海盐气溶胶对沿海城市大气颗粒物及组成粒径分布的调控机制研究

Sea-salt aerosol (SSA) is a major source of the atmospheric particles in cosatal urban areas.SSA can react with acid species such as HNO3,H2SO4 in the urban atmosphere and result in the increase of atmospherie particle concentrations and the change of their size distributions. The influence of SSA on the size distribution of particles would become more complicated when the level of SO2 decreases while NO2 level increases at the same time in the coastal urban atmosphere. As a result, the abatement effect of SO2 will become more difficult to be evaluated accurately. In this project, a local SSA emission module will be established based on the measurement and chamber results and will be used to update the emission inventory set up previously. Meteorological model (MM5) and air quality model (CMAQ) are used to model the particle size distribution in Taiwan straits, onshore monitoring sites, coastal urban sites and inland mountainous sites. The modeling results should be assessed with compared to the measurement results using MOUDI sampler at the sites mentioned above. The scenario analysis method is used to discuss the influence of SSA on the size distribution of atomspheric particles. In the end, the possibility of air quality improving will be assessed using CMAQ and the influence of SSA will be discussed.

海盐气溶胶（SSA）是沿海城市大气颗粒物的主要来源之一，可与城市大气中的HNO3等酸性组分发生反应，不仅会增加大气颗粒物的浓度，同时也会改变其粒径分布。当大气SO2浓度逐步降低而NO2持续增大时，SSA的输入对大气颗粒物及组成粒径分布的影响将变得更加复杂也更为显著，进而影响大气污染物减排效应的准确评估。本研究拟以受季风影响明显的福建沿海城市为研究区域，通过实测和模拟得到本地化的SSA排放模型，更新已有的大气污染物排放清单；再结合MM5气象场与CMAQ空气质量模型，模拟大气颗粒物及组成的粒径分布，并与出海航次、临海观测站、滨海城区与内陆山区的MOUDI实测数据进行比较、验证；在本地化CMAQ模型建立的基础上，通过在排放清单中纳入或忽略SSA，探讨SSA对沿海城市大气颗粒物及组成粒径分布的影响，并结合国家和地方大气污染物减排规划，对沿海城市达到空气质量改善目标的可能性进行评估。

基于福建省环境统计数据，再结合统计年鉴、社会经济发展等调研资料，采用排放系数法建立了福建省人为源大气污染物排放清单；天然源排放清单包括陆地植被排放VOCs和海洋排放海洋气溶胶(破波带+开阔海域)。破波带海盐排放模型与颗粒数浓度实测结果吻合，而开阔海域海盐排放模拟与MOUDI测量的质量浓度接近。搭建了WRF模型，初步分析厦门湾流场受地形和海陆风影响明显；排放清单初步应用于福建省环境监测中心站空气质量模拟平台。根据沿海城市及台湾海峡长期监测，确定沿海城市大气PM2.5的主要来源（汽车尾气）以及船舶排污的影响，发现海盐对大气颗粒态无机氮的沉降贡献占比为20.33%（沿海城市）和36.91%（开阔海域）。建立了大气NH3的被动采样与分析方法，确定其对大气氮沉降的贡献接近3成，且城市区域非农业源氨的贡献占主。建立了氮稳定同位素分析方法，计划后续研究中用于分析HNO3与海盐颗粒之间的非均相化学反应过程。