtain zero-point gas, and further obtains the zero-point signal through the measurement module.

[0044] When the preset gas sampling cycle is reached, the gas sampling mode is executed, the time relay disconnects the control circuit of the second air pump, the second air pump stops working, and the first air pump continues to work, directly drawing the external gas into the measurement module to obtain a sampling signal.

[0045] The time relay repeatedly works in a cycle until the preset cycle sampling period is reached, and the measurement module obtains the NO3 free radical concentration measurement result through spectral analysis or signal processing based on the collected zero-point signal and sampling signal. It can be considered that the concentration of water vapor and other substances remains basically unchanged within a sampling period, which can avoid the direct calculation of water vapor concentration and the interference of other substance concentrations.

[0046] In an optional embodiment, the system further includes a first flow meter, a second flow meter and a controller; wherein the first flow meter is arranged between the air outlet of the measuring module and the air inlet of the first air pump; and the second flow meter is arranged between the second air pump and the air inlet of the zero point module. The output ends of the first flow meter and the second flow meter are respectively connected to the first input end of the controller, and the first output end of the controller is connected to the control end of the first air pump and / or the second air pump, so as to control the flow rate of the first air pump and / or the second air pump so that the flow rates of the first air pump and the second air pump are equal.

[0047] The flowmeter in this embodiment is used to measure the gas flow rate at the air inlet of the zero point module and the gas flow rate at the air outlet of the measuring module, and cooperates with the controller to control the flow rate of the first air pump and / or the second air pump to achieve the flow rate of the first air pump being equal to the flow rate of the second air pump, further ensuring that the gas filled in the measuring module in the zero point mode is background gas that does not contain NO3 free radicals.

[0048] Further, in an optional embodiment, the zero point module also includes a time relay; wherein the output end of the time relay is connected to the second input end of the controller; the second output end of the controller is connected to the control end of the second air pump; and a cyclic sampling period is preset on the time relay.

[0049] When the preset zero-point sampling period is reached, the time relay outputs a trigger signal to the controller, the controller triggers the zero-point sampling mode and outputs a control signal to the second air pump, and the second air pump works and obtains a zero-point signal through the measurement module;

[0050] When the preset gas sampling period is reached, the time relay stops outputting the trigger signal to the controller, the controller controls the second gas pump to stop working, and the measurement module samples to obtain the sampling signal.

[0051] For example, Figure 4 , which is a schematic diagram of the NO3 free radical measurement system of this embodiment. The connection representations of the first flow meter and the second flow meter with the controller are omitted in the diagram, but it does not mean that there is no connection relationship.

[0052] In this embodiment, the time relay is associated with the controller for control. When the gas sampling is completed and the zero-point measurement mode is jumped to execute, the trigger signal is output to the controller through the time relay, and the controller is further used to control the operation of the second air pump. The second air pump draws external gas into the zero-point module to consume the NO3 free radicals in the gas to obtain zero-point gas, and further obtains the zero-point signal through the measurement module.

[0053] Further, in an optional embodiment, the three-way joint includes a PFA three-way joint.

[0054] In this embodiment, a PFA (polytetrafluoroethylene) three-way connector is used to connect the zero point module and the measurement module. PFA (polytetrafluoroethylene) has low adsorption and excellent chemical inertness, and has little loss of NO3 free radicals, thereby avoiding affecting the measurement results.

[0055] Further, in an optional embodiment, the measurement module includes a detection cavity, a coaxially arranged first convex lens, a second convex lens, a first high-reflection mirror, a second high-reflection mirror, a light source, an optical fiber and a spectrometer.

[0056] Wherein, the first high-reflection mirror and the second high-reflection mirror are coaxially arranged to form an optical resonant cavity;

[0057] The detection cavity is a through-structure at both ends, and is provided with an air inlet and an air outlet; the detection cavity is arranged in the optical resonant cavity;

[0058] The optical signal emitted by the light source passes through the first convex lens, the first high-reflection mirror, the second high-reflection mirror and the second convex lens in sequence, and then passes through the optical fiber into the spectrometer.

[0059] The measurement module in this embodiment performs NO3 free radical measurement based on cavity enhanced absorption spectroscopy technology.

[0060] Exemplarily, the light source is a red LED light source with a central wavelength of 660nm. The first high-reflection mirror and the second high-reflection mirror are a pair of high-reflectivity lenses with a reflectivity higher than 0.9999 in the 640-680nm band, and the first convex lens and the second convex lens are a set of plano-convex lenses.

[0061] During use, the reflectivity of the lens of the NO3 free radical measurement equipment is first calibrated using high-purity nitrogen and helium, two gases with large Rayleigh scattering cross-section differences, according to the formula:

[0062]

[0063] Where λ is the wavelength, and R(λ) is the reflectivity of the high-reflectivity mirror at the calibrated wavelength λ; I He (λ) represents the reference spectra when high-purity nitrogen and helium are input, respectively; n He Respectively represent the concentrations of nitrogen and helium in the sampling chamber; represents the absorption cross section of nitrogen and helium; d is the cavity length of the sampling cavity.

[0064] The degree of lens coupling will affect the effective reflectivity, and the reflectivity will also be reduced due to factors such as particulate matter. Therefore, the reflectivity needs to be calibrated regularly during measurement to obtain a stable reflectivity R(λ) above 0.9999.

[0065] Then, connect the time relay to the power supply, set the sampling cycle, turn on the zero-point mode when the power is turned on, drive the second air pump to work and pump gas into the optical resonant cavity, and set its pumping gas flow rate to be equal to the exhaust gas flow rate of the first air pump to ensure that when the zero-point mode is turned on, all gases in the optical resonant cavity are zero-point gases without NO3 free radicals obtained through the zero-point module, and obtain the zero-point spectrum I0(λ).

[0066] The time relay enters the power-off mode, i.e., the sampling mode. The second gas pump no longer actively pumps gas into the cavity, while the first gas pump maintains the working state. At this time, the gas entering the optical resonant cavity is the sampling gas, and the sampling spectrum I(λ) is obtained.

[0067] Furthermore, the measurement module calculates the absorption coefficient α according to a preset program and combines the spectrum fitting software to obtain the NO3 concentration. The expression is:

[0068]

[0069] Where, λ is the wavelength, R(λ) is the reflectivity of the high reflective mirror at the calibrated wavelength λ; n i is the concentration of the molecule to be measured, d eff is the effective cavity length of the optical cavity in the measurement module; i (λ) is the absorption cross section of NO3 molecules at wavelength λ, α Mie (λ) and α Rayl (λ) represents the light intensity loss caused by Mie scattering and Rayleigh scattering at wavelength λ, respectively.

[0070] By repeating the above zero point mode and sampling mode, the measurement module can continuously calculate the concentration of NO3 free radicals, solve the problem of interference from the concentration of other substances such as water vapor in the measurement of NO3 free radicals, improve the accuracy and sensitivity of measuring atmospheric NO3 free radicals, and avoid data processing for calculating water vapor concentration. At the same time, the device is simple and there is no need to carry NO cylinders, which greatly improves portability.

[0071] Furthermore, in an optional embodiment, the air inlet of the measuring module is connected to a particle filtering device for removing particles in the incoming gas to protect the two highly reflective lenses.

[0072] Example 2

[0073] This embodiment proposes a NO3 free radical measurement method based on zero point measurement, which is applied to the NO3 free radical measurement system based on zero point measurement proposed in Example 1. Figure 5 FIG. 4 is a flow chart of the NO3 free radical measurement method based on zero-point measurement of this embodiment.

[0074] The NO3 free radical measurement method based on zero-point measurement proposed in this embodiment includes the following steps:

[0075] S1, starting the first air pump;

[0076] S2, starting the second air pump, and acquiring a zero-point signal through the measurement module until a preset sampling time is reached;

[0077] S3, controlling the second air pump to stop working, and acquiring a sampling signal through the measurement module until a preset sampling time is reached;

[0078] S4, cyclically executing steps S2 to S3 until a preset cyclic sampling period is reached, and the measurement module combines the currently collected zero-point signal and sampling signal to perform spectral analysis or signal processing to obtain a measurement result of NO3 free radical concentration.

[0079] In an optional embodiment, when the method described in this embodiment is applied to a zero point module composed of a spiral steel pipe, a second air pump and a time relay, the method comprises the following steps:

[0080] S211, the time relay outputs a trigger signal to the control circuit of the second air pump, the control circuit of the second air pump is turned on, and the second air pump works;

[0081] S212, collecting and obtaining a zero-point signal through the measurement module until a preset sampling time has passed;

[0082] S311, the output contact of the time relay is disconnected, the control circuit of the second air pump is disconnected, and the second air pump stops working;

[0083] S312: acquiring a sampling signal through the measurement module until a preset sampling time has passed.

[0084] Among them, the output contact of the time relay in this embodiment is connected to the control circuit of the second air pump; the time relay is preset with a cycle period.

[0085] In another optional embodiment, when the method described in this embodiment is applied to a zero point module consisting of a spiral steel pipe, a second air pump, a time relay and a controller, the method comprises the following steps:

[0086] S221, the time relay outputs a trigger signal to the controller, the controller executes a zero sampling mode and outputs a control signal to the second air pump, and the second air pump works;

[0087] S222, collecting and obtaining a zero-point signal through the measurement module until a preset sampling time has passed;

[0088] S321, the time relay stops outputting the trigger signal to the controller, the controller executes the sampling mode, and controls the second air pump to stop working;

[0089] S322: acquiring a sampling signal through the measurement module until a preset sampling time has passed.

[0090] Among them, the output end of the time relay is connected to the second input end of the controller; the second output end of the controller is connected to the control end of the second air pump; and the time relay is preset with a cycle period.

[0091] It can be understood that the method of this embodiment is applied to the system of the above-mentioned embodiment 1, and the optional items in the above-mentioned embodiment 1 are also applicable to this embodiment, so they are not described repeatedly here.

[0092] Each embodiment of the present invention is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the device embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment. The device embodiment described above is merely exemplary, in which the modules described as separate components may or may not be physically separated, and the functions of each module can be implemented in the same or one or more software and / or hardware when implementing the scheme of the present invention. It is also possible to select some or all of the modules according to actual needs to achieve the purpose of the scheme of this embodiment.

[0093] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A NO3 free radical measurement system based on zero point measurement, characterized in that: It includes a measuring module, a three-way joint, a first air pump, a second air pump and a zero point module; wherein the first joint of the three-way joint is connected to the air inlet of the measuring module, the second joint of the three-way joint is connected to the air outlet of the zero point module, and the third joint of the three-way joint is connected to the atmosphere; The air outlet of the measuring module is connected to the air inlet of the first air pump; The air inlet of the zero point module is connected to the exhaust port of the second air pump, and the air inlet of the second air pump is connected to the atmosphere; The zero point module includes a spiral steel pipe with a rough inner surface, which is used to cause loss of NO3 free radicals in the passing gas; When performing zero-point measurement, the first air pump and the second air pump are started, and the measurement module collects and obtains the zero-point signal; when performing gas sampling measurement, the second air pump stops working, and the measurement module collects and obtains the sampling signal; the cyclic sampling is repeated until the preset cyclic sampling period is reached, and the measurement module obtains the NO3 free radical concentration measurement result based on the collected zero-point signal and sampling signal through spectral analysis or signal processing.

2. The NO3 free radical measurement system based on zero point measurement according to claim 1, characterized in that: The zero point module also includes a time relay; wherein the output contacts of the time relay are connected to the control circuit of the second air pump; a cyclic sampling period is preset on the time relay, and when the preset zero point sampling period is reached, the output contacts of the time relay are closed and the control circuit of the second air pump is turned on; when the preset gas sampling period is reached, the output contacts of the time relay are disconnected, and the second air pump stops working.

3. The NO3 free radical measurement system based on zero point measurement according to claim 1, characterized in that: The system further comprises a first flow meter, a second flow meter and a controller; wherein the first flow meter is arranged between the air outlet of the measuring module and the air inlet of the first air pump; and the second flow meter is arranged between the second air pump and the air inlet of the zero point module; The output ends of the first flow meter and the second flow meter are respectively connected to the first input end of the controller, and the first output end of the controller is connected to the control end of the first air pump and / or the second air pump, so as to control the flow rate of the first air pump and / or the second air pump so that the flow rate of the first air pump and the second air pump are equal.

4. The NO3 free radical measurement system based on zero point measurement according to claim 3, characterized in that: The zero point module further includes a time relay; wherein the output end of the time relay is connected to the second input end of the controller; the second output end of the controller is connected to the control end of the second air pump; The time relay is preset with a cyclic sampling period; When the preset zero-point sampling period is reached, the time relay outputs a trigger signal to the controller, the controller triggers the zero-point sampling mode and outputs a control signal to the second air pump, and the second air pump works and obtains a zero-point signal through the measurement module; When the preset gas sampling period is reached, the time relay stops outputting the trigger signal to the controller, the controller controls the second gas pump to stop working, and the measurement module samples to obtain the sampling signal.

5. The NO3 free radical measurement system based on zero point measurement according to claim 1, characterized in that: The tee connector includes a PFA tee connector.

6. The NO3 free radical measurement system based on zero point measurement according to any one of claims 1 to 5, characterized in that: The measuring module comprises a detection cavity, a first convex lens, a second convex lens, a first high-reflection mirror, a second high-reflection mirror, a light source, an optical fiber and a spectrometer which are coaxially arranged; Wherein, the first high-reflection mirror and the second high-reflection mirror are coaxially arranged to form an optical resonant cavity; The detection cavity is a through-structure at both ends, and is provided with an air inlet and an air outlet; the detection cavity is arranged in the optical resonant cavity; The optical signal emitted by the light source passes through the first convex lens, the first high-reflection mirror, the second high-reflection mirror and the second convex lens in sequence, and then passes through the optical fiber into the spectrometer.

7. The NO3 free radical measurement system based on zero point measurement according to claim 6, characterized in that: The air inlet of the measuring module is connected with a particle filtering device.

8. A method for measuring NO3 free radicals based on zero-point measurement, applied to the NO3 free radical measurement system according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1, starting the first air pump; S2, starting the second air pump, and acquiring a zero-point signal through the measurement module until a preset sampling time is reached; S3, controlling the second air pump to stop working, and acquiring a sampling signal through the measurement module until a preset sampling time is reached; S4, cyclically executing steps S2 to S3 until a preset cyclic sampling period is reached, and the measurement module combines the currently collected zero-point signal and sampling signal to perform spectral analysis or signal processing to obtain a measurement result of NO3 free radical concentration.

9. The NO3 free radical measurement method according to claim 8, characterized in that: The zero point module further includes a time relay; wherein the output contact of the time relay is connected to the control circuit of the second air pump; the time relay is preset with a cycle; then the steps S2 and S3 include: S211, the time relay outputs a trigger signal to the control circuit of the second air pump, the control circuit of the second air pump is turned on, and the second air pump works; S212, collecting and obtaining a zero-point signal through the measurement module until a preset sampling time has passed; S311, the output contact of the time relay is disconnected, the control circuit of the second air pump is disconnected, and the second air pump stops working; S312: acquiring a sampling signal through the measurement module until a preset sampling time has passed.

10. The NO3 free radical measurement method according to claim 8, characterized in that: The zero point module further includes a time relay and a controller; wherein the output end of the time relay is connected to the second input end of the controller; the second output end of the controller is connected to the control end of the second air pump; the time relay is preset with a cycle; then the steps S2 and S3 include: S221, the time relay outputs a trigger signal to the controller, the controller executes the zero sampling mode and outputs a control signal to the second air pump, and the second air pump works; S222, collecting and obtaining a zero-point signal through the measurement module until a preset sampling time has passed; S321, the time relay stops outputting the trigger signal to the controller, the controller executes the sampling mode, and controls the second air pump to stop working; S322: acquiring a sampling signal through the measurement module until a preset sampling time has passed.

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