Xu Ran, Zhang Heng-de, Yang Xiao-Wen, Cheng Shui-Yuan, Zhang Tian-Hang, Jiang Qi
National Meteorological Center, Beijing 100081, China.
Key Laboratory of Beijing on Regional Air Pollution Control, College of Environmental and Energy Engineering, Beijing University of Technology, Beijing 100124, China.
Huan Jing Ke Xue. 2019 Aug 8;40(8):3405-3414. doi: 10.13227/j.hjkx.201806061.
To study the changing of characteristics and formation mechanisms of PM in Beijing during the last two years, particulate matter concentrations, weather conditions, and air-mass trajectories were analyzed during severe pollution episodes in fall and winter 2016-2017 using routine observations and the TrajStat model. Results showed that 13 heavy pollution events, each lasting at least two days, occurred in Beijing. Of these, approximately 61.5% occurred in winter, characterized by heavier pollution concentrations and longer durations than those occurring in autumn. A low-pressure gradient, high humidity, low surface wind speed, low boundary layer, and particular terrain (i. e., being surrounded by mountains on three sides) all contributed to the high occurrence frequency of severe pollution episodes in autumn and winter. During the pollution episodes, the average ratio of PM to PM reached 0.86. The air-masses during the accumulation stage were mainly transported from the northwest, west, southwest, and southeast of Beijing. The southwestern and southeastern transmission paths accounted for 21.6% of the total pollution load. In addition, the WRF-CAMx model was used to quantitatively analyze the contributions of local and external sources to the concentrations of PM in Beijing during 16-22 December 2016. Based on this analysis, PM contributions notably varied with different air-masses; in the case of southern air-masses, external sources dominated the PM concentrations in Beijing and local contributions decreased rapidly; in contrast, in the case of northwestern air-masses, the opposite pattern occurred. Overall, the contribution of local sources to PM concentrations in Beijing varied from 16.5% to 69.3% during the monitored pollution episodes.
为研究北京近两年来细颗粒物（PM）的特征变化及形成机制，利用常规观测数据和TrajStat模型，对2016 - 2017年秋冬严重污染时段的颗粒物浓度、气象条件和气团轨迹进行了分析。结果表明，北京共发生13次持续至少两天的重污染事件。其中，约61.5%发生在冬季，其污染浓度更高，持续时间比秋季的重污染事件更长。低压梯度、高湿度、低地表风速、低边界层以及特殊地形（即三面环山）均导致秋冬重污染事件高发。在污染时段，PM与PM的平均比值达到0.86。累积阶段的气团主要从北京的西北、西部、西南和东南部传输而来。西南和东南传输路径占污染总负荷量的21.6%。此外，利用WRF - CAMx模型定量分析了2016年12月16 - 22日北京本地和外源对PM浓度的贡献。基于该分析，PM的贡献随不同气团显著变化；在南风气团情况下，外源主导北京的PM浓度，本地贡献迅速降低；相反，在西北风气团情况下，情况则相反。总体而言，在监测的污染时段，北京本地源对PM浓度的贡献在16.5%至69.3%之间变化。
