利用氮氧同位素组成辨识汽车尾气来源的城市气溶胶硝酸盐

In China, vehicle exhaust has become the important source of urban air pollution, which is also the major cause of haze weather. Although it was recognized that NOx in vehicle exhaust is the important precursor of secondary aerosol nitrate, lack of effective tracing on the conversion process restricts the quantization study on its contribution. This project will choose the Tianjin City (serious pollution of vehicle exhaust) as example, and conduct a systematic study on the percent contribution of NOx to urban aerosol nitrate. By means of sampling gaseous NOx and aerosol particulate matter at city center and background site respectively, we analyze the concentrations and isotopic compositions of NOx and aerosol nitrate in collected samples. Based on the difference of above data among winter-summer, day-night, rush hour traffic-non rush hour traffic, and between city center and background site, contribution of vehicle exhaust NOx to urban aerosol nitrate will be quantified according to mixing model of isotopic compositions, and the process and atmospheric chemical reaction mechanism for NOx being converted into nitrate will be revealed simultaneously. The research achievements of this project will provide essential data and technological methods for quantifying the effect of vehicle exhaust NOx on urban fine particulate matter, and provide theoretical support for controlling NOx emissions and treating pollution aspects of urban aerosol nitrate.

汽车尾气已成为我国城区空气污染的重要来源，是造成灰霾天气的重要原因。尽管已经认识到汽车尾气氮氧化物是二次气溶胶颗粒物硝酸盐的重要前体，但由于缺乏对转化过程的有效示踪，限制了对其贡献的量化研究。本申请拟选取汽车尾气污染严重的京津冀地区特大城市-天津市为例，系统开展汽车尾气NOx对城市气溶胶硝酸盐贡献率的研究。通过在城区和上风向背景点分别采集气态NOx和气溶胶颗粒物样品，分析测定NOx和气溶胶硝酸盐浓度及其氮氧同位素组成，在比较季节、昼夜和交通高峰期时段差异以及城区和背景点差异的基础上，结合同位素组成混合计算模型，定量探究汽车尾气NOx对城市气溶胶硝酸盐的贡献，同时揭示NOx转化形成硝酸盐的过程及其大气化学反应控制机理。本申请项目的成果产出，将为量化汽车尾气对城市气溶胶细颗粒物的影响提供基础数据和技术手段，为控制并削减NOx排放、有效应对城市气溶胶硝酸盐污染问题提供理论支撑。

汽车尾气已成为我国城区空气污染的重要来源，是造成灰霾天气的重要原因。尽管已经认识到汽车尾气NOx是二次气溶胶颗粒物硝酸盐的重要前体，但由于缺乏对转化过程的有效示踪，限制了对其贡献的量化研究。本研究以京津冀地区特大城市-天津市为例，以统一的采样和测试方法首先建立了该地区6种NOx源的氮同位素组成特征谱；随后研究对比了2018/2019年度5个不同季节时段天津PM2.5中硝酸盐浓度及其稳定氮、氧同位素组成变化，并分析了其主要的受控因素；最后，基于贝叶斯同位素混合模型，输入建立的天津地区NOx源的氮同位素组成特征谱和观测数据，对NOx来源和硝酸盐的生成路径的贡献占比进行了精细量化，揭示了汽车尾气NOx并非总是硝酸盐的主要来源。研究的成果产出，为量化汽车尾气对城市气溶胶细颗粒物的影响提供了基础数据和技术手段，为控制并削减NOx排放、有效应对城市气溶胶硝酸盐污染问题提供了理论支撑。