Abstract:

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.

Key words: Fenwei Plain, Haze and sand, Satellite data, Hybrid single-particle lagrangian integrated trajectory model (HYSPLIT)