CN114166920B - Method and system for measuring concentration of gaseous nitrous acid in ambient atmosphere - Google Patents
Method and system for measuring concentration of gaseous nitrous acid in ambient atmosphere Download PDFInfo
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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
Technical Field
The invention relates to the field of analysis and detection, in particular to a method and a system for measuring the concentration of gaseous nitrous acid in ambient atmosphere.
Background
Gaseous nitrous acid (HONO) is an important source of classical oxidant hydroxyl radicals (OH) in the atmospheric environment, can directly influence the atmospheric oxidizing capacity, further controls the formation of secondary pollutants such as dust haze, ozone, etc., and thus becomes an important substance in the research of atmospheric chemistry and atmospheric pollution cause. In the atmosphere, gaseous nitrous acid (HONO) has a very high chemical activity, although its concentration is usually very low, between 0.1 and 10 ppb. During the day, 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 the photolysis is particularly important in polluted areas, and recent scientific researches show that the photolysis of HONO in the polluted areas can contribute up to 80% of OH free radicals. OH radicals are important classical oxidants in the atmosphere and are core materials in atmospheric chemistry and air quality research, which oxidize Volatile Organic Compounds (VOCs), carbon monoxide (CO), nitrogen Oxides (NO) x ) Sulfur dioxide (SO) 2 ) Etc., thereby affecting the production of a variety of contaminants, including secondary aerosols, ozone (O 3 ) And dioxygenCarbon (CO) 2 ). However, the direct measurement of OH free radicals is difficult due to the characteristics of strong activity, low concentration, short service life and the like, so that the precursor (mainly HONO, O 3 And aldehydes) are important means for analyzing the concentration of OH radicals, for performing atmospheric oxidizing studies and for analyzing the cause of atmospheric pollutants.
At present, the source of gaseous nitrous acid is relatively complex. Known source awareness includes direct emissions from motor vehicles, nitrogen dioxide (NO 2 ) The heterogeneous transformation of (2) is complicated in source conditions such as soil release and nitrate photolysis, and is unfavorable for one-to-one analysis. However, recent studies have also shown that there is an unknown source of HONO found in the daytime and that the mechanism of HONO generation in the atmosphere is not clearly known, so that an instrument and method capable of experimentally and rapidly and accurately measuring HONO are needed to further explore the source of HONO, the chemical mechanism and its influence in the atmosphere.
Currently, there are many methods for determining the concentration of HONO in the atmosphere, including spectroscopy and wet chemistry. The spectrometry is a classical method for measuring the HONO concentration, but the detection limit of a spectrometer is generally high, generally about hundreds ppt, and the stability of the spectrometer in an external field experiment is poor, so that the spectrometer is not beneficial to analyzing the atmospheric HONO concentration with low content, and is generally suitable for laboratory research. The wet chemical method is characterized by lower detection limit, and one of the very successful commercial instruments is long-path absorption spectroscopy (lopp) from QUMA, germany, which is based on two-channel sampling and long-path absorption colorimetric determination, and can effectively eliminate interference and achieve lower detection limit (about 10 ppt). However, since HONO is absorbed by the absorbing liquid and then needs to pass through a long liquid path, the response time of the instrument is long (several minutes), and the time resolution used for atmospheric measurement is usually ten minutes, so that the measurement time is long. In addition, the LOPAP instrument is expensive to sell, cumbersome to maintain, prone to failure due to liquid leakage, and affects equipment safety and wide use.
Disclosure of Invention
The application aims to provide a method and a system for measuring the concentration of gaseous nitrous acid in the environment atmosphere, and aims to solve the problems of low response speed, poor sensitivity and complex operation of the method for measuring the concentration of the gaseous nitrous acid in the environment atmosphere in the prior art.
In order to achieve the above purpose, the application adopts the following technical scheme:
in a first aspect, the application provides a method for measuring the concentration of gaseous nitrous acid in an ambient atmosphere, comprising the 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.
In a second aspect, the application provides a measurement system for the concentration of gaseous nitrous acid in ambient atmosphere, the measurement system comprises a calibration system, a sampling system, a chemical ionization system and a quadrupole mass spectrometry system, 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.
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 adopted as a reaction reagent, and as the reactivity of the iodide ions with water is very strong, the humidity in the environment can influence the sensitivity of the reaction, so that before a sample is analyzed, the sensitivity of an instrument is calibrated by utilizing HONO standard gas generated by a HONO generator under the pressure condition of a certain vacuum reaction chamber, the sensitivity and background signals of the HONO gas obtained by diluting different relative humidity are calibrated, N is more than or equal to 5, and a certain number of samples with different humidity can be ensured to draw standard curves of 'relative humidity-HONO gas sensitivity' and 'relative humidity-HONO gas background signal', so as to carry out subsequent sampling analysis.
Secondly, directly collecting an environmental atmosphere sample for analysis, and ensuring that HONO gas with low concentration can be detected without pretreatment or concentration of the environmental atmosphere sample; reacting the environmental atmosphere sample to be detected with iodide ions, and carrying out addition reaction with HONO gas in the environmental atmosphere sample to be detected to form IHONO - Polymerizing ions and measuring IHONO in the reactant - And further calculating the information such as mass spectrum signal intensity of the polymer ions and the impurity ions to obtain the concentration of HONO.
The test method can be used for measuring the low-concentration gaseous nitrous acid with the detection limit of tens ppt level, so that the test method has higher sensitivity; the detection process is different from the traditional wet chemical method, 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.
The measuring system comprises a calibration system, a sampling system, a chemical ionization system and a quadrupole mass spectrometry system, wherein the measuring system is used for measuring the concentration of the gaseous nitrous acid in the ambient atmosphere, the measuring speed is high, the sensitivity is high, the interference is small, consumable materials which are frequently replaced are not needed in the whole measuring system, the possible harm of solution leakage to electronic equipment is not needed in design, the operation is simple and convenient, the operation and maintenance workload is small, the use is safe, and the measuring system is favorable for being widely applied to HONO measurement of the outdoor ambient atmosphere.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the embodiments or the description of the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of a system for measuring the concentration of gaseous nitrous acid in an ambient atmosphere according to an embodiment of the present application.
FIG. 2 is a schematic diagram of a calibration system provided by an embodiment of the present application.
Fig. 3 is a schematic diagram of a sampling system according to an embodiment of the present application.
Fig. 4 is a schematic diagram of a chemical ionization system provided by an embodiment of the present application.
Fig. 5 is a schematic diagram of a quadrupole mass spectrometry system according to an embodiment of the application.
Fig. 6 is a calibration curve of HONO gas sensitivity plotted against different relative humidity and sensitivity provided by an embodiment of the present application.
Fig. 7 is a standard curve of the HONO gas background signal plotted against humidity versus background signal for different embodiments of the present application.
Fig. 8 is a graph of ion mass spectrum signals for environmental atmospheric measurements provided in example 2 of the present application.
Fig. 9 is a response time measurement result of HONO gas provided in example 4 of the present invention.
FIG. 10 shows the measurement results of example 2 (CIMS) provided in comparative example 1 of the present invention and the measurement results of HONO gas in comparative example 1 (LOPAP instrument).
Detailed Description
In order to make the objects, technical solutions and technical effects of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art without the exercise of inventive faculty, are intended to be within the scope of the invention in connection with the embodiments herein.
In the description of the present invention, it should be understood that the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature. In the description of the present invention, the meaning of "a plurality" is two or more, unless explicitly defined otherwise.
The embodiment of the invention provides a method for measuring the concentration of gaseous nitrous acid in ambient atmosphere, which comprises the following steps:
s01, determining the sensitivity of the instrument and a 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 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 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 background signal, and obtaining an equation of the HONO gas background signal;
s02, 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 an equation of HONO gas sensitivity, and calculating the background signal of the environmental atmosphere sample by utilizing an equation of HONO gas background signal;
s03, calculating HONO concentration: providing iodide ions to the vacuum reaction chamber, controlling the flow of the environmental atmosphere sample entering the vacuum reaction chamber through the 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.
According to the method for testing the concentration of the gaseous nitrous acid in the environment atmosphere, disclosed by the invention, the method of directly sampling and utilizing the chemical ionization mass spectrum is used for rapidly measuring, the response time is rapid, the change of the gaseous nitrous acid in a short time can be effectively and accurately observed, and a foundation is provided for better analyzing the atmospheric oxidability and pollution cause; 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 is different from the traditional wet chemical method, 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.
Specifically, in the step S01, the instrument sensitivity and the background signal are determined. 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; according to the method, iodide ions are used as a reaction reagent, the reactivity of the iodide ions and water is very strong, the humidity in the environment can influence the sensitivity of the reaction, and therefore, before a sample is analyzed, the sensitivity and the background signal of the HONO gas obtained by diluting different relative humidities are analyzed under the condition of a certain vacuum reaction chamber pressure, N is more than or equal to 5, and the fact that the sample with a certain number of different humidities can draw the standard curves of the relative humidity-HONO gas sensitivity and the relative humidity-HONO gas background signal is ensured.
Specifically, because the pressure of the vacuum reaction chamber in the system has a certain influence on the detection sensitivity, the sensitivity is different under the pressure systems of different vacuum reaction chambers, so that the pressure of the vacuum reaction chamber is determined to be a certain condition for testing, and the pressure value of the vacuum reaction chamber is ensured to be consistent with the pressure of the vacuum reaction chamber in the subsequent sampling process, so that the sensitivity of the environmental atmosphere sample and the background signal of the environmental atmosphere sample are conveniently calculated.
Preferably, in the step of determining the pressure of the vacuum reaction chamber, the pressure of the vacuum reaction chamber is 20 to 80torr. In an embodiment of the present invention, the control pressure is 62torr. Further, at a pressure of 62torr, other important atmospheric oxidizer precursors including NO can be effectively monitored simultaneously 3 Radical precursor N 2 O 5 Cl radical precursor (ClNO 2 、Cl 2 And BrCl) and Br radical precursor (Br) 2 And HOBr) and the like, thereby greatly increasing the application range.
Preferably, the relative humidity is 20% to 80%. Under the humidity conditions, the influence of different relative humidities on the detection of the HONO gas can be analyzed. Wherein, relative humidity refers to the percentage of water vapor pressure in air to saturated water vapor pressure at the same temperature.
Preferably, under certain pressure conditions, the influence of different relative humidities on the detection of the HONO gas is analyzed using a calibration system.
Preferably, as shown in fig. 2, the calibration system comprises a zero gas generator (1), an acid scrubber (2), a HONO generator (3), a humidity controller (4), a humidity sensor (5), a sampling pipe (6) and a calibration bypass pipe (7). The zero gas generator is connected with the HONO generator, the acid scrubber is connected with the HONO generator, the HONO generator is connected with the sampling tube, the humidity controller is connected with the HONO generator in parallel, one end of the humidity sensor is connected between the HONO generator and the sampling tube, the other end of the humidity sensor is connected with the bypass tube, and the output end of the sampling tube is connected with the vacuum reaction chamber of the chemical ionization system.
In some embodiments, the zero gas generator is selected from Model 111 manufactured by Thermo corporation, and the zero gas generated is required to be further stripped of minute amounts of HONO gas by an acid gas absorption box containing glass fibers covered with sodium carbonate.
In some embodiments, the HONO generator is produced by QUMA, germany, and comprises a spiral tube reactor and cooling circulating water.
In some embodiments, the humidity controller is configured to regulate the humidity of the zero gas, and further to control the effect of different relative humidities on the detection of the 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 for measuring the humidity of the introduced HONO standard gas.
The output end of the sampling tube is connected with a vacuum reaction chamber of the chemical ionization system, and HONO standard gas is introduced into the chemical ionization system for analysis.
In some embodiments, in the process of gas calibration by adopting a calibration system, dilute sulfuric acid (1M) solution and nitrous acid solution in an acid scrubber are pumped into a spiral tube reactor of a HONO generator through a peristaltic pump according to a fixed flow rate, and are reacted after mixing to generate nitrous acid, and the nitrous acid is blown out by 2L/min of zero gas provided by the zero gas generator; the humidity controller is adopted for adjustment, diluted zero gas with the total flow of 8L/min provided by the zero gas generator passes through two paths respectively, one path passes through the bubble device for humidification, the other path does not pass through humidification, the humidity sensor is utilized for detecting zero gas humidity loaded with nitrous acid gas, the zero gas humidity is mixed with 2L/min nitrous acid gas generated by the HONO generator to obtain mixed gas, and then the mixed gas is introduced into the quadrupole mass spectrometry system through the sampling pipe for analyzing the sensitivity condition of the HONO gas under different humidity.
In a preferred embodiment of the present invention, a calibration system is provided to dilute the HONO gas through N sets of environments with different relative humidities to obtain N sets of HONO gases with different relative humidities, and to detect the sensitivity and background signal of the N sets of HONO gases with different relative humidities, respectively. Further, a chemical ionization system is used to detect the sensitivity and background signal of the HONO gas at different relative humidities.
Specifically, drawing a standard curve of HONO gas sensitivity according to N groups of different relative humidity and sensitivity, obtaining an equation of HONO gas sensitivity, drawing a standard curve of HONO gas background signal according to N groups of different relative humidity and background signal, and obtaining HONO gas background signalEquation (d). Wherein due to the water molecules in the air and IHONO - The ions undergo reversible reactions as shown in the following reaction formula:thus, the sensitivity of the instrument to the measurement of HONO and the background signal decrease with increasing Relative Humidity (RH), and the standard curve of HONO gas sensitivity is plotted as an exponential decay curve from the N sets of different relative humidity and sensitivity and background signal. Since the pressure during the reaction will affect I at the same time - Reaction Rate with HONO and IHONO - And H is 2 The reaction rate of O, and therefore the sensitivity and background signal, is reduced with a decrease in gas pressure during the reaction, but the influence of RH is slowed down.
In the above step S02, an atmospheric sample is collected. The method comprises the steps of collecting an ambient air sample and measuring the relative humidity of the ambient air sample, and preferably, carrying out aerosol particle removal on the collected ambient air sample, so that the accumulation of aerosol particles in the atmosphere in a sampling pipeline is reduced, the HONO measurement is interfered, the detection of low-concentration HONO gas is ensured, the detection method can be used for measuring low-concentration gaseous nitrous acid, the detection limit is tens ppt, and the high sensitivity and the less interference are ensured.
Preferably, as shown in fig. 3, the sampling system comprises a main air inlet pipe (1), a particle separator (4), a bypass pipe (2) and an instrument feed pipe (3). 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 the chemical ionization system; after the gas enters the system from the gas inlet, the gas reaches the particle separator through the total sample injection pipe, so that aerosol particles in the gas are removed, and the aerosol particles are removed from the bypass port; and leading out the gas from which the sol particles are removed to a chemical ionization system through an instrument sample injection pipe for subsequent analysis.
Preferably, the material of the sampling system is selected from Teflon materials, and the sampling system prepared from the Teflon materials is provided for collecting an environmental atmosphere sample and is matched with a particle separator to remove aerosol particles of the environmental atmosphere sample; the sampling system is adopted to collect samples and remove aerosol particles, so that the deposition of the aerosol particles on the wall of the sampling tube can be reduced, and the pipeline interference caused by the heterogeneous reaction of the pipeline is avoided.
Preferably, in the step of collecting the ambient atmosphere sample by using the sampling system, the ambient atmosphere sample is introduced through the air inlet, aerosol particles of the ambient atmosphere sample are removed from the bypass pipe by using an air flow with a flow rate of 12-15 lpm through the particulate matter separator, and the ambient atmosphere sample containing HONO is collected from the ambient atmosphere sample collection pipe by using an air flow with a flow rate of 1.5-2.5 lpm. Under the above conditions, the sampling system comprising the particle separator is adopted, and meanwhile, the large-flow air flow is utilized, so that the atmospheric aerosol particles in the atmospheric sample can be ensured to be discharged from the bypass port, and then, the small-flow air flow is adopted, the HONO-containing environmental atmospheric sample obtained by degassing the aerosol particles is collected and subjected to instrument detection, so that the sample is ensured to be free from heterogeneous reaction interference of the aerosol particles, and the detection of low-concentration HONO gas is facilitated.
Preferably, the external humidity detector is used for measuring the relative humidity of the environmental atmosphere sample, the measured relative humidity value is calculated by adopting an equation of HONO gas sensitivity to obtain the sensitivity of the environmental atmosphere sample, and the equation of HONO gas background signal is used for calculating to obtain the background signal of the environmental atmosphere sample so as to carry out subsequent tests.
In the above step S03, the HONO concentration is calculated. Providing iodide ions to the vacuum reaction chamber; preferably, in the step of supplying iodide ions, the mixed gas of methyl iodide and nitrogen is ionized in an ion source by an alpha radiation source selected from the group consisting of 210 Po、 226 Ra、 228 Th、 238 Pu、 239 Pu、 241 Am.
Preferably, as shown in FIG. 4, the chemical ionization system includes an ion source and a vacuum reaction chamber. The ion source is connected with a vacuum reaction chamber, and the vacuum reaction chamber is connected with a 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 prepared by the georgia THS Instruments LLC study in the united states.
In some embodiments, in the chemical ionization system, an α -radiation source is adopted to quickly ionize to obtain iodide ions, and an environmental atmosphere sample to be tested reacts with the iodide ions, and the iodide ions have a strong electron affinity and react with HONO gas in the environmental atmosphere sample to be tested in an addition reaction of the following reaction formula: i - +HONO+M＝IHONO - +M, reaction to form IHONO - The method for detecting the polymeric ions can effectively and accurately observe the change of the gaseous nitrous acid in a short time due to rapid release of iodide ions, rapid reaction with a sample for measurement and rapid response time.
Preferably, methyl iodide (CH 3 I) Ionization is carried out to obtain iodide ions, and the iodide ions are subjected to addition reaction with HONO gas in an environmental atmosphere sample to be detected to form IHONO - And the polymer ions are favorable for measuring the concentration of the HONO gas, and iodide ions are adopted as the reactive ions. In the preferred embodiment of the invention, methyl iodide and nitrogen are mixed to prepare methyl iodide/nitrogen steel cylinder gas for use.
Preferably, the flow rate of methyl iodide is 1-10 sccm, and the concentration of methyl iodide is 3000-4000 ppm. The flow and the concentration of methyl iodide are controlled, so that the subsequent ionization can be ensured to obtain iodine ions with proper concentration. If the flow or concentration of methyl iodide is too low, iodide ions cannot be rapidly generated in the process of ionization treatment by adopting an alpha radioactive source, so that the response time of detection is influenced, and the detection time is longer; if the flow rate or the concentration of the methyl iodide is too high, the methyl iodide is in a liquid state at room temperature, so that the methyl iodide is easy to remain in the pipe wall, and the detection sensitivity is affected.
Preferably, the nitrogen gas is mixed with methyl iodide for the purpose of adjusting the concentration of methyl iodide to make the ionization effect better. Preferably, the flow rate of the nitrogen is 100-1000 sccm, the purity of the nitrogen is more than or equal to 99.99 percent, the flow rate of the nitrogen is controlled to be larger, and the nitrogen is mixed with methyl iodide to further adjust the methyl iodideIs favorable for subsequent rapid ionization to obtain iodide ions; the purpose of selecting high-purity nitrogen with purity of 99.99% is to reduce O 2 - The generation of ions, and thus the interference, is avoided.
Preferably, the mixed gas is ionized by an alpha radioactive source to obtain iodide ions, wherein the alpha radioactive source is made of nuclide emitting alpha particles and is characterized by emitting the alpha particles. Preferably, the alpha radiation source is selected from 210 Po、 226 Ra、 228 Th、 238 Pu、 239 Pu、 241 Any one of Am is selected to test, and the iodine ions can be obtained by rapid ionization. In a preferred embodiment of the invention, the selection is 210 Po was tested.
Further, the flow rate of the environmental atmosphere sample entering the vacuum reaction chamber through the sampling pipeline is controlled, and as the pressure and the flow rate of the vacuum reaction chamber obtained by sampling are large, if the pressure and the flow rate are too large in the process of reacting with iodide ions in the vacuum reaction chamber, the iodide ions can be quickly neutralized, the iodide ions can not be ensured to react with HONO gas only, and the reactant can not be ensured to comprise IHONO only - The polymerization of ions can form other reactive impurities that affect the sensitivity of the assay. In some embodiments, the flow of the ambient atmosphere sample through the sampling line into the vacuum reaction chamber is controlled by a restrictive orifice.
Preferably, 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, the pressure and the flow rate of the environmental atmosphere sample are controlled to be smaller, the reaction with iodide ions is ensured to be complete, and only IHONO is generated in the product - And the polymer ions are favorable for subsequent determination, and the higher sensitivity is ensured.
Specifically, an environmental atmosphere sample reacts with iodide ions to obtain a reactant, and the reactant and HONO gas in the environmental atmosphere sample undergo an addition reaction, wherein the reaction formula of the addition reaction is as follows: i - +HONO+M＝IHONO - +M, reaction to form IHONO - And polymerizing ions.
Preferably, in the step of reacting the ambient atmosphere sample with iodide ions to obtain a reactant, 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 a reactant, the reaction step is performed in a vacuum reaction chamber of the chemical ionization system, wherein the vacuum reaction chamber is made of 304 stainless steel, and the vacuum reaction chamber is cylindrical in shape. In some embodiments, the vacuum reaction chamber made of 304 stainless steel is selected for reaction, and as the 304 stainless steel has good corrosion resistance, heat resistance, low-temperature strength and mechanical properties, and good hot workability such as stamping, bending and the like, no heat treatment hardening phenomenon exists, the vacuum reaction chamber made of 304 stainless steel can improve the impurity doping free in the reaction process, and the reaction accuracy is improved; meanwhile, the reaction chamber is also ensured to be durable and can be reused. In other embodiments, the vacuum reaction chamber is cylindrical in shape, and a cylindrical reaction type is adopted, so that gas circulation is facilitated, response time is improved, contact between gas and a pipe wall is reduced, and reaction rate is ensured.
Further preferably, the length of the vacuum reaction chamber is 3 to 10cm and the inner diameter is 4 to 8cm. If the volume of the vacuum reaction chamber is too small, the reaction time is insufficient, and the reaction is incomplete; if the volume of the vacuum reaction chamber is too large, secondary reaction between the gas and iodide ions can be caused to form impurities, which affects the sensitivity of the detection result.
Preferably, IHONO is measured in the reaction - Mass spectrum signal intensity of polymeric ions, I - Ion, 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.
Preferably, as shown in fig. 5, the quadrupole mass spectrometry system comprises a collision dissociation chamber, a quadrupole mass spectrometry filter chamber, and an ion detector. The collision dissociation chamber is connected with a vacuum reaction chamber of the chemical ionization system, the collision dissociation chamber is connected with a quadrupole mass spectrum filter chamber, and the quadrupole mass spectrum filter chamber is connected with an ion detector.
In a preferred embodiment of the invention, the quadrupole mass spectrometry system is selected from quadrupole mass spectrometers. In some embodiments, the quadrupole mass spectrometer is selected from those prepared by the georgia THS Instruments LLC institute of america.
Preferably IHONO - When the mass spectrum detection is carried out on the polymer ions, the mass-to-core ratio is 174, and IHONO can be detected under the condition that the mass-to-core ratio is 174 - Mass spectrum signal intensity of the polymeric ions; i - When the mass spectrum detection is carried out on the ions, the mass-to-core ratio is 127, and the I can be obtained by detection under the condition that the mass-to-core ratio is 127 - Mass spectrum signal intensity of ions; IHCOOH (IH) - When the interference ion is detected by mass spectrum, the mass-to-core ratio is 173, and IHCOOH can be detected under the condition that the mass-to-core ratio is 173 - Interfering with the mass spectrum signal intensity of the ions.
Specifically, the concentration of the gaseous nitrous acid in the environment atmosphere is calculated according to a calculation formula of the concentration of the gaseous nitrous acid. Preferably, IHONO is performed based on the sensitivity of the ambient air sample, the background signal of the ambient air sample, and the sensitivity of the ambient air sample - Mass spectrum signal intensity, I of polymeric ions - Mass spectrum signal intensity of reagent ions, background signal, IHCOOH - And calculating the mass spectrum signal intensity of the interfering ions and the background signal to obtain the concentration of gaseous nitrous acid in the environment atmosphere.
Wherein the concentration of gaseous nitrous acid in the ambient atmosphere and IHONO in the measured reactant - The mass spectrum signal intensity of the polymeric ions is in a proportional relationship, and IHONO is measured in the reactant to avoid the influence of impurity ions in a chemical ionization mass spectrometer - Mass spectrum signal intensity of polymeric ions needs to be matched with reagent ions I - The ions are normalized and corrected, and IHCOOH needs to be considered - Interfering ions 13 The interference of the C isotope signal on the HONO signal also needs to consider the background signal and the correction curve of sensitivity and relative humidity of HONO gas in the environmental atmosphere sample.
Preferably, the calculation formula of the gaseous nitrous acid concentration is:
wherein SIG 174/127 Is IHONO - Mass spectrum signal intensity of polymeric ions and I - Ratio of mass spectral signal intensities of reagent ions; BKG Environmental atmosphere sample Background signal for ambient atmosphere sample; SIG (SIG) 173/127 For IHCOOH - Mass spectrum signal intensity of interfering ions and I - Ratio of mass spectral signal intensities of reagent ions; BKG 173/127 For IHCOOH - Background Signal of interfering ion and I - A ratio of background signals of reagent ions; SENS Environmental atmosphere sample Sensitivity for ambient atmospheric samples; 1.2% (SIG) 173/127 -BKG 173/127 ) Is in formic acid 13 Signal intensity of C isotope ratio.
The test method can effectively and accurately observe the change of the gaseous nitrous acid in a short time by directly sampling and rapidly measuring, and the detection method can measure the gaseous nitrous acid with low concentration, has the detection limit of tens ppt level and ensures higher sensitivity; the detection process is different from the traditional wet chemical method, 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.
Correspondingly, the embodiment of the invention also provides a system for measuring the concentration of the gaseous nitrous acid in the environment atmosphere, which comprises a sampling system, a chemical ionization system and a quadrupole mass spectrum system which are sequentially connected.
The invention provides a system for measuring the concentration of gaseous nitrous acid in ambient atmosphere, which is shown in figure 1 and comprises 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 measuring system is used for measuring the concentration of the gaseous nitrous acid in the environment atmosphere, the measuring speed is high, the sensitivity is high, the interference is small, consumable materials which are required to be replaced frequently do not exist in the whole measuring system, the possible harm to electronic equipment caused by solution leakage is not required to be worried in design, the operation is simple and convenient, the operation and maintenance workload is small, the use is safe, and the measuring system is favorable for widely applied to the gas detection of the outdoor environment atmosphere.
Specifically, the calibration system is included in the measurement system of the concentration of the gaseous nitrous acid in the environment atmosphere, and the influence of different relative humidity on the detection of the HONO gas can be analyzed by adopting the calibration system, so that the sensitivity of detecting the HONO gas can be further determined.
Specifically, as shown in fig. 2, the calibration system comprises a zero gas generator (1), an acid scrubber (2), a HONO generator (3), a humidity controller (4), a humidity sensor (5), a sampling pipe (6) and a bypass pipe (7). The zero gas generator is connected with the HONO generator, the acid scrubber is connected with the HONO generator, the HONO generator is connected with the sampling tube, the humidity controller is connected with the HONO generator in parallel, one end of the humidity sensor is connected between the HONO generator and the sampling tube, the other end of the humidity sensor is connected with the bypass tube, and the output end of the sampling tube is connected with the vacuum reaction chamber of the chemical ionization system.
In some embodiments, the zero gas generator is selected from Model 111 manufactured by Thermo corporation, and the zero gas generated is required to be further stripped of minute amounts of HONO gas by an acid gas absorption box containing glass fibers covered with sodium carbonate.
In some embodiments, the HONO generator is produced by QUMA, germany, and comprises a spiral tube reactor and cooling circulating water.
In some embodiments, the zero gas generator is configured to adjust the humidity of the zero gas, and further to control the effect of different relative humidities on the detection of the 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 for controlling the humidity of the nitrous acid gas being fed;
furthermore, the output end of the sampling tube is connected with the chemical ionization system, and HONO standard gas is directly introduced into the chemical ionization system for calibration.
In some embodiments, in the process of gas calibration by adopting a calibration system, dilute sulfuric acid (1M) solution and nitrous acid solution in an acid scrubber are pumped into a spiral tube reactor of a HONO generator through a peristaltic pump according to a fixed flow rate, and are reacted after mixing to generate nitrous acid, and the nitrous acid is blown out by 2L/min of zero gas provided by the zero gas generator; the humidity controller is adopted for adjustment, diluted zero gas with the total flow of 8L/min provided by the zero gas generator passes through two paths respectively, one path passes through the bubble device for humidification, the other path does not pass through humidification, the humidity sensor is utilized for detecting the humidity of nitrous acid gas, the nitrous acid gas is mixed with 2L/min nitrous acid gas generated by the HONO generator to obtain mixed gas, and then the mixed gas is introduced into the chemical ionization system through the sampling pipe for analyzing the sensitivity condition of the HONO gas under different humidity.
In a preferred embodiment of the present invention, a calibration system is provided to dilute the HONO gas through N sets of environments with different relative humidities to obtain N sets of HONO gases with different relative humidities, and to detect the sensitivity and background signal of the N sets of HONO gases with different relative humidities, respectively. Further, a chemical ionization system is used to detect the sensitivity and background signal of the HONO gas at different relative humidities.
Specifically, as shown in fig. 3, the sampling system comprises a main air inlet pipe (1), a particle separator (4), a bypass pipe (2) and an instrument sample inlet pipe (3), wherein the main air inlet pipe is connected with the bypass pipe and the instrument sample inlet pipe through the particle separator, and the instrument sample inlet pipe is connected with the chemical ionization system; after the gas enters the system from the main gas inlet, particles are separated through the main gas inlet pipe, aerosol particles in the gas are removed, and the aerosol particles are removed from the bypass port; and leading out the gas from which the sol particles are removed to a chemical ionization system through an instrument sample injection pipe for subsequent analysis.
Preferably, in the sampling system, the materials of the main air inlet pipe, the bypass pipe and the instrument air inlet pipe are selected from Teflon materials. The Teflon material preparation adopts a system, which is beneficial to sample collection and reduces pipeline interference.
Specifically, as shown in fig. 4, an ion source and a vacuum reaction chamber of the chemical ionization system. The ion source is connected with a vacuum reaction chamber, and the vacuum reaction chamber is connected with a 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 prepared by the georgia THS Instruments LLC study in the united states.
In some embodiments, in the chemical ionization system, an α -radiation source is adopted to quickly ionize to obtain iodide ions, and an environmental atmosphere sample to be tested reacts with the iodide ions, and the iodide ions have a strong electron affinity and react with HONO gas in the environmental atmosphere sample to be tested in an addition reaction of the following reaction formula: i - +HONO+M＝IHONO - +M, reaction to form IHONO - The method for detecting the polymeric ions can effectively and accurately observe the change of the gaseous nitrous acid in a short time due to rapid release of iodide ions, rapid reaction with a sample for measurement and rapid response time.
Preferably, the chemical ionization system comprises a vacuum reaction chamber, wherein the vacuum reaction chamber is made of 304 stainless steel, and the vacuum reaction chamber is cylindrical in shape. In some embodiments, the vacuum reaction chamber made of 304 stainless steel is selected for reaction, and as the 304 stainless steel has good corrosion resistance, heat resistance, low-temperature strength and mechanical properties, and good hot workability such as stamping, bending and the like, no heat treatment hardening phenomenon exists, the vacuum reaction chamber made of 304 stainless steel can improve the impurity doping free in the reaction process, and the reaction accuracy is improved; meanwhile, the reaction chamber is also ensured to be durable and can be reused. In other embodiments, the vacuum reaction chamber is cylindrical in shape, and a cylindrical reaction type is adopted, so that gas circulation is facilitated, response time is improved, contact between gas and a pipe wall is reduced, and reaction rate is ensured.
Further preferably, the length of the vacuum reaction chamber is 3 to 10cm and the inner diameter is 4 to 8cm. If the volume of the vacuum reaction chamber is too small, the reaction time is insufficient, and the reaction is incomplete; if the volume of the vacuum reaction chamber is too large, secondary reaction between the gas and iodide ions can be caused to form impurities, which affects the sensitivity of the detection result.
Specifically, as shown in fig. 5, 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 a vacuum reaction chamber of the chemical ionization system, 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.
In a preferred embodiment of the invention, the quadrupole mass spectrometry system is selected from quadrupole mass spectrometers. In some embodiments, the quadrupole mass spectrometer is selected from those prepared by the georgia THS Instruments LLC institute of america.
Preferably IHONO - When the mass spectrum detection is carried out on the polymer ions in the quadrupole mass spectrum reaction chamber, the mass-to-nuclear ratio of the polymer ions is 174, and IHONO can be detected under the condition that the mass-to-nuclear ratio is 174 - Mass spectrum signal intensity of the polymeric ions; i - When the mass spectrum detection is carried out on the ions, the mass-to-core ratio is 127, and the I can be obtained by detection under the condition that the mass-to-core ratio is 127 - Mass spectrum signal intensity of ions; IHCOOH (IH) - When the interference ion is detected by mass spectrum, the mass-to-core ratio is 173, and IHCOOH can be detected under the condition that the mass-to-core ratio is 173 - The mass spectrum signal intensity of the interference ions is directly output by the result processing module.
Further preferably, the concentration of gaseous nitrous acid in the ambient atmosphere is calculated from the sensitivity of the ambient atmosphere sample, the background signal of the ambient atmosphere sample, the mass spectrum signal intensity of the IHONO-polymeric ions, the mass spectrum signal intensity of the I-reagent ions, the background signal, the mass spectrum signal intensity of the IHCOOH-interfering ions, and the background signal.
The following is a further description of specific examples.
Example 1
Calibration curve of sensitivity and humidity, acquisition of calibration curve of background signal and humidity
The pressure of the vacuum reaction chamber is respectively set to be 24torr, 50torr, 62torr and 74torr; providing a HONO calibration system, generating HONO standard gas by using a HONO generator, and diluting the HONO standard gas through a zero-gas humidity adjusting system with adjustable humidity to obtain HONO gas with different relative humidity, wherein the HONO gas with different relative humidity comprises HONO gas with the relative humidity of 20% -80%, and when the pressure is 24torr, the HONO gas with different relative humidity is selected from 20% -80%; when the pressure is 50torr, HONO gases with different relative humidity are selected from 20% -60%; when the pressure is 62torr, HONO gases with different relative humidity are selected from 20% -70%; when the pressure is 74torr, the HONO gas with different relative humidity is selected from 20% -60%.
And detecting the sensitivity and the background signal of the HONO gas with different relative humidity under different pressure conditions by adopting a chemical ionization mass spectrometer.
Analysis of results:
analysis of a standard curve of HONO gas sensitivity plotted against N sets of different relative humidity and sensitivity, as shown in FIG. 6, when the pressure is 24torr, HONO gas of different relative humidity is detected, the equation of HONO gas sensitivity versus relative humidity is y=1.2E-6E -0.007x The method comprises the steps of carrying out a first treatment on the surface of the When the pressure is 50torr, HONO gas with different relative humidity is detected, and the equation of the sensitivity of the HONO gas and the relative humidity is y=5.1E-6E -0.022x The method comprises the steps of carrying out a first treatment on the surface of the When the pressure is 62torr, HONO gas with different relative humidity is detected, and the equation of the sensitivity of the HONO gas and the relative humidity is y=6.0E-6E -0.023x The method comprises the steps of carrying out a first treatment on the surface of the When the pressure is 74torr, HONO gas with different relative humidity is detected, and the equation of the sensitivity of the HONO gas and the relative humidity is y=7.0E-6E -0.024x 。
Analysis of a standard curve of the HONO gas background signal plotted against N sets of different relative humidity and background signal, as shown in FIG. 7, the HONO gas of different relative humidity was detected at a pressure of 62torr, and the equation relating HONO gas background signal to relative humidity was y=0.0043 e -0.023x 。
It follows that the sensitivity of the instrument to the measurement of HONO and the background signal decrease with increasing Relative Humidity (RH), and that the standard curve of HONO gas sensitivity is plotted as an exponential decay curve from N sets of different relative humidity and sensitivity and background signal. Since the pressure during the reaction will affect I at the same time - Reaction Rate with HONO and IHONO - And H is 2 The reaction rate of O, and therefore the sensitivity and background signal, is reduced with a decrease in gas pressure during the reaction.
Example 2
Measuring and analyzing the concentration of gaseous nitrous acid in the ambient atmosphere
12 months 2017, the concentration of gaseous nitrous acid in the environment atmosphere is measured and analyzed in Hebei Tangdu area
Providing a sampling system prepared from a Teflon material to collect an environmental atmosphere sample, enabling the environmental atmosphere sample to enter from an air inlet, removing impurities of the environmental atmosphere sample from a bypass port by adopting an air flow with the flow rate of 12-15 lpm through a collision cutter, and collecting the environmental atmosphere sample containing HONO from a main intersection by adopting an air flow with the flow rate of 1.5-2.5 lpm for measurement; measuring the relative humidity of an environmental atmosphere sample by adopting an external humidity detector, calculating the sensitivity of the environmental atmosphere sample by adopting the equation of the HONO gas sensitivity obtained in the embodiment 1, and calculating the background signal of the environmental atmosphere sample by adopting the equation of the HONO gas background signal obtained in the embodiment 1;
Controlling the pressure of an environmental atmosphere sample to be 62torr and the flow to be 1.5slpm in a chemical ionization mass spectrometer, wherein the molecular ion reaction formula is a cylinder made of 304 stainless steel material, the height is 5cm, and the inner diameter is 6cm; providing methyl iodide and nitrogen in a molecular ion reaction chamber, mixing to obtain methyl iodide/nitrogen steel cylinder gas, controlling the flow of the methyl iodide to be 5sccm and the concentration to be 3000ppm; mixing with nitrogen with the purity of more than or equal to 99.99% and the flow of 500sccm to obtain mixed gas; by using 210 The Po radioactive source carries out ionization treatment on the mixed gas to obtain iodine ions; reacting an environmental atmosphere sample with iodide ions to obtain a reactant;
IHONO in the reactant is measured by a quadrupole mass spectrometer - Mass spectrum signal intensity of polymeric ions, I - Ion, IHCOOH - The mass spectrum signal intensity of the interfering ions and the background signal, and the concentration of HONO is calculated,
analysis of results:
using quadrupole mass spectrometersSeparate measurement of IHONO in the reactants - Mass spectrum signal intensity of polymeric ions, I - Ion, IHCOOH - The mass spectrum signal intensity of the interfering ions, as shown in FIG. 8, can be clearly analyzed to obtain IHONO in the reactant - Mass spectrum signal intensity of polymeric ions, I - Ion, IHCOOH - The mass spectrum signal intensity of the interfering ions is calculated to obtain the concentration of HONO through the following formula,
wherein SIG 174/127 Is IHONO - Mass spectrum signal intensity of polymeric ions and I - Ratio of mass spectral signal intensities of ions; BKG Environmental atmosphere sample Calculating a background signal of an environmental atmosphere sample by adopting an equation of the HONO gas background signal; SIG (SIG) 173/127 For IHCOOH - Mass spectrum signal intensity of interfering ions and I - Ratio of mass spectral signal intensities of ions; BKG 173/127 For IHCOOH in mass spectrometry - Background Signal of interfering ion and I - A ratio of background signals of ions; SENS Environmental atmosphere sample Calculating to obtain the sensitivity of the environmental atmosphere sample by adopting an equation of HONO gas sensitivity; 1.2% (SIG) 173/127 -BKG 173/127 ) Is formic acid 13 The ratio of the C isotope signals.
Through calculation, the obtained concentration of the gaseous nitrous acid HONO in the environment atmosphere in the Hebei Wangdu area is 80-8200ppt.
Example 3
Test for interferents
By using the procedure of example 2 for measuring and analyzing the concentration of gaseous nitrous acid in the ambient atmosphere, NO was added to the sampling pipe 2 And HNO 3 The other operating steps were identical to those of example 2.
Analysis of results:
the test results are shown in Table 1 below, NO and HNO 3 The content of (2) is below the detection limit and cannot be detected and processed, so that the monitored HONO concentration is not affected at all. But only about 0.5% NO 2 Will be converted to HONO and have negligible effect on the measurement of HONO concentration.
TABLE 1
* U.D. indicates below the detection limit (30 ppt)
Example 4
High time resolution measurement and response time measurement
The HONO gas was introduced into the apparatus and its response time was tested.
Analysis of results:
as shown in FIG. 9, the HONO gas responds very rapidly in the device with a response time of less than 1s, while the HONO gas does not form an adhesion on the device and the inner wall of the sampling pipe, resulting in a hysteresis effect. Since the monitoring method does not require pretreatment of the sample, the chemical ionization reaction response is very rapid, and the sample is used as a detector by a mass spectrometer. So that the method can realize high time resolution monitoring and quick response of the HONO gas.
Comparative example 1
Measuring and analyzing gaseous nitrous acid concentration in ambient atmosphere by LOPAP instrument
12 months 2017, the concentration of gaseous nitrous acid in the environment atmosphere is measured and analyzed in Hebei Tangdu area
The concentration of gaseous nitrous acid in the ambient atmosphere was measured and analyzed in the region of Hebei sight in 2017, 12 months by using a LOPAP instrument, and the measurement result was compared with the measurement result of example 2.
Analysis of results:
as shown in FIG. 10, the measurement results of example 2 (CIMS) are substantially identical to those of comparative example 1 (LOPAP instrument) for HONO gas, the HONO concentrations measured by both instruments are substantially identical, R 2 Up to 0.9. The feasibility of the method was confirmed. The measurement method provided by the embodiment 2 of the invention has high accuracy, and the method provided by the embodiment 2 can be used for testing the HONO gas in the atmosphere.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and principles of the invention.
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.
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