汾渭平原一次沙尘和人为混合空气污染过程分析

利用MODIS、OMI和CALIPSO卫星资料，结合地面环境监测数据、气象观测数据和后向轨迹模式（Hybrid Single Particle Lagrangian Integrated Trajectory Model，HYSPLIT），对汾渭平原2018年11月23日至12月6日沙尘和人为混合空气污染过程进行分析。结果表明：11月26日至12月3日为污染最重时段，其中12月1日为霾最重时段，11月26日夜间和12月2日夜间为沙尘影响最重时段；西安、临汾和洛阳重污染持续时长分别为66 h、42 h和37 h；污染过程累计持续336 h，其中199 h的相对湿度超过50%，沙尘期间，相对湿度较小；霾过程中，西安以本地积累和西南、东北方向的外来传输作用为主，临汾以本地积累为主，洛阳以东北方向的外来传输作用为主；西安、洛阳沙尘传输方向分别为西南和西北方向，临汾受沙尘传输影响较小。霾天气时，气溶胶光学厚度（AOD）高值空间分布受地形影响较大，吸收性气溶胶指数（AAI）较低，集中在距地面1.5 km高度内污染物最多，低层以污染沙尘为主；沙尘天气时，AOD和AAI值很高，分别可达2.0和4.5以上，集中在边界层内污染物最少，低层以沙漠沙尘为主；霾沙混合天气时集中在边界层内污染物居中，低层以沙漠沙尘和污染沙尘为主。HYSPLIT显示，前一次沙尘来源于新疆，传输距离更远，高度更高，速度更快，后一次沙尘来源于内蒙古西部，在汾渭平原造成污染更重。

Analysis of an air pollution event due to dust and anthropogenicemission in Fenwei Plain

Using the data retrieved from the Moderate Resolution Imaging Spectroradiometer(MODIS)satellite,the Ozone Monitoring Instrument(OMI),and the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation(CALIPSO),ground environmental monitoring and meteorological observational data,and a backward trajectory model(Hybrid Single-Particle Lagrangian Integrated Trajectory Model,HYSPLIT),we analyzed the air pollution progress caused by dust and anthropogenic emission in Fenwei Plain from November 23 to December 6,2018.The results showed that the severest air pollution occurs from November 26 to December 3,with the heaviest haze and dust pollution on December 1 and the heaviest dust pollution during the night on November 26 and the night on December 2.Heavy pollution lasts for 66 h,42 h,and 37 h in Xi′an,Linfen,and Luoyang,respectively,and the total duration of the pollution process is 336 h,of which the relative humidity is more than 50%in 199 h,but not for the dust episodes.The haze episode in Xi′an is predominately caused by air pollutants accumulated locally and transported from the southwest and northeast.Haze in Linfen is mainly due to local accumulation of pollutants,and haze in Luoyang mainly resulted from pollutants transported from the northeast.Dust particles are mainly transported from the southwest to Xi′an and from the northwest to Luoyang,respectively,and Linfen is influenced less by dust.During the haze episode,the spatial distribution of high values of aerosol optical depth(AOD)is greatly affected by topography,and the values of absorbing aerosol index(AAI)are low.Air pollutants are mainly concentrated under 1.5 km above the ground,with polluted dust predominately trapped at the lower altitudes.During dust episodes,both AOD and AAI are high,exceeding 2.0 and 4.5,respectively.Pollutant concentration is least in the planetary boundary layer(PBL),and dust is the major pollutant at the lower altitudes.Whereas in the haze-dust mixed episode,pollutant concentration in the PBL is relatively higher,and the major pollutants at the lower altitudes include desert dust and polluted dust.The analysis from the HYSPLIT model shows that dust particles in the former dust episode are generated from the Xinjiang Uygur Autonomous Region and transported longer and higher,and traveled faster than those of the second haze-dust mixed episode that come from the west of Inner Mongolia Autonomous Region,causing severer pollution in Fenwei Plain.