2015年1月下旬北京市大气污染过程成因分析

采用地面观测和数值模拟相结合的方式，对2015年1月下旬北京市两次PM_2.5污染过程进行分析。研究表明，在第1次过程中PM_2.5浓度经过3个抬升阶段达到峰值，过程前期区域传输的作用明显，随后区域传输和本地污染积累、化学反应共同加重了污染的程度；3个浓度抬升阶段中均出现过PM_2.5浓度“跃升式”增长，且污染水平越重，浓度跃升的幅度越大。第2次过程是一次典型的静风、高湿度下的PM_2.5持续性增长过程，主要是本地污染物积累和发生化学反应二次生成导致的。大气氧化性分析和SOR、NOR分析均验证了对两次污染过程特征和成因的推断。数值模拟结果表明，第1次污染过程中区域传输对不同站点PM_2.5的贡献率在15.2%~68.7%之间；第2次过程区域传输的贡献率在12.8%~46.3%之间。

Formation mechanism of air pollution episodes in Beijing in late January 2015

Two PM_2.5 pollution episodes in Beijing in late January 2015 were analyzed through ground-based observation and numerical simulation. The results showed that concentrations of PM_2.5 reached a peak after three stages of increasing concentration in the first pollution episode. Regional transport had a significant impact on PM_2.5 in Beijing in the early stage of this episode. Subsequently, regional transport and accumulation, as well as chemical reaction of local pollutant emissions, aggravated this pollution episode. A surge in PM_2.5 concentrations occurred in all three stages of increasing concentration, and the surge was more significant when the PM_2.5 concentration was higher. The second pollution episode was a typical continuous increase of PM_2.5 concentrations in calm wind and high humidity conditions, which was mainly caused by the accumulation of local pollutant emissions and the occurrence of chemical reactions. This was verified by the analysis of O_x, SOR, and NOR. The results of the numerical simulation showed that regional transport contributed to 15.2%~68.7% of PM_2.5 at four sites during the first pollution episode, and 12.8%~46.3% during the second pollution episode.