京津冀及周边区域PM2.5叠加沙尘重污染过程特征及预报效果分析

Heavy Pollution Characteristics and Assessment of PM2.5 Predicted Model Results November 23 to December 4,2018

选取京津冀及周边区域2018年11月23日至12月4日一次大范围、长时间且PM2.5叠加两次沙尘传输的复合型重度污染过程开展特征研究,分析了首要污染物PM2.5和PM10浓度的发展演变,以及污染气象影响因素;结合激光雷达地基和车载走航监测结果,以及HYSPLIT后向轨迹结果,讨论了区域污染传输的情况;并对重污染期间NAQPMS、CMAQ和CAMx这3个空气质量模式的预报效果进行了回顾分析.结果表明,研究时段PM2.5叠加两次沙尘传输导致区域中南部多数城市达到重至严重污染水平,张家口、北京、石家庄、邯郸和郑州PM10小时峰值分别为1589、864、794、738和766μg·m^-3,PM2.5小时峰值浓度分别为239、319、387、321和380μg·m^-3.地面弱气压场、高湿、逆温等静稳条件和沙尘是重要的污染气象和天气因素.激光雷达地基和车载走航监测数据结合HYSPLIT后向轨迹分析表明重污染期间区域西南和东南方向发生了PM2.5传输;区域两次沙尘过程主要受西北路径传输影响.此外,NAQPMS、CMAQ和CAMx这3个模式均可较好地预测到京津冀及周边区域的重污染过程,但对个别城市预报略有偏差.该次重污染过程中模式对PM2.5的预报效果要好于PM10,这与气象模式预报、大气化学反应机制、污染源清单的不确定性,以及重污染应急措施导致的污染源排放的改变有一定关系.

This study discusses the concentration characteristics of PM2.5 and PM10,as well as pollution meteorology in large-scale and long-term heavy pollution in the Beijing-Tianjin-Hebei region and its surrounding areas from November 23 to December 4,2018,where the primary pollutants are comprised of PM2.5 and PM10.The monitoring results obtained from ground-based and vehicle-mounted lidars,as well as the HYSPLIT-4 backward trajectory combined with meteorological factors analysis are discussed.The accuracy and uncertainty of the air quality forecast model of NAQPMS,CMAQ,and CAMx during heavy air pollution were analyzed retrospectively.The results show that PM2.5 and sand dust in most cities in the south-central region contribute to severe pollution levels.The hourly peak concentrations of PM10 in Zhangjiakou,Beijing,Shijiazhuang,Handan,and Zhengzhou were 1589,864,794,738,and 766μg·m^-3,respectively.The respective hourly peak concentrations of PM2.5 were 239,319,387,321,and 380μg·m^-3.Ground static pressure field,high humidity,inversion,and other static and stable conditions,as well as sand dust transmitted from the northwest,were important pollution meteorological and weather factors.The monitoring data of ground-based lidar and vehicle-mounted lidar combined with the HYSPLIT-4 backward trajectory analysis showed that the air pollutant transmitted from the Southwest and Southeast during the heavy pollution period was primarily PM2.5.The air pollutant transmitted from the Northwest during the two sand dust processes.Moreover,the model of NAQPMS,CMAQ,and CAMx performed well in forecasting the heavy pollution process in the Beijing-Tianjin-Hebei region and its surrounding areas.However there are slight deviations for some individual cities,related to uncertainty in the meteorological model prediction,atmospheric chemical reaction mechanism,and pollution source list.Furthermore,the reduction in pollution source emissions caused by pollution emergency measures was also one of the main reasons for the overestimation.