有机示踪物气固相分配对有机气溶胶受体模型源解析的影响研究

Organic tracers in ambient particles are strongly associated with specific source classes, and are commonly used in receptor models for source apportionment of organic aerosols. The resulting source contributions could help in developing effective regulatory strategies to reduce aerosol emission and the evaluation of the health effects of individual sources. However, most organic tracers are semi-volatile and their particle-phase concentrations are strongly impacted by gas/particle (G/P) partitioning. Most G/P portioning measurement studies have focused on non- or semi-polar organic tracers, and very few field measurements have been conducted on the G/P partitioning of polar secondary organic tracers. As such, the source apportionment results might not reasonably reflect source contributions if only particle-phase concentrations of organic tracers were included in receptor models. In this study, the G/P partitioning of organic tracers will be measured and simulated, so as to understand the G/P partitioning mechanisms of difference organic tracers, especially the secondary organic tracers. In addition, the PMF model will be used to analyze particle-phase and total (gas + particle phase) concentrations of organic tracers, respectively. The results will be used to understand the influence of G/P partitioning on source apportionment of organic aerosols.

气溶胶中的有机示踪物具有较高的源指示性，常被用于有机气溶胶的受体模型源解析。源解析结果可为科学减排和各污染源的健康效应评估提供理论依据。然而大部分有机示踪物为半挥发性，其颗粒态浓度受气固相分配影响。目前，有机示踪物气固相分配的观测研究主要集中在非 (或弱) 极性化合物上，极性二次有机示踪物气固相分配的观测研究还比较少。因此仅利用颗粒态有机示踪物浓度进行源解析，获得的结果不能合理反映污染源贡献。本项目拟结合有机示踪物气固相分配的观测和模拟，理解不同有机示踪物的气固相分配机制，特别是二次有机示踪物。再利用受体模型 PMF分别对颗粒态示踪物浓度和示踪物总浓度(气态 + 颗粒态) 进行分析，系统了解气固相分配对有机气溶胶源解析的影响。

由于有机气溶胶的来源没有特定的金属元素组成特征，有机示踪物组成数据常被作为受体模型的输入信息解析其来源。大多有机示踪物为半挥发性，气固分配过程受许多因素如气温、相对湿度和颗粒态有机质浓度等影响。二次有机气溶胶浓度的模拟预测和基于有机示踪物组成的源解析研究均需要考虑气固相分配过程。为了探索主导有机示踪物气固分配过程的内在机制，消除气固分配对有机气溶胶源解析的影响，本项目在南京北郊一采样点同时收集不同极性有机示踪物的气态和颗粒态样品（PM2.5），收集过程中采用双滤膜采样评估因气态物质吸附造成的采样偏差；采用气质联用技术分析气态和PM2.5中正构烷烃、多环芳烃、含氧多环芳烃、霍烷和甾烷、异戊二烯二次产物和左旋葡聚糖等示踪物的质量浓度；跟据PM2.5中有机碳的质量浓度利用经验公式计算各有机示踪物吸收气固分配系数的测量值，并且同基于吸附平衡分配理论计算出的预测值进行比较。研究结果表明，颗粒态非极性有机示踪物浓度占总浓度百分比和物质的蒸气压呈负相关，而极性组分浓度在气固两相的分配受蒸气压影响较小。颗粒态有机示踪物挥发造成的采样偏差不可忽略，特别是对高分子量示踪物。吸收平衡分配理论可模拟非极性组分气固分配系数的时间变化趋势，但模拟结果的准确性有待提高。极性组分气固分配系数的观测值比模拟值高2-3个数量级，且二者之间无显著相关性，可解释为颗粒物中含有的大量液态水使得极性组分的气固分配不符合吸收平衡分配理论。通过对比基于示踪物总浓度和颗粒态数据的源解析结果，提出需要将气态和颗粒态总浓度作为输入数据对有机气溶胶进行源解析，避免因气固分配影响造成错误的源解析结果。这些研究结果除了有利于空气质量模式中二次有机气溶胶的模拟外，还将极大改进大气有机气溶胶的受体模型源解析工作。