CN114166920B - Method and system for measuring gaseous nitrous acid concentration in ambient atmosphere - Google Patents

Abstract

The invention provides a method for measuring the concentration of gaseous nitrous acid in ambient atmosphere. The method has the advantages that through the chemical ionization mass spectrometer technology taking iodide ions as reagent ions, direct sampling is performed quickly, the response time is quick, the change of gaseous nitrous acid in a short time can be effectively and accurately observed, and a foundation is provided for better analysis of atmospheric oxidability and pollution causes; the detection method can be used for measuring low-concentration gaseous nitrous acid, the detection limit is tens ppt level, and high sensitivity is ensured; the detection process does not need to rely on absorption solution, is simple to operate and safe to use, has high detection speed, high detection sensitivity and small detection interference, and provides a basis for better analysis of atmospheric oxidability and pollution causes.

Description

Method and system for measuring gaseous nitrous acid concentration in ambient atmosphere

technical field

The invention relates to the field of analysis and detection, in particular to a method and system for measuring the concentration of gaseous nitrous acid in ambient atmosphere.

Background technique

Gaseous nitrous acid (HONO) is an important source of the classic oxidant hydroxyl radical (OH·) in the atmospheric environment, which can directly affect the oxidation capacity of the atmosphere and further control the formation of secondary pollutants such as haze, ozone, etc. and important substances in the study of the causes of air pollution. In the atmosphere, although the concentration of gaseous nitrous acid (HONO) is usually very low, between 0.1-10 ppb, it has very high chemical activity. During the daytime, the atmospheric lifetime of HONO is only 30 minutes to 2 hours, and HONO can rapidly photolyze and generate OH radicals and nitric oxide (NO) under light conditions. And this photolysis is especially important in polluted areas. Recent scientific research shows that the photolysis of HONO can contribute up to 80% to OH radicals in polluted areas. OH free radical is an important classical oxidant in the atmosphere, and is the core substance in atmospheric chemistry and air quality research. It can oxidize volatile organic compounds (VOCs), carbon monoxide (CO), nitrogen oxides (NO _x ), sulfur dioxide ( SO ₂ ), etc., and then affect the production of various pollutants, including secondary aerosols, ozone (O ₃ ) and carbon dioxide (CO ₂ ). However, due to the strong activity, low concentration and short life of OH free radicals, it is very difficult to directly measure them. Therefore, the precursors of OH free radicals (mainly HONO, O ₃ and aldehyde compounds) are measured. It is an important means to analyze the concentration of OH free radicals, carry out the study of atmospheric oxidation and the analysis of the causes of air pollutants.

At present, the sources of gaseous nitrous acid are complicated. Known sources include direct emissions from motor vehicles, heterogeneous transformation of nitrogen dioxide (NO ₂ ), soil release, and nitrate photolysis. The sources are complex and difficult to analyze one by one. However, some recent studies have also shown that there are unknown sources of HONO found in the daytime, and the mechanism of HONO formation in the atmosphere has not been clearly understood. Therefore, instruments and methods that can quickly and accurately measure HONO are needed to further explore The origin, chemical mechanism and impact of HONO in the atmosphere.

At present, there are many methods to measure the concentration of atmospheric HONO, mainly including spectroscopic and wet chemical methods. Among them, spectrometry is a classic method for measuring the concentration of HONO, but the detection limit of the spectrometer is generally high, generally around hundreds of ppt, and the stability of the instrument is poor in field experiments, which is not conducive to the detection of low atmospheric HONO concentration analysis, so spectrometers are generally suitable for laboratory research. The wet chemical method is characterized by a low detection limit, and one of the most commercially successful instruments is the long optical path absorption spectrum (LOPAP) of QUMA Company in Germany, which is based on dual-channel sampling and long optical path absorption colorimetric determination , which can effectively eliminate interference and achieve a lower detection limit (about 10ppt). However, since HONO needs to go through a long liquid channel to be measured after being absorbed by the absorption liquid, the response time of the instrument is long (several minutes). Usually, the time resolution used for atmospheric measurement is ten minutes, and the measurement time is long. In addition, LOPAP instruments are expensive, cumbersome to maintain, and prone to failure due to liquid leakage, which affects the safety and widespread use of equipment.

Contents of the invention

The purpose of the present invention is to provide a method and system for measuring the concentration of gaseous nitrous acid in the ambient atmosphere, aiming at solving the problem of slow response speed, poor sensitivity and poor operation of the measurement method for low-concentration gaseous nitrous acid in the ambient atmosphere in the prior art. complicated question.

For realizing above-mentioned purpose of the invention, the technical scheme that the present invention adopts is as follows:

In a first aspect, the application provides a method for measuring the concentration of gaseous nitrous acid in the ambient atmosphere, comprising the steps of:

Determine the sensitivity and background signal of the instrument: determine the pressure of the vacuum reaction chamber, dilute the HONO standard gas with N groups of zero gas with different relative humidity, and obtain N groups of HONO standard gas with different relative humidity, and N is greater than or equal to 5; respectively detect The sensitivities and background signals of the N groups of HONO gases with different relative humidity, draw the standard curve of the HONO gas sensitivity according to the N groups of different relative humidity and the sensitivity, and obtain the equation of the HONO gas sensitivity, according to the different relative humidity of the N groups Humidity and described background signal draw the standard curve of HONO gas background signal, obtain the equation of HONO gas background signal;

Collecting atmospheric samples: collecting ambient atmospheric samples and measuring the relative humidity of the ambient atmospheric samples, calculating the sensitivity of the ambient atmospheric samples using the equation of the HONO gas sensitivity, and calculating the relative humidity of the ambient atmospheric samples using the equation of the HONO gas background signal background signal;

Calculate the HONO concentration: provide iodide ions to the vacuum reaction chamber, control the flow rate of the ambient air sample into the vacuum reaction chamber through the sampling pipeline, react the ambient air sample with the iodide ion to obtain a reactant, and measure the reaction The mass spectrum signal intensity of IHONO ^- polymerization ion in the thing, the mass spectrum signal intensity and the background signal of I ^- reagent ion, IHCOOH ^- interfering ion; Calculate the concentration of gaseous nitrous acid in the described ambient atmosphere according to the calculation formula of gaseous nitrous acid concentration.

In a second aspect, the present application provides a measurement system for the concentration of gaseous nitrous acid in the ambient atmosphere. The measurement system includes a calibration system, a sampling system, a chemical ionization system, and a quadrupole mass spectrometry system. The calibration system and the chemical The ionization system is connected, the sampling system is connected with the chemical ionization system, and the chemical ionization system is connected with the quadrupole mass spectrometry system;

Among them, the calibration system includes a zero gas generator, an acid scrubber, a HONO generator, a humidity controller, a humidity sensor, a sampling tube and a bypass tube. The zero gas generator is connected to the HONO generator, and the acid scrubber is connected to the HONO generator. , the HONO generator is connected to the sampling tube, the humidity controller is connected in parallel to the HONO generator, one end of the humidity sensor is connected between the HONO generator and the sampling tube, the other end is connected to the bypass tube, the output end of the sampling tube is connected to the chemical ionization The vacuum reaction chamber connection of the system;

The sampling system includes a main intake pipe, a particle separator, a bypass pipe and an instrument intake pipe. The total intake pipe is connected to the bypass pipe and the instrument intake pipe through the particle separator, and the instrument intake pipe is connected to the vacuum reaction chamber of the chemical ionization system;

The chemical ionization system includes an ion source and a vacuum reaction chamber, the ion source is connected to the vacuum reaction chamber, and the vacuum reaction chamber is connected to the collision dissociation chamber of the quadrupole mass spectrometry system;

The quadrupole mass spectrometer system includes a collision dissociation chamber, a quadrupole mass spectrometer filter chamber and an ion detector, the collision dissociation chamber is connected with the quadrupole mass spectrometer filter chamber, and the quadrupole mass spectrometer filter chamber is connected with the ion detector.

In the method for measuring the concentration of gaseous nitrous acid in the ambient atmosphere provided by the first aspect of the application, iodide ions are used as the reaction reagent. Because the reactivity of iodide ions and water is very strong, the humidity in the environment will affect the sensitivity of the reaction, so Before analyzing the sample, the sensitivity of the instrument is calibrated by using the HONO standard gas generated by the HONO generator under the pressure of a certain vacuum reaction chamber, and the sensitivity and background signal of the HONO gas diluted with different relative humidity are calibrated, and N Greater than or equal to 5, ensure that a certain number of samples with different humidity can draw the standard curve of "relative humidity-HONO gas sensitivity" and "relative humidity-HONO gas background signal" for subsequent sampling analysis.

Secondly, the ambient air samples are directly collected for analysis without pretreatment or concentration of the ambient air samples to ensure the detection of low-concentration HONO gas; the ambient air samples to be tested are reacted with iodide ions, and The HONO gas in the sample undergoes an addition reaction to form IHONO ^- polymerized ions, and then the information such as the mass spectrum signal intensity of the IHONO ^- polymerized ions and each impurity ion in the reactant is measured, and the concentration of HONO can be obtained by further calculation.

The above-mentioned test method is quickly measured by direct sampling and using chemical ionization mass spectrometry, and the response time is fast, which can effectively and accurately observe the change of gaseous nitrous acid in a short period of time. This detection method can detect low-concentration gaseous nitrous acid. Determination, the detection limit is tens of ppt level, which guarantees high sensitivity; the detection process is different from the traditional wet chemical method, does not need to rely on the absorption solution, simple operation, safe use, fast detection speed, detection High sensitivity and low detection interference provide a basis for better analysis of atmospheric oxidation and pollution causes.

The second aspect of the present application provides a measurement system for the concentration of gaseous nitrous acid in the ambient atmosphere. The measurement system includes a calibration system, a sampling system, a chemical ionization system, and a quadrupole mass spectrometry system. The concentration of gaseous nitrous acid in the medium is measured, with fast detection speed, high sensitivity, and little interference, and there are no consumables that need to be replaced frequently in the entire measurement system. There is no need to worry about the possible harm to electronic equipment caused by solution leakage in the design. The operation is simple and convenient, and can realize The operation and maintenance workload is small, and it is safe to use, which is conducive to being widely used in HONO measurement of outdoor ambient atmosphere.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present application, the accompanying drawings that need to be used in the descriptions of the embodiments or the prior art will be briefly introduced below. Obviously, the accompanying drawings in the following description are only for the present application For some embodiments, those of ordinary skill in the art can also obtain other drawings based on these drawings without creative effort.

Fig. 1 is a schematic diagram of a measurement system for the concentration of gaseous nitrous acid in the ambient atmosphere provided by an embodiment of the present invention.

Fig. 2 is a schematic diagram of a calibration system provided by an embodiment of the present invention.

Fig. 3 is a schematic diagram of a sampling system provided by an embodiment of the present invention.

Fig. 4 is a schematic diagram of a chemical ionization system provided by an embodiment of the present invention.

Fig. 5 is a schematic diagram of a quadrupole mass spectrometry system provided by an embodiment of the present invention.

Fig. 6 is a standard curve for plotting HONO gas sensitivity with different relative humidity and sensitivity provided by the embodiment of the present invention.

Fig. 7 is a standard curve for plotting HONO gas background signal with different relative humidity and background signal provided by the embodiment of the present invention.

Fig. 8 is a signal diagram of each ion mass spectrum of the ambient air measurement results provided by Embodiment 2 of the present invention.

Fig. 9 is the measurement result of the response time of the HONO gas provided by Example 4 of the present invention.

Fig. 10 is the measurement result of Example 2 (CIMS) provided in Comparative Example 1 of the present invention and the measurement result of HONO gas in Comparative Example 1 (LOPAP instrument).

Detailed ways

In order to make the purpose, technical solutions and technical effects of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than Full examples. In combination with the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

In the description of the present invention, it should be understood that the terms "first" and "second" are used for description purposes only, and cannot be interpreted as indicating or implying relative importance or implicitly indicating the quantity of indicated technical features. Thus, a feature defined as "first" and "second" may explicitly or implicitly include one or more of these features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

Example of the present invention provides a kind of measurement method of gaseous nitrous acid concentration in ambient atmosphere, comprises the steps:

S01. Determine the sensitivity and background signal of the instrument: determine the pressure of the vacuum reaction chamber, dilute the HONO standard gas with N groups of zero gas with different relative humidity, and obtain the HONO standard gas under N groups with different relative humidity, and N is greater than or equal to 5; Detect the sensitivity and background signal of HONO gas with different relative humidity in N groups respectively, draw the standard curve of HONO gas sensitivity according to the different relative humidity and sensitivity of N groups, obtain the equation of HONO gas sensitivity, and draw HONO gas according to the different relative humidity and background signal of N group The standard curve of the gas background signal, the equation for obtaining the HONO gas background signal;

S02. Collect atmospheric samples: collect ambient atmospheric samples and measure the relative humidity of the ambient atmospheric samples, calculate the sensitivity of the ambient atmospheric samples using the equation of HONO gas sensitivity, and obtain the background signal of the ambient atmospheric samples by calculating the equation of the HONO gas background signal;

S03. Calculate the HONO concentration: provide iodide ions to the vacuum reaction chamber, control the flow rate of the ambient air sample into the vacuum reaction chamber through the sampling pipeline, react the ambient air sample with iodide ions to obtain the reactant, and measure the IHONO ^- polymeric ion in the reactant The mass spectrum signal intensity of I ^- reagent ion, IHCOOH ^- interfering ion mass spectrum signal intensity and background signal; according to the calculation formula of gaseous nitrous acid concentration, the concentration of gaseous nitrous acid in the ambient atmosphere is calculated.

The test method for the concentration of gaseous nitrous acid in the ambient atmosphere of the present invention is quickly measured by direct sampling and using the method of chemical ionization mass spectrometry, the response time is fast, and the change of gaseous nitrous acid in a short period of time can be effectively and accurately observed. Provide a basis for better analysis of atmospheric oxidation and pollution causes; this detection method can detect low-concentration gaseous nitrous acid, and the detection limit is tens of ppt levels, ensuring high sensitivity; the detection process is different from traditional The unique wet chemical method does not need to rely on the absorption solution, and is easy to operate and safe to use. This method has fast detection speed, high detection sensitivity, and low detection interference, which provides a basis for better analysis of atmospheric oxidation and pollution causes.

Specifically, in the above step S01, this step is to determine the sensitivity of the instrument and the background signal. Determine the pressure of the vacuum reaction chamber, and dilute the HONO standard gas with N groups of zero gas with different relative humidity to obtain N groups of HONO standard gas at different relative humidity, and N is greater than or equal to 5; respectively detect N groups of HONO with different relative humidity Gas sensitivity and background signal, draw the standard curve of HONO gas sensitivity according to the different relative humidity and sensitivity of N groups, obtain the equation of HONO gas sensitivity, draw the standard curve of HONO gas background signal according to the different relative humidity and background signal of N groups, and obtain HONO The equation of the gas background signal, in the test method of the present invention, adopts iodide ion as reaction reagent, because the reactivity of iodide ion and water is very strong, the humidity in the environment can affect the sensitivity of reaction, so before analyzing the sample, by certain Under the condition of vacuum reaction chamber pressure, analyze the sensitivity and background signal of HONO gas diluted with different relative humidity, and N is greater than or equal to 5, so as to ensure that a certain number of samples with different humidity can draw "relative humidity-HONO gas sensitivity" and The standard curve of "relative humidity-HONO gas background signal" is used for subsequent experimental analysis.

Specifically, since the pressure of the vacuum reaction chamber in the system has a certain influence on the detection sensitivity, the sensitivity will be different under different pressure systems of the vacuum reaction chamber, so the pressure of the vacuum reaction chamber is determined to be tested under certain conditions, and the guarantee The pressure value of the vacuum reaction chamber is consistent with the pressure of the vacuum reaction chamber in the subsequent sampling process, so as to facilitate the subsequent calculation of the sensitivity of the ambient air sample and the background signal of the ambient air sample.

Preferably, in the step of determining the pressure of the vacuum reaction chamber, the pressure of the vacuum reaction chamber is 20-80 torr. In a specific embodiment of the present invention, the control pressure is 62 torr. Further, when the pressure is 62torr, the precursors of other important atmospheric oxidants can be effectively monitored at the same time, including NO ₃ radical precursors N ₂ O ₅ , Cl radical precursors (ClNO ₂ , Cl ₂ and BrCl) and Br radical precursors ( _Br2 and HOBr) and other pollutants, greatly improving the scope of application.

Preferably, the relative humidity is 20%-80%. Under the above humidity conditions, the influence of different relative humidity on the detection of HONO gas can be analyzed. Among them, relative humidity refers to the percentage of the water vapor pressure in the air and the saturated water vapor pressure at the same temperature.

Preferably, under a certain pressure condition, a calibration system is used to analyze the influence of different relative humidity on the detection of HONO gas.

Preferably, as shown in accompanying drawing 2, calibration system comprises zero gas generator (1), acid scrubber (2), HONO generator (3), humidity controller (4), humidity sensor (5), sampling tube (6) and calibration bypass pipe (7). The zero gas generator is connected to the HONO generator, the acid scrubber is connected to the HONO generator, the HONO generator is connected to the sampling pipe, the humidity controller is connected to the HONO generator in parallel, and one end of the humidity sensor is connected between the HONO generator and the sampling pipe , the other end is connected with the bypass pipe, and the output end of the sampling pipe is connected with the vacuum reaction chamber of the chemical ionization system.

In some embodiments, the zero gas generator is selected from the Model 111 produced by Thermo Company, and the generated zero gas needs to pass through an acid gas absorption box containing glass fibers covered with sodium carbonate to further remove trace amounts of HONO gas.

In some embodiments, the HONO generator is produced by QUMA Company of Germany, and the HONO generator includes a spiral tube reactor and cooling circulating water.

In some embodiments, the humidity controller is to adjust the humidity of the zero gas, and further control the influence of different relative humidity on the detection of HONO gas.

In some embodiments, the purpose of the acid scrubber is to provide a mixed solution of dilute sulfuric acid and nitrous acid to produce nitrous acid gas.

In some embodiments, the humidity sensor is used to measure the humidity of the incoming HONO standard gas.

Wherein, the output end of the sampling tube is connected with the vacuum reaction chamber of the chemical ionization system, and the HONO standard gas is passed into the chemical ionization system for analysis.

In some embodiments, during the process of gas calibration using the calibration system, the dilute sulfuric acid (1M) solution and nitrous acid solution in the acid scrubber are pumped into the helical tube reactor of the HONO generator at a fixed flow rate through a peristaltic pump. After mixing, the reaction produces nitrous acid, which is blown out through the 2L/min zero gas provided by the zero gas generator; the humidity controller is used to adjust, and the total flow rate provided by the zero gas generator is 8L/min. The diluted zero gas passes through two channels respectively , one way is humidified through the water bubbler, and the other way is not humidified. The humidity sensor is used to detect the zero air humidity loaded with nitrous acid gas, and it is mixed with the 2L/min nitrous acid gas generated by the HONO generator to obtain a mixed gas, which is passed through the sampling tube. A quadrupole mass spectrometry system was used to analyze the sensitivity of HONO gas at different humidity.

In a preferred embodiment of the present invention, a calibration system is provided to dilute the HONO gas in N groups of different relative humidity environments to obtain N groups of HONO gas with different relative humidity, and detect the sensitivity and background signal of N groups of HONO gas with different relative humidity. Further, a chemical ionization system was used to detect the sensitivity and background signal of HONO gases with different relative humidity.

Specifically, draw the standard curve of HONO gas sensitivity according to the different relative humidity and sensitivity of N groups, obtain the equation of HONO gas sensitivity, draw the standard curve of HONO gas background signal according to the different relative humidity and background signals of N groups, and obtain the equation of HONO gas background signal equation. Wherein, since the water molecules in the air react reversibly with the IHONO ^- ions, as shown in the following reaction formula: Therefore, the sensitivity and background signal of the instrument for the measurement of HONO will decrease with the increase of relative humidity (RH). According to the different relative humidity, sensitivity and background signal of N groups, the standard curve of HONO gas sensitivity is an exponential decay curve. Since the pressure in the reaction process will affect the reaction rate of I ^- and HONO, and the reaction rate of IHONO ^- and H ₂ O, the sensitivity and background signal will decrease with the decrease of the pressure in the reaction process, but the RH impact will slow down.

In the above step S02, this step is to collect atmospheric samples. Collect ambient air samples and measure the relative humidity of the ambient air samples. Preferably, remove the aerosol particles from the collected ambient air samples to reduce the accumulation of aerosol particles in the atmosphere in the sampling pipeline to interfere with the measurement of HONO, ensuring It can detect low-concentration HONO gas. This detection method can measure low-concentration gaseous nitrous acid. The detection limit is tens of ppt level, which ensures high sensitivity and less interference.

Preferably, as shown in FIG. 3 , the sampling system includes a total intake pipe (1), a particle separator (4), a bypass pipe (2) and an instrumental sampling pipe (3). The total intake pipe is connected to the bypass pipe and the instrument intake pipe through the particle separator, and the instrument intake pipe is connected to the chemical ionization system; when the gas enters the system through the inlet, it reaches the particle separator through the total sampling pipe, and the gas in the Aerosol particles are removed, so that the aerosol particles are removed from the bypass port; the gas after removing the aerosol particles is led out to the chemical ionization system through the instrument sampling tube for subsequent analysis.

Preferably, the material of the sampling system is selected from Teflon materials, and a sampling system prepared by Teflon materials is provided to collect ambient air samples, and a particle separator is used to remove aerosol particles of the ambient air samples; the sampling system is used for sampling Acquisition and removal of aerosol particles can reduce the deposition of aerosol particles on the wall of the sampling tube, thereby avoiding pipeline interference caused by heterogeneous reactions in the pipeline.

Preferably, in the step of using the sampling system to collect the ambient air sample, the ambient air sample enters through the air inlet, passes through the particle separator, and uses a flow rate of 12 to 15 lpm to remove the aerosol particles of the ambient air sample from the bypass pipe, The ambient air sample containing HONO was collected from the air sample collection tube with a flow rate of 1.5-2.5 lpm. Under the above conditions, adopting a sampling system including a particle separator and using a large-flow airflow can ensure that the aerosol particles in the atmospheric sample go out from the bypass port, and then use a small-flow airflow to remove the aerosol particles. Ambient air samples containing HONO are collected and tested by instruments to ensure that the samples are free from the interference of heterogeneous reactions of aerosol particles, which is conducive to the detection of low-concentration HONO gas.

Preferably, an external humidity detector is used to measure the relative humidity of the ambient air sample. By measuring the relative humidity of the ambient air sample, the measured relative humidity value is calculated using the equation of HONO gas sensitivity to obtain the sensitivity of the ambient air sample. Using HONO gas The equation of the background signal is calculated to obtain the background signal of the ambient air sample for subsequent experiments.

In the above step S03, this step is to calculate the concentration of HONO. Provide iodide ions to the vacuum reaction chamber; preferably, in the step of providing iodide ions, an α-radiation source is used in the ion source to ionize the mixed gas of methyl iodide and nitrogen to obtain iodide ions, wherein the α-radiation source is selected from ²¹⁰ Any one of Po, ²²⁶ Ra, ²²⁸ Th, ²³⁸ Pu, ²³⁹ Pu, ²⁴¹ Am.

Preferably, as shown in Figure 4, the chemical ionization system includes an ion source and a vacuum reaction chamber. The ion source is connected with the vacuum reaction chamber, and the vacuum reaction chamber is connected with the collision dissociation chamber of the quadrupole mass spectrometry system.

In some embodiments, the chemical ionization system is selected from a chemical ionization mass spectrometer. In some embodiments, the chemical ionization mass spectrometer is selected from those manufactured by THS Instruments LLC in Georgia, USA.

In some embodiments, in the chemical ionization system, the alpha radiation source is used to rapidly ionize iodide ions, and the ambient air sample to be tested is reacted with iodide ions. Since iodide ions have a strong electron affinity, they are compatible with the Addition reaction occurs to HONO gas in the ambient air sample measured, and the reaction formula of the addition reaction is as follows: I- ⁺ HONO+M= ^IHONO- +M, the reaction forms IHONO ^- polyion, and this detection method is due to the rapid release of iodide ion, which is compatible with The sample reacts quickly for determination, and the response time is fast, which can effectively and accurately observe the change of gaseous nitrous acid in a short period of time.

Preferably, methyl iodide (CH ₃ I) is selected for ionization to obtain iodide ions, and an addition reaction occurs with HONO gas in the ambient air sample to be measured to form IHONO ^- polymerized ions, which is beneficial to the determination of the concentration of HONO gas. Iodide ion was used as the reactant ion. In a preferred embodiment of the present invention, methyl iodide/nitrogen cylinder gas is prepared by mixing methyl iodide and nitrogen for use.

Preferably, the flow rate of methyl iodide is 1-10 sccm, and the concentration of methyl iodide is 3000-4000 ppm. Controlling the flow rate and concentration of methyl iodide can ensure the subsequent ionization to obtain an appropriate concentration of iodide ions. If the flow or concentration of methyl iodide is too low, iodide ions cannot be generated quickly during the ionization process using α-radiation sources, which will affect the response time of the detection and result in a longer detection time; if the flow or concentration of methyl iodide is too high , because methyl iodide is in a liquid state at room temperature, it is easy to remain inside the tube wall, which affects the detection sensitivity.

Preferably, nitrogen and methyl iodide are provided for mixing, the purpose of mixing is to adjust the concentration of methyl iodide to make the ionization effect better. Preferably, the flow rate of nitrogen gas is 100-1000 sccm, and the purity of nitrogen gas is ≥99.99%. The flow rate of nitrogen gas is controlled to be large, and mixed with methyl iodide, the concentration of methyl iodide can be further adjusted, which is conducive to subsequent rapid ionization to obtain iodide ions; The purpose of selecting high-purity nitrogen with a purity of 99.99% is to reduce the generation of O ₂ ^- ions, thereby avoiding interference.

Preferably, iodine ions are obtained by ionizing the mixed gas with an α-radiation source. The α-radiation source is made of a nuclide that emits α-particles and is mainly characterized by emitting α-particles. Preferably, the α-radiation source is selected from any one of ²¹⁰ Po, ²²⁶ Ra, ²²⁸ Th, ²³⁸ Pu, ²³⁹ Pu, and ²⁴¹ Am. If any α-radiation source is selected for testing, it can be quickly ionized to obtain iodide ions. In the preferred embodiment of the present invention, ²¹⁰ Po is selected for experimentation.

Further, control the flow rate of the ambient air sample into the vacuum reaction chamber through the sampling pipeline. Since the pressure and flow rate of the vacuum reaction chamber obtained by sampling are relatively large, in the process of reacting with iodide ions in the vacuum reaction formula, if the pressure and flow rate are too large , will cause iodide ions to be neutralized rapidly, it cannot be guaranteed that iodide ions only react with HONO gas, and it cannot be guaranteed that only IHONO ^- polymerized ions are included in the reactant, and other reaction impurities will be formed, which will affect the sensitivity of the assay. In some embodiments, the flow of the ambient air sample through the sampling line into the vacuum reaction chamber is controlled by a restrictor hole.

Preferably, in the step of controlling the flow rate of the ambient air sample into the vacuum reaction chamber through the sampling pipeline, the flow rate of the ambient air sample into the vacuum reaction chamber through the sampling pipeline is 0.5-2.0 slpm, and the pressure and flow rate of the ambient air sample are controlled to be small , to ensure complete reaction with iodide ions, so that only IHONO ^- polymerized ions are generated in the product, which is beneficial to subsequent determination and ensures high sensitivity.

Specifically, the ambient air sample is reacted with iodide ions to obtain a reactant, which undergoes an addition reaction with HONO gas in the ambient air sample. The reaction formula of the addition reaction is as follows: ^I- +HONO+M= ^IHONO- +M, the reaction forms IHONO ^- polymeric ion.

Preferably, in the step of reacting the ambient air sample with iodide ions to obtain reactants, a chemical ionization system is used for the reaction. Further preferably, in the step of reacting the ambient air sample with iodide ions to obtain the reactant, the reaction step is carried out in a vacuum reaction chamber of a chemical ionization system, wherein the material of the vacuum reaction chamber is 304 stainless steel, and the vacuum reaction chamber The shape is cylindrical. In some embodiments, the vacuum reaction chamber of 304 stainless steel material is selected for reaction, because 304 stainless steel material has good corrosion resistance, heat resistance, low temperature strength and mechanical properties, good thermal workability such as stamping and bending, and no heat treatment hardening Therefore, the vacuum reaction chamber made of 304 stainless steel can ensure that the reaction process is free of impurities, and the accuracy of the reaction is improved; at the same time, it also ensures that the reaction chamber is durable and can be used repeatedly. In some other embodiments, the shape of the vacuum reaction chamber is cylindrical, and a cylindrical reaction formula is adopted, which is beneficial to gas circulation, improves response time, reduces the contact between gas and the tube wall, and ensures the reaction rate.

Further preferably, the length of the vacuum reaction chamber is 3-10 cm, and the inner diameter is 4-8 cm. If the volume of the vacuum reaction chamber is too small, the reaction time will be insufficient and the reaction will not be complete; if the volume of the vacuum reaction chamber is too large, it will cause secondary reactions between the gas and iodide ions to form impurities, which will affect the sensitivity of the detection results.

Preferably, in the step of measuring the mass spectrum signal intensity of IHONO ^- polymerization ion in the reactant, the mass spectrum signal intensity of I ^- ion, IHCOOH ^- interfering ion and the background signal, a quadrupole mass spectrometry system is used for determination.

Preferably, as shown in FIG. 5 , the quadrupole mass spectrometer system includes a collision dissociation chamber, a quadrupole mass spectrometer filter chamber and an ion detector. The collision dissociation chamber is connected with the vacuum reaction chamber of the chemical ionization system, the collision dissociation chamber is connected with the quadrupole mass spectrometer filter chamber, and the quadrupole mass spectrometer filter chamber is connected with the ion detector.

In a preferred embodiment of the present invention, the quadrupole mass spectrometer system is selected from quadrupole mass spectrometers. In some embodiments, the quadrupole mass spectrometer is selected from those manufactured by THS Instruments LLC in Georgia, USA.

Preferably, when the IHONO ^- polymeric ion is detected by mass spectrometry, its mass-to-nucleus ratio is 174, and the mass ^- nuclear signal intensity of the IHONO ^- polymerized ion can be detected when the mass-to-nucleus ratio is 174; When the mass-to-nucleus ratio is 127, the mass spectrum signal intensity of the I ^- ion can be detected; when the IHCOOH ^- interfering ion is detected by mass spectrometry, its mass-to-nucleus ratio is 173, and the IHCOOH ^- interference ion can be detected at a mass-to-nucleus ratio of 173 The mass spectrometric signal intensity of the ion.

Specifically, the concentration of gaseous nitrous acid in the ambient atmosphere is calculated according to the formula for calculating the concentration of gaseous nitrous acid. Preferably, according to the sensitivity of the ambient air sample, the background signal of the ambient air sample, the mass spectrum signal intensity of IHONO ^- polymerization ion, the mass spectrum signal intensity and background signal of I ^- reagent ion, the mass spectrum signal intensity and background signal calculation of IHCOOH ^- interfering ion Obtain the concentration of gaseous nitrous acid in the ambient atmosphere.

Wherein, the concentration of gaseous nitrous acid in the ambient atmosphere is directly proportional to the mass spectrum signal intensity of the IHONO ^- polymerized ion in the measured reactant. In order to avoid the influence of impurity ions in the chemical ionization mass spectrometer, the ^IHONO- in the measured reactant The mass spectrum signal intensity of the aggregated ion needs to be standardized and corrected with the reagent ion I ^- ion, and the interference of the ¹³ C isotope signal of the IHCOOH ^- interfering ion on the HONO signal needs to be considered. At the same time, the background signal and sensitivity of the HONO gas in the ambient air sample also need to be considered Calibration curve with relative humidity.

Preferably, the calculation formula of gaseous nitrous acid concentration is:

Among them, SIG _174/127 is the ratio of the mass spectrum signal intensity of IHONO ^- polymerization ion to the mass spectrum signal intensity of I ^- reagent ion; BKG _{ambient air sample} is the background signal of ambient air sample; SIG _173/127 is the mass spectrum of IHCOOH ^- interfering ion The ratio of the signal intensity to the mass spectrum signal intensity of the I ^- reagent ion; BKG _173/127 is the ratio of the background signal of the IHCOOH ^- interfering ion to the background signal of the I ^- reagent ion; SENS _{ambient air sample} is the sensitivity of the ambient air sample; 1.2% (SIG _173/127 -BKG _173/127 ) is the signal intensity of the ¹³ C isotope ratio in formic acid.

The above test method adopts direct sampling and rapid measurement, and has a fast response time, and can effectively and accurately observe the change of gaseous nitrous acid in a short period of time. This detection method can measure low-concentration gaseous nitrous acid, and the detection limit is tens of The ppt level ensures high sensitivity; the detection process is different from the traditional wet chemical method, does not need to rely on the absorption solution, simple operation, safe use, fast detection speed, high detection sensitivity, low detection interference, for Provide a basis for better analysis of atmospheric oxidation and pollution causes.

Correspondingly, an embodiment of the present invention also provides a measurement system for the concentration of gaseous nitrous acid in the ambient atmosphere. The measurement system includes a sequentially connected sampling system, a chemical ionization system, and a quadrupole mass spectrometry system.

The present invention provides a measurement system for the concentration of gaseous nitrous acid in the ambient atmosphere. As shown in Figure 1, the measurement system includes a calibration system, a sampling system, a chemical ionization system and a quadrupole mass spectrometry system. The calibration system is connected with the quadrupole mass spectrometry system, the sampling system is connected with the chemical ionization system, and the chemical ionization system is connected with the quadrupole mass spectrometry system.

The measurement system is used to measure the concentration of gaseous nitrous acid in the ambient atmosphere. The detection speed is fast, the sensitivity is high, and the interference is small. There are no consumables that need to be replaced frequently in the entire measurement system. There is no need to worry about the possible harm to electronic equipment caused by solution leakage in the design. The operation is simple and convenient, the operation and maintenance workload can be reduced, the use is safe, and it is beneficial to be widely used in the gas detection of the outdoor environment atmosphere.

Specifically, the calibration system included in the measurement system for the concentration of gaseous nitrous acid in the ambient atmosphere can analyze the influence of different relative humidity on the detection of HONO gas, and further determine the sensitivity of the detection of HONO gas.

Specifically, as shown in Figure 2, the calibration system includes a zero gas generator (1), an acid scrubber (2), a HONO generator (3), a humidity controller (4), a humidity sensor (5), a sampling tube (6) and bypass pipe (7). The zero gas generator is connected to the HONO generator, the acid scrubber is connected to the HONO generator, the HONO generator is connected to the sampling pipe, the humidity controller is connected to the HONO generator in parallel, and one end of the humidity sensor is connected between the HONO generator and the sampling pipe , the other end is connected with the bypass pipe, and the output end of the sampling pipe is connected with the vacuum reaction chamber of the chemical ionization system.

In some embodiments, the zero gas generator is selected from the Model 111 produced by Thermo Company, and the generated zero gas needs to pass through an acid gas absorption box containing glass fibers covered with sodium carbonate to further remove trace amounts of HONO gas.

In some embodiments, the HONO generator is produced by QUMA Company of Germany, and the HONO generator includes a spiral tube reactor and cooling circulating water.

In some embodiments, the zero gas generator is to adjust the humidity of the zero gas to further control the influence of different relative humidity on the detection of HONO gas.

In some embodiments, the purpose of the acid scrubber is to provide a mixed solution of dilute sulfuric acid and nitrous acid to produce nitrous acid gas.

In some embodiments, the humidity sensor is used to control the humidity of the nitrous acid gas introduced;

Further, the output end of the sampling tube is connected to the chemical ionization system, and the HONO standard gas is directly passed into the chemical ionization system for calibration.

In some embodiments, during the process of gas calibration using the calibration system, the dilute sulfuric acid (1M) solution and nitrous acid solution in the acid scrubber are pumped into the helical tube reactor of the HONO generator at a fixed flow rate through a peristaltic pump. After mixing, the reaction produces nitrous acid, which is blown out through the 2L/min zero gas provided by the zero gas generator; the humidity controller is used to adjust, and the total flow rate provided by the zero gas generator is 8L/min. The diluted zero gas passes through two channels respectively , one way is humidified through the water bubbler, and the other way is not humidified. Use the humidity sensor to detect the humidity of nitrous acid gas, mix it with the 2L/min nitrous acid gas generated by the HONO generator to obtain a mixed gas, and then pass it into the chemical ionization through the sampling tube The system analyzes the sensitivity of HONO gas under different humidity.

In a preferred embodiment of the present invention, a calibration system is provided to dilute the HONO gas in N groups of different relative humidity environments to obtain N groups of HONO gas with different relative humidity, and detect the sensitivity and background signal of N groups of HONO gas with different relative humidity. Further, a chemical ionization system was used to detect the sensitivity and background signal of HONO gases with different relative humidity.

Specifically, as shown in Figure 3, the sampling system includes a total intake pipe (1), a particle separator (4), a bypass pipe (2), and an instrument sampling pipe (3). The pipeline and the instrument sampling tube are connected, and the instrument sampling tube is connected to the chemical ionization system; when the gas enters the system from the main air inlet, it passes through the main air inlet to the particle separation, removes the aerosol particles in the gas, and makes the aerosol Particles are removed by the bypass port; the gas after removing the aerosol particles is led out to the chemical ionization system through the instrument sampling tube for subsequent analysis.

Preferably, in the sampling system, the materials of the total intake pipe, the bypass pipe and the instrument intake pipe are selected from Teflon materials. The system is prepared with Teflon material, which is beneficial to sample collection and reduces pipeline interference.

Specifically, as shown in Figure 4, the chemical ionization system ion source and vacuum reaction chamber. The ion source is connected with the vacuum reaction chamber, and the vacuum reaction chamber is connected with the collision dissociation chamber of the quadrupole mass spectrometry system.

In some embodiments, the chemical ionization system is selected from a chemical ionization mass spectrometer. In some embodiments, the chemical ionization mass spectrometer is selected from those manufactured by THS Instruments LLC in Georgia, USA.

In some embodiments, in the chemical ionization system, the alpha radiation source is used to rapidly ionize iodide ions, and the ambient air sample to be tested is reacted with iodide ions. Since iodide ions have a strong electron affinity, they are compatible with the Addition reaction occurs to HONO gas in the ambient air sample measured, and the reaction formula of the addition reaction is as follows: I- ⁺ HONO+M= ^IHONO- +M, the reaction forms IHONO ^- polyion, and this detection method is due to the rapid release of iodide ion, which is compatible with The sample reacts quickly for determination, and the response time is fast, which can effectively and accurately observe the change of gaseous nitrous acid in a short period of time.

Preferably, the chemical ionization system includes a vacuum reaction chamber, wherein the material of the vacuum reaction chamber is 304 stainless steel, and the shape of the vacuum reaction chamber is cylindrical. In some embodiments, the vacuum reaction chamber of 304 stainless steel material is selected for reaction, because 304 stainless steel material has good corrosion resistance, heat resistance, low temperature strength and mechanical properties, good thermal workability such as stamping and bending, and no heat treatment hardening Therefore, the vacuum reaction chamber made of 304 stainless steel can ensure that the reaction process is free of impurities, and the accuracy of the reaction is improved; at the same time, it also ensures that the reaction chamber is durable and can be used repeatedly. In some other embodiments, the shape of the vacuum reaction chamber is cylindrical, and a cylindrical reaction formula is adopted, which is beneficial to gas circulation, improves response time, reduces the contact between gas and the tube wall, and ensures the reaction rate.

Further preferably, the length of the vacuum reaction chamber is 3-10 cm, and the inner diameter is 4-8 cm. If the volume of the vacuum reaction chamber is too small, the reaction time will be insufficient and the reaction will not be complete; if the volume of the vacuum reaction chamber is too large, it will cause secondary reactions between the gas and iodide ions to form impurities, which will affect the sensitivity of the detection results.

Specifically, as shown in Figure 5, the quadrupole mass spectrometer system includes a collision dissociation chamber, a quadrupole mass spectrometer filter chamber and an ion detector, the collision dissociation chamber is connected with the vacuum reaction chamber of the chemical ionization system, and the collision dissociation chamber It is connected with the quadrupole mass spectrometer filter chamber, and the quadrupole mass spectrometer filter chamber is connected with the ion detector.

In a preferred embodiment of the present invention, the quadrupole mass spectrometer system is selected from quadrupole mass spectrometers. In some embodiments, the quadrupole mass spectrometer is selected from those manufactured by THS Instruments LLC in Georgia, USA.

Preferably, when the IHONO ^- polymerization ion is carried out mass spectrometry detection in the quadrupole mass spectrometry reaction chamber, its mass-to-nucleus ratio is 174, and the mass-spectrum signal intensity of the IHONO ^- polymerization ion can be detected at a mass-to-nucleus ratio of 174; the I ^- ion carries out mass spectrometry During detection, its mass-to-nucleus ratio is 127, and the mass-spectrum signal intensity of ^the I ^- ion can be detected when the mass-to-nucleus ratio is 127; The mass spectrum signal intensity of the IHCOOH ^- interfering ion can be detected, and the mass spectrum signal intensity is directly output by the result processing module.

Further preferably, according to the sensitivity of the ambient air sample, the background signal of the ambient air sample, the mass spectrum signal intensity of the IHONO-polymerization ion, the mass spectrum signal intensity and the background signal of the I-reagent ion, the mass spectrum signal intensity and the background signal of the IHCOOH-interfering ion Calculate the concentration of gaseous nitrous acid in the ambient atmosphere.

Further description will be given below with the content of specific embodiments.

Example 1

Acquisition of the calibration curve of sensitivity and humidity, the calibration curve of background signal and humidity

Set the pressure of the vacuum reaction chamber to 24torr, 50torr, 62torr, and 74torr respectively; provide a HONO calibration system, use a HONO generator to generate HONO standard gas, and dilute the HONO standard gas through a zero-gas humidity adjustment system with adjustable humidity to obtain different HONO gas with relative humidity, wherein, HONO gas with different relative humidity includes HONO gas with relative humidity of 20% to 80%, when the pressure is 24torr, the HONO gas with different relative humidity is selected from 20% to 80%; when the pressure is 50torr , the HONO gas with different relative humidity is selected from 20%～60%; when the pressure is 62torr, the HONO gas with different relative humidity is selected from 20%～70%; when the pressure is 74torr, the HONO gas with different relative humidity is selected from 20%～ 60%.

The chemical ionization mass spectrometer was used to detect the sensitivity and background signal of HONO gas under different pressure conditions and different relative humidity.

Result analysis:

Analyze the standard curve of HONO gas sensitivity drawn by different relative humidity and sensitivity of N groups, as shown in Figure 6, when the pressure is 24torr, HONO gas with different relative humidity is detected, and the equation related to HONO gas sensitivity and relative humidity Be y=1.2E-6e ^-0.007x ; When pressure is 50torr, the HONO gas of different relative humidity is detected, and the equation relevant to HONO gas sensitivity and relative humidity is y=5.1E-6e ^-0.022x ; When pressure is When 62torr, detect HONO gas with different relative humidity, the equation related to HONO gas sensitivity and relative humidity is y=6.0E-6e ^-0.023x ; when the pressure is 74torr, detect HONO gas with different relative humidity, HONO The equation related to gas sensitivity and relative humidity is y=7.0E-6e ^-0.024x .

The standard curve of drawing HONO gas background signal to N group different relative humidity and background signal is analyzed, as shown in accompanying drawing 7, when pressure is 62torr, HONO gas of different relative humidity is detected, HONO gas background signal and relative humidity The related equation is y=0.0043e ^-0.023x .

It can be seen that the sensitivity and background signal of the instrument for the measurement of HONO will decrease with the increase of relative humidity (RH). According to the different relative humidity, sensitivity and background signal of N groups, the standard curve of HONO gas sensitivity is an exponential decay curve. Since the pressure during the reaction will affect the reaction rate of I ^- and HONO, and the reaction rate of IHONO ^- and H ₂ O, the sensitivity and background signal will decrease with the reduction of the pressure during the reaction.

Example 2

Measurement and analysis of gaseous nitrous acid concentration in the ambient atmosphere

In December 2017, the concentration of gaseous nitrous acid in the ambient atmosphere was measured and analyzed in Wangdu area, Hebei Province

Provide a sampling system made of Teflon material to collect ambient air samples, so that the ambient air samples enter through the air inlet, pass through the collision cutter, and use the airflow with a flow rate of 12-15lpm to remove the impurities of the ambient air samples from the bypass port , adopt flow rate to be that the airflow of 1.5～2.5lpm collects the ambient air sample that contains HONO from the main crossing and measure; Adopt external humidity detector to measure the relative humidity of ambient air sample, adopt the equation of the HONO gas sensitivity that embodiment 1 obtains to calculate and obtain environment The sensitivity of the atmospheric sample adopts the equation calculation of the HONO gas background signal that embodiment 1 obtains to obtain the background signal of the ambient atmospheric sample;

In the chemical ionization mass spectrometer, the pressure of the ambient air sample is controlled to be 62torr, and the flow rate is 1.5slpm to flow into the molecular ion reaction chamber, wherein the molecular ion reaction formula is a cylinder made of 304 stainless steel, with a height of 5cm and an inner diameter of 6cm; In the molecular ion reaction chamber, provide methyl iodide and nitrogen to mix and prepare methyl iodide/nitrogen cylinder gas, control the flow rate of methyl iodide to 5 sccm, and the concentration is 3000 ppm; mix with nitrogen with a purity of ≥99.99% and a flow rate of 500 sccm Obtain a mixed gas; use ²¹⁰ Po radioactive sources to ionize the mixed gas to obtain iodide ions; react ambient air samples with iodide ions to obtain reactants;

Using a quadrupole mass spectrometer to measure the mass spectrum signal intensity of IHONO ^- polymerization ion in the reactant, the mass spectrum signal intensity and background signal of I ^- ion, IHCOOH ^- interfering ion, and calculate the concentration of HONO,

Result analysis:

Adopt quadrupole mass spectrometer to measure the mass spectrum signal intensity of IHONO ^- polymerization ion in the reactant respectively, the mass spectrum signal intensity of I ^- ion, IHCOOH ^- interfering ion, as shown in Figure 8, can, clearly analyze and obtain the IHONO ^- in the reactant The mass spectrum signal intensity of the polymerized ion, the mass spectrum signal intensity of the I ^- ion, IHCOOH ^- interfering ion, and the concentration of HONO is calculated by the following formula,

Among them, SIG _174/127 is the ratio of the mass spectrum signal intensity of the IHONO ^- polymerized ion to the mass spectrum signal intensity of the I ^- ion; the BKG _{ambient air sample} is the background signal of the ambient air sample calculated by using the equation of the HONO gas background signal; SIG _{173/ 127} is the ratio of the mass spectrum signal intensity of the IHCOOH ^- interfering ion to the mass spectrum signal intensity of the I ^- ion; BKG _173/127 is the ratio of the background signal of the IHCOOH ^- interfering ion to the background signal of the I ^- ion during the mass spectrometry; SENS _{ambient air sample} The sensitivity of ambient air samples is calculated by using the equation of HONO gas sensitivity; 1.2% (SIG _173/127 -BKG _173/127 ) is the ratio of ¹³ C isotope signal of formic acid.

Through calculation, the concentration of gaseous nitrous acid HONO in the ambient atmosphere in Wangdu area of Hebei Province is 80-8200ppt.

Example 3

Interfering substance test test

Using the process of measuring and analyzing the concentration of gaseous nitrous acid in the ambient atmosphere in Example 2, NO, NO ₂ and HNO ₃ and other gases are added to the sampling pipeline, and other operating steps are consistent with Example 2.

Result analysis:

The test results are shown in Table 1 below. The content of NO and HNO ₃ is lower than the detection limit and cannot be detected and processed, so it will not affect the monitored HONO concentration at all. Whereas only about 0.5% of _NO2 will be converted to HONO, with negligible influence on the measurement of HONO concentration.

Table 1

*U.D. means lower than the detection limit (30ppt)

Example 4

High time resolution measurement and response time measurement

Pass HONO gas into the device and test its response time.

Result analysis:

As shown in Figure 9, the HONO gas responds very quickly in the equipment, and the response time is less than 1s. At the same time, the HONO gas will not form adhesion on the inner wall of the equipment and sampling pipeline, resulting in hysteresis effect. Since this monitoring method does not require pretreatment of the sample, the chemical ionization reaction responds very quickly, and the mass spectrometer is used as a detector. This method can realize high time-resolved monitoring and fast response of HONO gas.

Comparative example 1

Measurement and Analysis of Gaseous Nitrite Concentration in Ambient Atmosphere Using LOPAP Instrument

In December 2017, the concentration of gaseous nitrous acid in the ambient atmosphere was measured and analyzed in Wangdu area, Hebei Province

The LOPAP instrument was used to measure and analyze the concentration of gaseous nitrous acid in the ambient atmosphere in Wangdu area, Hebei Province in December 2017, and compare and analyze the measurement results with the measurement results of Example 2.

Result analysis:

As shown in accompanying drawing 10, the measurement result of embodiment 2 (CIMS) is basically consistent with the concentration of HONO gas of comparative example 1 (LOPAP instrument), and the HONO concentration that two instruments measure is basically consistent, and ^R up to 0.9. The feasibility of this method is confirmed. It shows that the measurement method provided by Example 2 of the present invention has high accuracy, and the method provided by Example 2 can be used to test HONO gas in the atmosphere.

The above are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention. Inside.

Claims (10)

1. The method for measuring the concentration of the gaseous nitrous acid in the environment atmosphere is characterized by comprising the following steps of:

determining instrument sensitivity and background signal: determining the pressure of a vacuum reaction chamber, and diluting the HONO standard gas by N groups of zero gas with different relative humidity to obtain N groups of HONO standard gas with different relative humidity, wherein N is more than or equal to 5; respectively detecting the sensitivity and background signals of the HONO gas with N groups of different relative humidity, drawing a standard curve of the HONO gas sensitivity according to the N groups of different relative humidity and the sensitivity, obtaining an equation of the HONO gas sensitivity, drawing a standard curve of the HONO gas background signal according to the N groups of different relative humidity and the background signal, and obtaining an equation of the HONO gas background signal;

Collecting an atmospheric sample: collecting an environmental atmosphere sample, measuring the relative humidity of the environmental atmosphere sample, calculating the sensitivity of the environmental atmosphere sample by adopting the equation of the HONO gas sensitivity, and calculating the background signal of the environmental atmosphere sample by utilizing the equation of the HONO gas background signal;

calculating the HONO concentration: providing iodide ions to a vacuum reaction chamber, controlling the flow of the environmental atmosphere sample entering the vacuum reaction chamber through a sampling pipeline, reacting the environmental atmosphere sample with the iodide ions to obtain a reactant, and measuring IHONO in the reactant ^- Mass spectrum signal intensity of polymeric ions, I ^- Reagent ions, IHCOOH ^- Mass spectrum signal intensity of interfering ions and background signal; and calculating the concentration of the gaseous nitrous acid in the environment atmosphere according to a calculation formula of the concentration of the gaseous nitrous acid.

2. The method for measuring the concentration of gaseous nitrous acid in the ambient atmosphere according to claim 1, wherein the calculation formula of the concentration of gaseous nitrous acid is:

wherein SIG _174/127 For said IHONO ^- Mass spectral signal intensity of polymeric ions with the I ^- Ratio of mass spectral signal intensities of reagent ions; BKG _{Environmental atmosphere sample} A background signal for the ambient atmosphere sample; SIG (SIG) _173/127 For said IHCOOH ^- Mass spectrum signal intensity of interfering ion and I ^- Ratio of mass spectral signal intensities of reagent ions; BKG _173/127 For said IHCOOH ^- Background signal of interfering ion and the I ^- A ratio of background signals of reagent ions; SENS _{Environmental atmosphere sample} Sensitivity for the ambient atmospheric sample; 1.2% (SIG) _173/127 -BKG _173/127 ) Is in formic acid ¹³ Signal intensity of C isotope ratio.

3. The method for measuring the concentration of gaseous nitrous acid in ambient atmosphere according to claim 1, wherein in the step of providing iodide ions, a mixed gas of methyl iodide and nitrogen is ionized by an alpha radiation source in the ion source to obtain iodide ions; wherein the alpha radiation source is selected from ²¹⁰ Po、 ²²⁶ Ra、 ²²⁸ Th、 ²³⁸ Pu、 ²³⁹ Pu、 ²⁴¹ Am.

4. The method for measuring the concentration of gaseous nitrous acid in ambient atmosphere according to claim 3, wherein the flow rate of the methyl iodide is 1 to 10sccm, and the concentration of the methyl iodide is 3000 to 4000ppm; and/or the number of the groups of groups,

the flow rate of the nitrogen is 100-1000 sccm, and the purity of the nitrogen is more than or equal to 99.99%.

5. The method for measuring the concentration of gaseous nitrous acid in an ambient atmosphere according to any one of claims 1 to 4, wherein in the step of determining the pressure of the vacuum reaction chamber, the pressure of the vacuum reaction chamber is 20 to 80torr; and/or the number of the groups of groups,

In the step of controlling the flow rate of the environmental atmosphere sample entering the vacuum reaction chamber through the sampling pipeline, the flow rate of the environmental atmosphere sample entering the vacuum reaction chamber through the sampling pipeline is 0.5-2.0 slpm.

6. The method according to any one of claims 1 to 4, wherein in the step of reacting the ambient atmosphere sample with the iodide ions to obtain a reactant, the reaction step is performed in a vacuum reaction chamber, wherein the vacuum reaction chamber is made of 304 stainless steel, and the vacuum reaction chamber is cylindrical in shape.

7. The method for measuring the concentration of gaseous nitrous acid in ambient atmosphere according to claim 6, wherein the length of the vacuum reaction chamber is 3 to 10cm and the inner diameter is 4 to 8cm.

8. A method for measuring the concentration of gaseous nitrous acid in an ambient atmosphere according to any one of claims 1 to 4, characterized in that,

in the step of reacting the environmental atmosphere sample with the iodide ions to obtain a reactant, a chemical ionization system is adopted for reaction; and/or the number of the groups of groups,

determining IHONO in the reactant ^- Mass spectrum signal intensity of polymeric ions, I ^- Reagent ions, IHCOOH ^- In the step of interfering the mass spectrum signal intensity of the ion and the background signal, a quadrupole mass spectrum system is adopted for measurement.

9. The measuring system is characterized by comprising a calibration system, a sampling system, a chemical ionization system and a quadrupole mass spectrometry system, wherein the calibration system is connected with the chemical ionization system, the sampling system is connected with the chemical ionization system, and the chemical ionization system is connected with the quadrupole mass spectrometry system;

the calibration system comprises a zero gas generator, an acid scrubber, a HONO generator, a humidity controller, a humidity sensor, a sampling tube and a bypass tube, wherein the zero gas generator is connected with the HONO generator;

the sampling system comprises a main air inlet pipe, a particle separator, a bypass pipe and an instrument air inlet pipe, wherein the main air inlet pipe is connected with the bypass pipe and the instrument air inlet pipe through the particle separator, and the instrument air inlet pipe is connected with a vacuum reaction chamber of the chemical ionization system;

The chemical ionization system comprises an ion source and a vacuum reaction chamber, wherein the ion source is connected with the vacuum reaction chamber, and the vacuum reaction chamber is connected with a collision dissociation chamber of the quadrupole mass spectrometry system;

the quadrupole mass spectrometry system comprises a collision dissociation chamber, a quadrupole mass spectrometry filter chamber and an ion detector, wherein the collision dissociation chamber is connected with the quadrupole mass spectrometry filter chamber, and the quadrupole mass spectrometry filter chamber is connected with the ion detector.

10. The system for measuring the concentration of gaseous nitrous acid in the ambient atmosphere according to claim 9, wherein the materials of the main air inlet pipe, the bypass pipe and the instrument air inlet pipe in the sampling system are selected from teflon materials.