CN-119534600-B - Quantitative method for trace gaseous nitrous acid generated by photolysis

Abstract

The invention discloses a method for quantifying trace gaseous nitrous acid generated by photolysis, which comprises two modes, wherein in the mode one, a chemical ionization mass spectrometer in a positive ion mode is used for quantifying the concentration change of Volatile Organic Compounds (VOC) which react with hydroxyl radicals (OH) after switching on a mercury lamp, so as to quantify the concentration of OH generated by irradiation of the mercury lamp, further Nitric Oxide (NO) reacts with OH to generate gaseous nitrous acid (HONO), and the generated concentration of HONO is approximately equal to the changed concentration of VOC measured by the mass spectrometer under the condition of excessive NO. Mode two uses the NO analyzer to measure the concentration change of NO reacting with OH before and after the mercury lamp is turned on to quantify HONO and OH, and the concentration of OH generated by the mercury lamp irradiation and the concentration of HONO generated under the condition are approximately equal to the NO concentration change measured by the NO analyzer.

Inventors

• HOU KEYONG
• Kong Jichuang
• CHEN SHUANG
• WANG LINSEN
• ZHOU QUAN

Assignees

• 山东大学
• 中国空气动力研究与发展中心设备设计与测试技术研究所

Dates

Publication Date

20260508

Application Date

20241129

Claims (8)

1. 1. A method for quantifying trace gaseous nitrous acid generated by photolysis is characterized by comprising the following steps: Introducing VOC gas with set humidity into a reaction flow tube, adopting a mercury lamp to photolyze water into OH, reacting the OH with VOC, adjusting the flow rate ratio of the VOC and the shading degree to ensure that the generated OH completely reacts with the VOC, wherein the initial concentration of the OH is the concentration of the consumed VOC; The VOC gas is replaced by NO gas, so that the concentration of the NO gas is larger than the initial concentration of OH, and the OH reacts with the NO to generate HONO; At this time, the concentration of gaseous nitrous acid produced is the initial concentration of OH; the ratio of the initial concentration of the introduced VOC to the initial concentration of OH is more than 1.5; The concentration of water vapor in the VOC gas is more than or equal to 50mg/m 3 ; the detection limit of the chemical ionization mass spectrometer is less than or equal to 0.5 ppbv.
2. 2. The method for quantifying a trace amount of gaseous nitrous acid generated by the electrolysis according to claim 1, wherein the VOC is alkane, aromatic hydrocarbon, alkene, halogenated hydrocarbon, ester, aldehyde or ketone.
3. 3. The method for quantifying a trace amount of gaseous nitrous acid generated by photolysis according to claim 1, wherein the VOC flow rate ratio and the degree of shading are adjusted so that the initial concentration of OH Less than the initial concentration of the incoming VOCs And can react fully.
4. 4. The method for quantifying trace amounts of gaseous nitrous acid produced by photolysis according to claim 1, wherein the VOC gas and the NO gas are provided by standard gas cylinders or standard gas generating methods.
5. 5. The method for quantifying the trace amounts of gaseous nitrous acid produced by photolysis according to claim 1, characterized in that it comprises the following steps: Introducing NO gas with set humidity into the flow reaction tube, and starting a mercury lamp for reaction; The generated concentration of HONO was quantitatively detected by detecting the decrease in NO measured by the NO analyzer before and after the mercury lamp was turned on.
6. 6. The method for quantifying the amount of trace gaseous nitrous acid generated by photolysis according to claim 5, characterized in that: 。
7. 7. The method for quantifying a trace amount of gaseous nitrous acid produced by hydrolysis according to claim 5, wherein the concentration of water vapor in the NO gas is not less than 50mg/m 3 .
8. 8. The method for quantifying the trace gaseous nitrous acid generated by the photolysis according to claim 5, wherein the detection limit of the nitric oxide analyzer is less than or equal to 0.5 ppbv.

Description

Quantitative method for trace gaseous nitrous acid generated by photolysis Technical Field The invention relates to the technical field of environmental quality monitoring, in particular to a quantitative method for trace gaseous nitrous acid generated by photolysis. Background Gaseous nitrous acid (HONO) is an important trace nitrogen-containing gaseous contaminant present in the atmospheric environment. In recent years, due to the progress of the atmospheric detection technology, the detection of trace gaseous nitrous acid in the atmosphere becomes possible, such as a long-path absorbance photometer, a differential optical absorption spectrometry, a mass spectrometry detection technology and the like, and the gaseous nitrous acid is taken as an important source of hydroxyl radicals (OH) in the atmosphere environment, is an important trace gas in the chemical circulation of the atmosphere, and in addition, nitrous acid and reaction products thereof have carcinogenic characteristics, so that researchers have carried out a great deal of research work, whether the reaction mechanism research of the gaseous nitrous acid in the atmosphere is carried out or the calibration of a gaseous nitrous acid measuring instrument is carried out, various researches are carried out by taking a simple and stable gaseous nitrous acid generating system as a standard source, and the photo-lysis generated HONO as the standard source of gas generation has a plurality of advantages, but the problem is how to accurately quantify the HONO generated by the standard source more accurately. The existing common methods for quantifying gaseous nitrous acid generated by photolysis include three, the first method is an improvement of the calibration method of the common chemical photometry HO x, wherein HONO is calculated according to the quantification values of [ O 3]、[H2 O ] and [ O 2 ] and the absorption cross sections of H 2 O and O 2 at 184.9nm, the second method is to thermally dissociate the HONO formed by the photolysis source and then quantify NO 2 generated by the generated thermal dissociation (Veres, etc., 2015), and the third method is mainly prepared in N 2([O2 ] =0.040%) and is simply quantified by measuring NO 2 formed by the reaction of NO with HO 2 generated by the photolysis of H 2 O. The third method has lower uncertainty (typically 10%,2σ) than the former two. The problems of the existing quantitative method for producing nitrous acid by photolysis are that the first method needs to characterize the emission spectrum of the mercury lamp, the work is complex, the second method and the third method indirectly quantify the generated HONO by measuring NO 2, and even though the third method has lower uncertainty compared with the second method, the two methods still have great improvement space due to the fact that the reaction is relatively complex due to the existence of O 2. Disclosure of Invention Aiming at the problems in the prior art, the invention provides a method for quantifying trace gaseous nitrous acid generated by photolysis, which is simpler and more convenient than the prior method, involves fewer side reactions and means lower uncertainty. In order to solve the technical problems, the technical scheme of the invention is as follows: in a first aspect, the present invention provides a method for quantifying trace amounts of gaseous nitrous acid produced by photolysis, comprising the steps of: Introducing VOC gas with set humidity into a reaction flow tube, adopting a mercury lamp to photolyze water into OH, reacting the OH with VOC, adjusting the flow rate ratio of the VOC and the shading degree to ensure that the generated OH completely reacts with the VOC, wherein the initial concentration of the OH is the concentration of the consumed VOC; The VOC gas is replaced by NO gas, so that the concentration of the NO gas is larger than the initial concentration of OH, and the OH reacts with the NO to generate HONO; at this time, the concentration of gaseous nitrous acid produced was the initial concentration of OH. The reaction mechanism is as follows: [OH]0≈△[VOC]＝[VOC]0-[VOC]。 In some embodiments, the VOC is alkanes, aromatic hydrocarbons, alkenes, halogenated hydrocarbons, esters, aldehydes, or ketones. Wherein, the alkanes such as methane, ethane, etc., the aromatic hydrocarbons such as benzene, toluene, xylene, etc., the olefins such as ethylene, propylene, etc., the halogenated hydrocarbons such as chloroethylene, bromoethylene, etc. The VOC can react rapidly with hydroxyl radicals and can be quantitatively detected by a chemical ionization mass spectrometer. The mercury lamp can generate hydroxyl radicals by irradiating water vapor. In some embodiments, the concentration of water vapor in the VOC gas is greater than or equal to 50mg/m 3. In some embodiments, the VOC flow ratio and shade are adjusted so that the initial concentration of OH [. OH ] 0 is less than the initial concentration of the incoming VOC