Models-3/CMAQ modeling system was used to simulate the spatial and temporal distribution of PM2.5 pollution over Beijing during APEC, 2014(i.e. November 3 to 11, 2014). IPR, a process analysis tool embedded in CMAQ, was employed to quantify the contributions of different atmospheric processes to the PM2.5 formation at two typical sites (i.e. Guanyuan and Dingling) during two short-time pollution processes (i.e. Nov. 4 13:00 to Nov. 5 12:00 and Nov. 10 13:00 to Nov. 11 12:00). The results showed that CMAQ reproduced the temporal variation and magnitude of PM2.5 reasonably. Adverse synoptic system occurred on Nov. 4 and Nov. 10, resulting in two peak values of PM2.5 (188μg/m3 and 124μg/m3). Elevated PM2.5 levels didn't last long because of the pollution control measures and the cold anticyclone. During Nov. 4 13:00 to Nov. 5 12:00, horizontal transport was the primary contributor to the PM2.5 at both Guanyuan and Dingling, with a contribution rate of 49.6% and 90.9%, respectively, indicating that Beijing was mainly affected by pollution transported from southern areas. During Nov. 10 13:00 to Nov. 11 12:00, PM2.5 at Guanyuan site mainly came from local emission (78.8%), while PM2.5 at Dingling site mainly came from relatively weak horizontal transport, demonstrating a local pollution characteristic. Vertical transport played a dominative role in the decrease of PM2.5 in both pollution processes.

2014年2月19—27日,北京出现了重度污染及以上水平的霾天气,严重危害着人们的身体健康。以北京该段持续污染过程为研究对象,基于同期气象数据与PM_（2.5）观测数据,利用SPSS统计软件分析了PM_（2.5）浓度与气象因子间的相关性,探究区域周边城市PM_（2.5）污染变化特征及其与地面天气形势之间的关系。研究结果表明,在一定的气象条件下,PM_（2.5）浓度与风速、相对湿度分别呈显著的负相关、正相关,与气压呈负相关,与气温无显著相关关系。同时,比较该时段北京市与周边区域7个城市的PM_（2.5）浓度变化趋势及后向轨迹分析,发现北京市与周边城市在相似的气象背景条件下,污染过程具有区域性特征。华北地区处于地面高压均压场控制时,地面风速小,逆温层明显,大气层结稳定,区域扩散条件差,弱偏南气流主导时间长,受局地源积累和区域输送的影响,污染物浓度累积上升,可形成持续霾天气。

In January 2013, Beijing area experienced several severe haze weather events. The pollution of fine particles has become an important problem in Beijing. Understanding the sources of PM2.5 in Beijing is essential for solutions and related policy-formulations. Three-dimensional air quality modelling system was established to analyze the PM2.5 pollution during 20-24 January in 2013. PSAT technology was used to study the regional sources of Beijing PM2.5 pollution. The results showed that local emission was the major source of PM2.5 in Beijing City, with an average contribution rate of 34% . The average contribution rates of Hebei and Tianjin were 26% and 4%, respectively. The neighboring area and the boundary conditions contributed 12% and 24% to PM2.5 in Beijing. In the heavy pollution period, the influence of regional transportation increased significantly, and became the major source of PM2.5 pollution in Beijing. Nitrate in PM2.5 in Beijing mainly came from the surrounding area of Beijing City, while sulfate and secondary organic aerosols showed characteristics of long-distance transportation. Ammonium salt and other components were mainly from Beijing local contribution.