中文摘要：

为了研究北京冬季重污染过程的污染特征及形成原因,选取2013年1月915日一次典型重污染过程,对污染期间气象要素、大气颗粒物组分特征和天气背景场进行综合研究.结果表明,此次大气重污染过程中PM10和PM2.5平均质量浓度分别为347.7μg/m3和222.4μg/m3,均超过环境空气质量标准（GB3095-2012）中规定的日均二级浓度限值.重污染时段PM2.5中NH4＋、NO3-和SO42-质量浓度之和占PM2.5质量浓度的44.0%,OC/EC的平均比值为5.44,说明二次无机离子和有机物对此次污染过程中PM2.5贡献较大.稳定的大气环流背景场、高湿度低风速的地面气象条件和低而厚的逆温层导致北京地区大气层结稳定,加上北京三面环山的特殊地形结构,是造成此次大气重污染过程的主要原因.

英文摘要：

In order to study the characteristics and formation mechanism during a heavy air pollution episode in Beijing during 915January in 2013, the weather conditions, chemical characteristics of particulate matter and atmospheric environmental background were analyzed. The results showed that the average daily mass concentrations of PM10 and PM2.5 were 347.7μg/m3 and 222.4μg/m3, respectively, exceeding the corresponding ambient air quality standards（GB3095-2012） of China. During the pollution episode, NH4＋, NO3- and SO42- made a combined contribution of 44.0% to PM2.5 concentration. The average ratios of OC/EC were 5.44. This indicates a large contribution from secondary ions and organic matters to PM2.5. The atmosphere was relatively stable during the study period in Beijing because of the stable atmosphere circulation, the adverse near-ground meteorological conditions of high humidity and low wind speed as well as the lower and deeper inversion layer. The stable atmospheric condition and the land structure surrounded by mountains on three sides in Beijing restrained the dispersion of pollutants, and these were the main causes of this heavy pollution process.