Miao Yucong, Liu Shuhua, Huang Shunxiang
State Key Laboratory of Severe Weather & Key Laboratory of Atmospheric Chemistry of CMA, Chinese Academy of Meteorological Sciences, Beijing 100081, China.
Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing 100871, China.
Sci Total Environ. 2019 Sep 10;682:464-474. doi: 10.1016/j.scitotenv.2019.05.199. Epub 2019 May 16.
The day-to-day variations in the planetary boundary layer (PBL) structure and air quality are closely governed by large-scale synoptic forcings. Partly due to the lack of long-term PBL observations during the winter in Beijing, the complex relationships between the large-scale synoptic patterns, local PBL structures/processes, and PM pollution have not been fully understood. Thus, this study systematically investigated these linkages by combining aerosol measurements, surface meteorological observations, radiosonde data, reanalysis, long-term three-dimensional meteorological simulations, and idealized meteorology-chemistry coupled simulations. Based on the validated long-term simulation results, the boundary layer height (BLH) in Beijing during two winters from 2013 to 2015 was calculated and compared with PM measurements. A significant anti-correlation was found between the daily BLH and PM concentration in Beijing, indicating the importance of the PBL structure on the variations in the aerosol pollution levels. Those days with low BLHs are often accompanied by a strong elevated thermal inversion layer. Based on the daily 900-hPa geopotential height fields, seven synoptic patterns were identified using an objective approach, in which two types were found to be associated with heavy PM pollution in Beijing. One pattern was characterized by weak northwesterly prevailing winds and a strong elevated thermal inversion layer over Beijing, and the local emissions of aerosols played a decisive role in the formation of heavy pollution. The other pattern was associated with southerly prevailing winds, which could transport the pollutants emitted from southern cities to Beijing. According to the meteorology-chemistry coupled simulations, southerly regional transportation can contribute approximately 56% of the PM in Beijing. The results of this study have important implications for understanding the crucial roles that multiscale meteorological factors play in modulating the aerosol pollution in Beijing during the winter.
行星边界层（PBL）结构和空气质量的逐日变化受到大尺度天气强迫的密切控制。部分由于北京冬季缺乏长期的PBL观测数据，大尺度天气形势、当地PBL结构/过程与PM污染之间的复杂关系尚未得到充分理解。因此，本研究通过结合气溶胶测量、地面气象观测、探空数据、再分析、长期三维气象模拟以及理想化的气象-化学耦合模拟，系统地研究了这些联系。基于经过验证的长期模拟结果，计算了2013年至2015年两个冬季北京的边界层高度（BLH），并与PM测量值进行了比较。发现北京每日的BLH与PM浓度之间存在显著的反相关关系，表明PBL结构对气溶胶污染水平变化的重要性。BLH较低的日子通常伴随着强烈的高空逆温层。基于每日900百帕等压面高度场，采用客观方法识别出七种天气形势，其中发现两种类型与北京的重PM污染有关。一种形势的特征是北京上空盛行弱西北风且存在强烈的高空逆温层，气溶胶的本地排放对重污染的形成起决定性作用。另一种形势与盛行南风有关，南风可将南方城市排放的污染物输送至北京。根据气象-化学耦合模拟，南风的区域输送对北京PM的贡献约为56%。本研究结果对于理解多尺度气象因素在调节北京冬季气溶胶污染中所起的关键作用具有重要意义。
