The impact of recent changes in Asian anthropogenic emissions of SO2 on sulfate loading in the upper troposphere and lower stratosphere and the associated radiative changes

Convective transport plays a key role in aerosol enhancement in the upper troposphere and lower stratosphere (UTLS) over the Asian monsoon region where low-level convective instability persists throughout the year. We use the state-of-the-art ECHAM6-HAMMOZ global chemistry-climate model to investigate the seasonal transport of anthropogenic Asian sulfate aerosols and their impact on the UTLS. Sensitivity simulations for SO2 emission perturbation over India (48% increase) and China (70% decrease) are performed based on the Ozone Monitoring Instrument (OMI) satellite-observed trend, rising over India by similar to 4.8% per year and decreasing over China by similar to 7.0% per year during 2006-2017. The enhanced Indian emissions result in an increase in aerosol optical depth (AOD) loading in the UTLS by 0.61 to 4.17% over India. These aerosols are transported to the Arctic during all seasons by the lower branch of the Brewer-Dobson circulation enhancing AOD by 0.017% to 4.8 %. Interestingly, a reduction in SO2 emission over China inhibits the transport of Indian sulfate aerosols to the Arctic in summer-monsoon and post-monsoon seasons due to subsidence over northern India. The region of sulfate aerosol enhancement shows significant warming in the UTLS over northern India, south China (0.2 +/- 0.15 to 0.8 +/- 0.72 K) and the Arctic (similar to 1 +/- 0.62 to 1.6 +/- 1.07 K). The estimated seasonal mean direct radiative forcing at the top of the atmosphere (TOA) induced by the increase in Indian SO2 emission is -0.2 to -1.5 W m(-2) over northern India. The Chinese SO2 emission reduction leads to a positive radiative forcing of similar to 0.6 to 6 W m(-2) over China. The decrease in vertical velocity and the associated enhanced stability of the upper troposphere in response to increased Indian SO2 emissions will likely decrease rainfall over India.