The impact of increases in South Asian anthropogenic emissions of SO 2 on sulfate loading in the upper troposphere and lower stratosphere during the monsoon season and the associated radiative impact

Abstract. The Asian summer monsoon plays a key role in changing aerosol amounts in the upper troposphere and lower stratosphere (UTLS) via convective transport. Here, we use the ECHAM6-HAMMOZ global chemistry–climate model to investigate the transport of anthropogenic South Asian sulfate aerosols and their impact on the UTLS. Our experiments (ten-member ensemble) with SO2 emissions enhanced by 48 % over South Asia, based on an Ozone Monitoring Instrument (OMI) satellite observed rising trend of ~ 4.8 % per year during 2006–2017, simulate how the Asian sulfate aerosols are convectively transported to the UTLS. The tropospheric increase in SO2 leads to an increase in UTLS sulfate aerosol loading of 10–33 % over South Asia and 5–10 % over the high latitudes in the northern hemisphere. The enhanced sulfate aerosols lead to warming (0.1 ± 0.06 to 0.6 ± 0.25 K) in the lowermost stratosphere and cooling (−0.1 ± 0.06 to −0.8 ± 0.41 K) in the troposphere in the Northern Hemisphere. The estimated mean direct radiative forcing at the top of the atmosphere (TOA) induced by the increase in South Asian aerosol emissions is −0.2 to −1.5 W m−2 over north India during the monsoon season. The decrease in vertical velocity and the associated enhanced stability of the upper troposphere in response to increased SO2 emissions will likely have a weakening effect on the South Asian monsoon.