2015年“十一”期间北京市大气重污染过程分析

采用垂直观测、地面观测、PM_2.5化学组分观测和气团轨迹分析等手段，对2015年10月份北京市一次大气重污染过程进行了分析.结果表明，重污染时近地面层气溶胶消光系数升高，污染物主要积聚在600m以下.重污染期间气象要素特征为：风场弱，湿度大，地面受弱气压场控制，边界层高度极低.重污染期间不同站点PM_2.5浓度变化趋势和峰值出现时间较为一致；大部分时段PM_2.5中NO₃^-浓度明显高于其他组分；周边区域受重污染的影响面积相对较小，高浓度区主要集中在北京市及近周边地区.多手段的观测结果以及PM_2.5浓度与气象要素和各化学组分的相关性分析的结果均表明：区域传输，包括秸秆焚烧，对本次北京市重污染天气过程具有一定的影响，但本地机动车排放在不利气象条件下的积累、二次转化以及垂直方向空间的极端压缩是导致重污染的主要原因.

Analysis on a heavy air pollution process in Beijing during National Day holiday, 2015

A heavy air pollution episode in Beijing in October 2015 was analyzed through vertical observation, ground-based observation, monitoring data of chemical components of PM_2.5 and back-trajectories of air mass. The results showed that aerosol extinction coefficient increased significantly during the episode, indicating that air pollutants accumulated within 600m height from ground. Comparing with normal days, wind speed was weaker, relative humidity was higher, surface pressure was lower and boundary layer height was lower during the episode. The variation and peak appearance were consistent among different monitoring sites, and NO₃^- concentration was higher than other components of PM_2.5 in most time. In addition, the surrounding region of North China Plain affected by heavy pollution was relatively small, while PM_2.5 accumulation in Beijing and its nearby region was more prominent. Multi-observations and correlation analysis between PM_2.5 and meteorological factors and chemical compositions showed that this episode was affected by regional transport to some extent, including straw burning. However, the accumulation and chemical reaction of local NO₂ emission under unfavorable meteorological conditions and extreme space compression in vertical direction was the main cause.