Modelling the deep convective transport of trace gases (CO, NH3 and SO2) from the planetary boundary layer to the Asian summer monsoon anticyclone

Abstract

Deep convection plays a vital role in transporting Asian pollutants from the planetary boundary layer (PBL) into the Asian summer monsoon anticyclone (ASMA). However, the efficiency and effectiveness of transporting pollutants with various chemical and physical properties to the ASMA remain unclear. In this study, we use the global atmospheric chemistry and climate model EMAC to investigate the deep convective transport of trace gases such as CO, NH3 and SO2 from the PBL to the ASMA over the years 2010–2020. We quantify the deep convective transport efficiency of different trace gases into the ASMA. We show that the strongest convective transport tendency occurs over northern India and the southern edge of the Tibetan Plateau for CO (0.2–0.5 ppbv h−1), over the south and eastern parts of the Tibetan Plateau for NH3 (0.02–0.05 ppbv h−1), and over central India and eastern China for SO2 (0.002–0.005 ppbv h−1). We find that, in contrast to CO and NH3, the SO2 enhancements within the ASMA are very weak, and there can even be a decrease in SO2 over the southern Tibetan Plateau relative to the surroundings. Our analysis indicates that gas-liquid partitioning in clouds and subsequent wet deposition over South Asia are more effective at reducing SO2 than NH3 reaching the Tibetan Plateau and the ASMA. In view of ongoing changes in regional emissions, the effects of deep convective transport of various pollutants and associated gas-aerosol-cloud interactions on the chemical features of the ASMA require continued investigation.