2019年西安末场雾霾PM_(2.5)生消扩散特征

The characters of formation and diffusion of PM_(2.5)during the last fog⁃haze process in Xi′an in 2019

为了探寻西安雾霾气溶胶典型生消扩散特征,对2019年最后一场雾霾(简称末场雾霾)开展了高分辨WRF⁃Chem(the Weather Research and Forecasting model coupled to Chemistry)模拟,并结合环境监测站监测数据、以及特殊观测数据(西安理工大学气象站、粒谱仪、太阳光度计观测等),对末场雾霾发生发展的气象条件与气溶胶条件进行了综合诊断,研究结果如下:①通过与观测数据对比表明,模式较好地再现了雾霾生命史(发生于12月20—25日,于23日上午发展为重度霾).②四川北部是此次雾霾的发源地,在雾霾形成初期,沿着低矮地势存在一条输送通道(青川县⁃康县⁃徽县⁃两当县⁃秦岭西部低矮地形与青藏高原东部山脉之间的豁口⁃宝鸡⁃西安).③特殊的地形使得西安易于滋养雾霾,而较大尺度的秦岭山脉并不能完全阻挡西安雾霾的形成与扩散.④通过对比2019年首、末两场雾霾,揭示了两场雾霾气溶胶的共性特征:雾霾天气背景下,PM_(2.5)的组份以有机碳为主(接近或突破40μg·kg^(-1));偏北风是西安雾霾消散的关键因子(底层持续6 m·s^(-1)以上的平均风速,即可以吹散雾霾),雾霾消散时先从底层开始消散.

In order to discover the typical characters of formation and diffusion of aerosols during the fog⁃haze days in Xi′an,a high resolution numerical simulation on a fog⁃haze episode occurred in Xi′an in late December 2019(named as“the Last Fog⁃haze Process”)was carried out by using the WRF⁃Chem model(the Weather Research and Forecasting model coupled to Chemistry).Based on the multi⁃source dataset including the model data,the Chinese environmental station observation data,and the special observation data(the weather station,the particle size spectrometer,the Sun photometer)collected from Xi′an University of Technology(XUT),both the meteorological parameters and aerosol parameters during the Last Fog⁃haze Process were fully diagnosed,and the results were as follows.①With a heavy⁃haze phase on 23 December,the life cycle of fog⁃haze and PM_(2.5)(20—25 December 2019)were successfully reproduced by WRF⁃Chem according to both qualitative and quantitative test.②North Sichuan basin was the birthplace of aerosols during the Last Fog⁃haze,and a transport channel during the formation period was discovered(Qingchuan⁃Kang⁃Hui⁃Liangdang⁃Low terrain between West Qinling and East Tibetan Plateau⁃Baoji⁃Xi′an).③The terrain surrounding Xi′an was favorable for the formation and development of fog⁃haze,and aerosols could transmit along the low terrains in Qin⁃ling Mountains.④Compared with the First Fog⁃haze in 2019,the typical characters of aerosols during the fog⁃haze days in Xi′an were discovered:During the fog⁃haze days,the main component of PM_(2.5)was organic carbon with a maximum value larger than 40μg·kg^(-1);North wind with a mean wind speed larger than 6 m·s^(-1) played an important role during the disappearance of fog⁃haze in Xi′an,and the fog⁃haze in low troposphere would first dissipate.