南京市两次秋季污染过程及成因分析

为探究南京秋季污染过程的特征和影响因素,利用MODIS(Moderate Resolution Imaging Spectroradiometer)传感器获得的气溶胶光学厚度(Aerosol Optical Depth)、波长指数(Angstrom Exponent)、火点数据及CALIPSO(Cloud-Aerosol Lidar And Infrared Pathfinder Satellite Observations)卫星数据和来自NECP、MICAPS的温度、相对湿度、风向风速等常规气象要素数据,对南京2015年10月、2016年9月两次污染过程进行分析.研究结果表明:两次污染过程的AE412-470值(埃斯特朗波长指数α)均高于1,由此判断两次污染均以人为排放产生的细粒子为主.但2015年10月的AE412-470值明显低于2016年9月,说明在2015年10月污染过程中粗粒子所占比重高于2016年9月.结合对后向轨迹的分析发现,南京地区2015年10月污染天气的发生还受长距离输送的影响,污染源主要为来自内蒙古、山西等地的污染型沙尘粒子.研究还发现,较高的相对湿度、较低的地表风速、低混合层高度及贴地逆温等气象条件会导致污染物难以扩散稀释而累积在南京地区,造成该区域在秋季出现较严重的污染天气.

Analysis the cause of two heavy air pollution events in autumn over Nanjing

This study investigates the characteristics and factors influencing the haze formation process during autumn (September-November) over Nanjing (China) during 2015-2016. For this purpose, the aerosol optical depth (AOD), fire points and Angstrom exponent (AE) data derived from Moderate-resolution imaging spectroradiometer (MODIS) and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) were used. The meteorological data derived from National Centers for Environmental Prediction (NCEP) comprised of temperature, relative humidity,wind speed and direction. The Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model was further used to examine to reconstruct the origins of air masses in this season. The high values (>1) of AE_412-470 during this season showed dominance of anthropogenic fine-mode particles. Analysis of aerosol subtypes derived from the CALIPSO and HYSPLIT revealed a clear indication of dust particles originated from Inner Mongolia and Shanxi contributed to the haze processes. The stagnant synoptic meteorological conditions (characterized by high relative humidity, low wind speed and low mixed layer height) made the pollutants difficult to disperse leading to severe pollution events in autumn over Nanjing.