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

• Published in: Atmospheric Chemistry and Physics
• Main Authors: Fadnavis, Suvarna, Müller, Rolf, Kalita, Gayatry, Rowlinson, Matthew, Rap, Alexandru, Li, Jui-Lin Frank, Gasparini, Blaž, Laakso, Anton
• Format: Text
• Language: English
• Published: 2019
• Subjects: Arctic; Indian
• Online Access: https://doi.org/10.5194/acp-19-9989-2019; https://www.atmos-chem-phys.net/19/9989/2019/

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 SO 2 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 SO 2 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 ( <math xmlns="http://www.w3.org/1998/Math/MathML" id="M8" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>∼</mo><mn mathvariant="normal">1</mn><mo>±</mo><mn mathvariant="normal">0.62</mn></mrow></math> <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="51pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="6b8d82df5c23f66fffe20f5420b1c3f8"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-9989-2019-ie00001.svg" width="51pt" height="10pt" src="acp-19-9989-2019-ie00001.png"/></svg:svg> 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 SO 2 emission is − 0.2 to − 1.5 W m −2 over northern India. The Chinese SO 2 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 SO 2 emissions will likely decrease rainfall over India.