活性含氮痕量气体区域循环演化及大气二次污染物生成

PM2.5 and ozone are two vital regional air quality headaches in China, and control of nitrogen oxides (NOx) and ammonia (NH3) are becoming increasingly important to combat the air pollution problems. The present project is targeted on the atmospheric trace reactive nitrogen in the Pearl River Delta region. It aims to monitor atmospheric chemical evolution of NOx, NH3 and their gas- and particle-phase reaction products at representative urban, rural and forest stations by online techniques including the Thermal Dissociation-Laser Induced Fluorescence (TD-LIF), High Resolution-Time of Flight-Aerosol Mass Spectrometer (HR-ToF-AMS), and Proton Transfer Reaction-Time of Flight-Mass Spectrometer (PTR-ToF-MS); to deeply characterize chemical compositions of primary and secondary organic nitrogen species by offline analysis using tools like LTQ-Orbitrap; to measure ecosystem-atmosphere exchange fluxes of trace nitrogen species by eddy covariance technique and wet/dry deposition of inorganic and organic nitrogen as well; to study the formation and evolution dynamics of inorganic and organic nitrogen compounds by smog chamber simulation with representative combinations of air pollutants; to improve and validate the performance of air quality models with mechanisms from chamber study and data from field observations, and hereby conduct scenario analysis for future control of NOx and NH3 in the Pearl River Delta region. The study works in this project would not only help deeply understand regional cycling and evolution of organic nitrogen and trace nitrogen gases, but also provide solid support for designing unerring emission control measures to improve regional air quality.

PM2.5和臭氧是我国当前最突出的区域大气环境质量难题，氮氧化物（NOx）和氨气（NH3）管控的重要性日益凸显。本申请以珠江三角洲为研究区域，拟利用TD-LIF、HR-ToF-AMS、PTR-ToF-MS等在线分析手段，在典型城区、农村和森林站点观测NOx和NH3及其气相和颗粒相反应产物的大气演化特征；利用轨道阱（Orbitrap）质谱等离线分析手段，对大气一次和二次有机氮进行深度分析表征；在典型自然生态系统利用涡度相关等方法测量含氮痕量气体的地气交换通量，同时观测无机氮和有机氮干湿沉降通量；选取代表性体系进行烟雾箱模拟，揭示大气无机和有机氮生成演变的动力学机制；利用烟雾箱模拟获得的机制参数和外场观测数据改进和校验区域大气环境质量模式，并针对NOx和NH3管控进行大气环境影响的情景分析。项目研究可拓展对大气含氮痕量气体区域循环演化的科学认识，为区域大气环境质量改善的精准控制决策提供支撑。

氮氧化物（NOx）和氨气（NH3）等活性氮在PM2.5和臭氧（O3）污染形成过程中扮演着十分重要的角色。为深入探究活性氮的区域循环及大气演化，项目在建立气态和颗粒态活性氮分析方法基础上，开展了典型源活性氮表征、大气活性氮来源贡献、活性氮干湿沉降通量、典型站点大气活性氮观测、活性氮大气演化与生消过程烟雾箱模拟、含氮痕量气体区域循环演化模式模拟等方面的研究工作。主要成果包括：（1）建立了NH3、氧化亚氮、亚硝酸、NOx、硝酸酯、过氧硝酸酯等气态活性氮在线测量平台，利用气相色谱-质谱（化学电离源）对颗粒物中的重要含氮有机化合物组分进行了定量分析；（2）获得了典型源（机动车尾气和生物质燃烧等）的NOx、NH3等活性氮排放因子，评估了在我国近年来污染管控措施对NOx和NH3减排的效果。（3）连续3年实测了珠三角城市群地区重要大气活性氮（特别是有机氮）的干湿沉降水平以及其主要影响因素。（4）通过在珠三角典型站点的重要活性氮观测，厘清了城市群地区活性氮物种的时空特征和生消过程，定量解析了PM2.5中有机氮的来源。（5）基于烟雾箱模拟，探究了典型前体物和典型源在光反应和暗反应过程中的活性氮的演化机理，明确了活性氮组分在生成O3和二次气溶胶过程中的关键角色。（6）利用数值模拟，定量评估了人为排放源变化、气象条件变化和天气形势等对大气氮沉降的影响，构建了“标准差椭圆”法用于定量表征大气氮从排放到沉降过程中大气传输特点，并对重点区域传输过程进行了定量表征。本项目研究结果深化和拓展了对大气含氮痕量气体区域循环演化的科学认识，在机理和观测数据方面为相关模式的验证与改进提供支持，并为区域PM2.5和O3污染协同防控提供科学支撑。