Impact of winter droughts on air pollution over Southwest China.

The meteorological causes of winter droughts over Southwest China (SWC) have been widely investigated in recent years; however, little information is available on the impact of these droughts on air pollution. This study (1) characterized and quantified the impact of winter droughts on air pollution over SWC and (2) investigated the atmospheric teleconnections associated with the winter droughts in this region using air pollution monitoring data, routinely observed meteorological data, and National Centers for Environmental Prediction/National Center for Atmospheric Research and ERA-Interim reanalysis data. The main results are as follows: (1) A surface high pressure system together with a weak descent in the middle troposphere was the main cause of the SWC drought in December 2017. (2) It has been found that precipitation, the number of precipitation days and the atmospheric boundary layer height all decreased during the droughts, resulting in unfavorable conditions for the dispersion of air pollutants. (3) The concentrations of PM and PM were much higher during dry periods than those during non-dry periods over SWC, especially in the Sichuan Basin of the SWC. (4) WRF-Chem simulations reproduced the observed changes in air pollutant concentrations between dry and non-dry conditions. (5) Atmospheric teleconnections associated with the winter droughts in SWC were negative phases of the conventional Eurasian teleconnection, Eastern Atlantic/Western Russia pattern, Arctic Oscillation and North Atlantic Oscillation, and a La Niña event. Overall, this study provides scientific support for the long-term potential and accurate short-term predictions of air pollution in SWC.