基于环境大气的有机气溶胶挥发性及其演化研究

The volatility of organic aerosol (OA) determines gas-particle partitioning of organic compounds, and is a key property for investigating the formation and evolution, as well as the fate of OA in the atmosphere. Volatility quantified as volatility bin set data from OA can be applied directly to constrain the model simulation results. Whereas volatility of atmospheric OA contributed by different complex sources remains unclear. In a past study, the applicant showed the volatility of biogenic secondary organic aerosol is lower than values from traditional recognition. However, the evolution of OA volatility along with its long aging time has not been reported in published literatures. To answer these questions, field studies to explore the volatility of OA and its evolution is needed. In this project, we will conduct two ambient campaigns to examine the volatility of OA in typical polluted areas of China from several aspects. We will quantify the volatility bin set data of OA contributed by different sources based on the measurement with thermodenuder and aerosol mass spectrometer, combined with source apportionment model. Then we will evaluate the influences of kinetic parameters to the volatilization process of OA and distinguish the main controlling factors for OA volatility. By combining the field-deployed oxidation flow reactor (OFR) and OA volatility techniques described above, we can elucidate the volatility variation as a function of OA aging. The results of this project would provide theory basis for understanding the secondary formation and evolution of OA, and important parameters for OA model simulation. Eventually, the results can help policy making to control the air pollution of China.

有机气溶胶（OA）的挥发性决定有机物气固分配，是关系环境大气OA生成、演化和去除的关键化学特性，其量化表达直接约束OA模型模拟结果。然而我国环境大气OA来源众多，不同来源OA的挥发性量化特征仍不明确。申请人已发现环境大气生物源二次有机气溶胶的挥发性比传统认知更低。但在长时间大气老化过程中，OA挥发性如何演化，尚未有文献报道，急需观测结果回答。本项目针对以上问题，计划在我国典型污染区域开展OA的挥发性外场测量研究。基于热解析和质谱技术，结合动力学模型模拟获得对污染有主要贡献的不同来源OA挥发性的量化特征，评估相应关键动力学参数对挥发过程的影响，辨别影响挥发性的主要因素。结合外场老化实验与OA挥发性测量技术，阐明并参数化OA挥发性随不同老化时间的演变规律。通过本项目的研究，将为理解OA和PM2.5的二次生成和老化过程提供重要理论基础，为OA模型模拟提供参数支持，帮助我国大气污染治理政策的制定。

挥发性是有机气溶胶（OA）重要的物理化学特性，准确量化挥发性是解答大气 OA 形成、演化、去除及模型模拟的关键。然而，目前我国对于实际大气中不同来源 OA 挥发性的量化表征、影响因素及其参数模拟仍十分有限，如决定 OA 气固分配的蒸发焓和质量迁移系数具有较大不确定性。此外，不同来源 OA 在老化过程中挥发性演化也尚不清楚，增加了 OA 模型模拟的不确定性。本项目使用热解析管及气溶胶质谱仪在我国典型污染区域的四个站点进行了综合外场观测，获得不同人为源影响下OA的挥发性数据，并建立源开放的动力学模型定量OA挥发性分布及其关键动力学参数，研究还通过对比动力学模型同其他挥发性估计方法的结果，明确了不同挥发性估计方法之间的差异和可能原因，降低挥发性测量和估算的不确定性。四个观测站点结果显示环境OA的挥发性普遍低于实验室产生的OA，明确了实际大气环境OA的复杂性和老化的重要影响。四个站点中环境 OA 的焓变均为100 kJ mol-1，表明人为源影响地区OA相对于温度的敏感性相一致。而广州、北京城市站点观测地点获得的质量迁移系数（分别为0.7和1）明显高于另外两个城市下风向站点的0.1-0.5，表明城市站点中环境OA的动力学传质限制较小，这主要与城市地区一次排放源贡献较高有关，相关研究结果为模型模拟SOA提供了更为精确的数据基础和动力学模拟参数。本项目系统量化了中国城市地区3类常规一次源（机动车，生物质和餐饮源）和4类二次来源（按照氧化性分类）对OA的贡献及其挥发性分布，精确量化的不同来源OA挥发性分布为模型模拟提供关键输入和约束数据。最后, 本项目通过实际观测进一步探索了老化对 OA 挥发性的影响，通过总结不同观测站点不同来源OA 挥发性和外场流动管氧化实验，发现在气溶胶传输过程中，大气氧化作用明显增加OA的氧化程度，并降低其挥发性，增强了老化作用对有机气溶胶挥发性的认识。本项目阐明了我国颗粒物物种关键组分有机气溶胶的挥发性及其演化规律，相关结果为精细化控制PM2.5，并理解其大气环境效应提供了关键的科学依据。