大气烷基硝酸酯的实地测量

Field Measurement of Alkyl Nitrates in the Atmosphere

烷基硝酸酯(ANs)是对流层大气中重要的污染物,其收支过程对大气氮、碳的分布,光化学循环以及二次有机气溶胶生成等具有重要影响.大气ANs种类繁多,浓度低且化学性质活泼,因此ANs的准确测量是大气监测领域的巨大挑战.概述了大气ANs化学机理,系统梳理并总结了ANs单物种和总量的实地测量技术进展,主要包括气相色谱电子捕获技术、质谱技术、荧光光谱技术和吸收光谱技术.研究表明吸收光谱技术具有结构简单易维护的特征,是具有较大发展潜力的ANs总量测量方法,质谱技术在ANs分物种测量方面具有其独特优势,但物种化的标准源和标定技术是亟待突破的关键瓶颈.最后,系统归纳了不同环境类型的ANs浓度分布特征,并对ANs化学研究难点和发展趋势进行展望.

Alkyl nitrates (ANs), chemicals with the formula RONO_(2), are important oxidation products during the reaction between atmospheric nitrogen oxides (NOx) and volatile organic compounds (VOCs). The generation of ANs removes NOx from the atmosphere, and inhibits atmospheric oxidation by terminating the HOx cycle. Some ANs are easily taken up by particulate, as important precursors of secondary organic aerosols, thereby affecting atmospheric air quality and global climate change. Atmospheric model simulations and field campaigns have shown that ANs are important for local complex pollution and nitrogen cycling. However, as ANs are widely distributed in the atmosphere, with a wide variety and active chemical properties, it makes the field measurements of ANs very scarce due to the lack of measurement methods and standard substances. In this study, firstly, the atmospheric chemical mechanism focused on ANs is introduced, and then the measurement techniques for single species and total ANs are summarized, which mainly include gas chromatography electron capture (GC-ECD), mass spectrometry (MS), thermal dissociation laser-induced fluorescence (TD-LIF) and absorption spectrometry. Overall, mass spectrometry is an important development direction for single-species measurement methods of ANs, while absorption spectroscopy is an emerging total measurement method with great development potential. Field measurements of ANs were carried out mainly in Europe and the United States. However, the atmospheric environment of high NOx and high anthropogenic VOCs in China is different from that of low NOx and high biogenic VOCs in Europe and the United States, and thus there are differences in the atmospheric distributions of ANs, which introduces challenge for field measurements of ANs. Finally, the distribution characteristics of ANs in the environments of ocean, forest, city, and free atmosphere in the troposphere are summarized, and an outlook on the difficulties and development trends of ANs chemistry at present is given, which will provide a reference for the development of the measurement technology and the research on the chemical mechanism of ANs in China.