液相氧化二次有机气溶胶生成机制及其对长三角雾霾生消与空气质量的影响

The causes responsible for the severe air pollution in China are quite complex, especially the formation mechanisms of secondary organic aerosol (SOA) are very poorly understood, in which the research regarding the aqueous-phase SOA (aqSOA) formation pathway is particularly very lacking. Since in the Yangtz River Delta (YRD) region, the atmosphere is often characterized with high relative humidity (RH), suggesting a likely more important role of aqSOA in the fine particles in this region than other regions. Therefore, in this proposal, we will systematically conduct the lab simulations, field measurements and air quality modeling, centering on the elucidation of aqSOA formation mechanism. The project will first carry out long-term on-line measurements and sample collections on the organic gas pollutants and fine particles in a few typical YRD areas, so as to unravel the major gas precursors that are likely significant for the aqSOA formation; then we will perform lab experiments to mimic the aqSOA formation process in the atmosphere for the most important precursors identified individually, elucidate the detailed mechanism, reaction parameters and characteristics of the aqSOA products by using a suite of advanced analytical techniques, and conduct in-depth analyses of the field data on the basis of the lab results, so as to understand the contribution, variation and evolution process of aqSOA in the ambient particles of this region; at last, we will combine the results of both laboratory and field studies, establish the aqSOA module and integrate it into the 3D air quality model, so as to evaluate accurately and systematically the influences of aqSOA on the evolution of haze and air quality in the YRD region. The research findings of this project will largely deepen our understanding on the key chemical processes which govern the complicated atmospheric pollution in China.

我国大气污染严重，成因复杂，对于二次有机气溶胶形成机制的认识还很不清楚，其中对液相氧化二次有机气溶胶（aqSOA）生成机制的研究尤为匮乏。鉴于长三角地区空气湿度偏高该机制可能较为重要，本项目立足长三角地区，系统开展围绕液相氧化机制的实验室模拟、外场观测以及空气质量模式研究。项目首先在长三角典型地区开展有机气体以及细粒子的长期在线观测和样品采集，分析确认区域内主要的aqSOA气态前体物；然后在实验室中对一些重要前体物的液相氧化过程进行详细模拟，综合多种分析手段，弄清其反应机理、反应参数及产物特征，并据此对细粒子外场数据进行深度解析，阐明区域内气溶胶中aqSOA的实际贡献及其演变规律；最后，通过整合aqSOA实验室模拟和外场观测成果，将aqSOA准确嵌入三维空气质量模型，评估其对长三角区域灰霾生消过程和空气质量的影响。项目研究成果将有助于深化对我国大气复合污染中关键化学过程的科学认知。

我国大气灰霾污染频发，PM2.5浓度偏高，其成因也较为复杂。其中学界对细粒子中二次有机气溶胶（SOA）生成反应机制认识尤为不清楚，而有关液相氧化生成的SOA（aqSOA）机制的研究尤为匮乏。鉴于长三角地区湿度较高，本项目立足长三角，系统开展围绕液相氧化机制的实验室模拟、外场观测以及空气质量模式研究。项目所取得的重要结果总结如下： 1）以高分辨率气溶胶质谱分析为核心，建立了aqSOA在线分析系统，全面研究了10种生物质燃烧排放前体物（苯酚，丁香酚，愈创木酚，间苯二酚，对苯二酚，甲氧对苯二酚，4-乙基苯酚，4-甲基丁香酚，丁子香酚，2,4,6-三甲基苯酚）的液相氧化过程，获得了前体物降解速率，SOA产率、元素组成及质谱，以及SOA单位质量吸光效率等参数，弄清了相关aqSOA生成机制；2）选取了萘醌，菲，二苯并噻吩等三种物质作为代表物，首次证实了中挥发性有机物作为aqSOA前体物的可能性和重要性，aqSOA有较高的产率，同时产物还具有吸光性（棕碳组分）。（3）通过对北京、南京上海等地大气细粒子质谱观测数据的深度解析，证实了aqSOA在冬季PM2.5污染有一定贡献（如南京冬季，aqSOA可占SOA总浓度的40%），aqSOA与湿度呈现明显正相关关系，在个别严重污染事件中贡献十分显著；但在春夏季（如南京地区春季）灰霾污染中，aqSOA作用不明显。（4）在SOA模拟方面，更新CMAQ-SAPRC11气相反应机理和SOA反应模块（尤其是异戊二烯生成产物IEPOX和MAE，以及乙二醛和甲基乙二醛的非均相反应生成机理），系统评估了非均相SOA对我国SOA生成的影响；还进一步考察了前体物极性及水汽吸收对SOA的影响；将实验室模拟得到的化学反应参数纳入CMAQ区域空气质量模拟中，并初步证实新的aqSOA机制的纳入，对于提高我国尤其是长三角地区SOA模拟的准确性有较好作用。本项目深化了对于aqSOA前体物类别、反应机制及产物理化特性的认识，相关研究成果也提高了对于我国大气复合污染中关键化学过程的科学认知，对于我国灰霾成因及其应对调控具有较好的科学意义。