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

• Main Authors: Fadnavis, S, Müller, R, Kalita, G, Rowlinson, M, Rap, A, Li, J-LF, Gasparini, B, Laakso, A
• Format: Article in Journal/Newspaper
• Language: English
• Published: European Geosciences Union 2019
• Subjects: Arctic; Indian
• Online Access: https://eprints.whiterose.ac.uk/150294/; https://eprints.whiterose.ac.uk/150294/1/acp-19-9989-2019.pdf

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 ∼4.8 % per year and decreasing over China by ∼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 (∼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 ∼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.