自然排放与人为排放的相互作用对长三角地区二次有机气溶胶形成的影响机制研究

The Yangtze River Delta (YRD) has been experiencing severe fine particle (PM2.5) pollution in recent years. As an important component of PM2.5, secondary organic aerosol (SOA) is formed via the interactions of precursors emitted from biogenic and anthropogenic sources in this region. Thus, the chemical composition and distribution of fine particles are with significant regional characteristics. However, there were very few studies looking into the impacts of biogenic and anthropogenic interactions on SOA in the YRD region by far. This project will implement a newly developed air quality model CMAQ-MCM-SOA to simulate air pollution of fine particles in the YRD region, and investigate the contribution of biogenic VOCs (isoprene and monoterpenes) to the regional SOA. An advantage of the CMAQ-MCM-SOA model is the explicit treatment of multi-oxidation of 142 non-methane VOCs in the Master Chemical Mechanism (MCM), which enables to simulate the molecular composition of SOA. In addition, the model incorporates SOA from oxidation of BVOCs that could greatly improve modeled concentration. This project will analyze the spatial and temporal patterns of SOA and its chemical composition in the YRD region. The impacts of anthropogenic emissions, meteorological conditions, and long-range transport of pollutants on the regional SOA will be discussed as well. These results would enhance our understanding of chemical mechanism of aerosol, providing scientific support to the policy making in air pollution control in YRD.

长三角地区是细颗粒物(PM2.5)重污染区域，其中二次有机气溶胶(SOA)是PM2.5的重要组分。由于该地区SOA的前体物同时来自自然源排放和人为源排放，PM2.5的化学组成及分布具有特殊性，但目前对于这方面的研究存在很大的不足。本项目拟采用CMAQ-MCM-SOA模型模拟长三角地区细颗粒物的化学组分，深入探讨自然源排放与人为源排放相互作用机制及对该地区SOA的影响。该模型的优势是，利用复杂光化学机制Master Chemical Mechanism（MCM）可以从分子水平精确模拟SOA的化学组分，同时在传统CMAQ气溶胶模块的基础上加入了新发现的自然源有机物生成SOA的机制，更准确地描述SOA的浓度和化学性质。该项目拟从时空分布角度出发分析该地区SOA浓度和化学组分变化规律及主要影响因素。研究结果将加深对SOA化学演变过程的理解，为该地区雾霾防控政策的制定提供科学理论支撑。

长三角地区是细颗粒物(PM2.5)重污染区域，同时受自然源排放和人为源排放共同影响，二次污染物的形成机制具有区域特性。本项目采用CMAQ-MCM-SOA模型模拟长三角地区细颗粒物的化学组分，深入探讨自然源排放与人为源排放相互作用机制及对该地区SOA的影响。通过多机制比较发现，MCM机制模拟的大气氧化剂水平（自由基、臭氧）等显著高于SAPRC11机制，可以提高模型对臭氧峰值的低估，与观测符合更好。CMAQ-MCM-SOA模型模拟的烷烃、烯烃类有机物显著高于观测值，芳香烃则与观测符合较好。长三角地区夏季SOA显著高于冬季，且由自然源排放的污染物生成的BSOA占比高于人为源生成的SOA(ASOA)。在长三角高温高湿的环境下，水分子向有机相的分配促进SOA的形成，这一过程与BSOA密切相关，并显著提高气溶胶吸湿性、液态水含量、光学厚度等。增加温度、降低风速和降低边界层高度均显著增加SOA浓度。改变BVOCs排放与ASOA和BSOA变化均呈正相关，改变AVOCs排放显著影响ASOA形成，对BSOA形成影响不显著。增加NOx排放可显著提高BSOA浓度。