Distribution of sulfur dioxide over Indian subcontinent: Remote sensing observations and model reanalysis

Sulfur dioxide (SO 2 ) is a short-lived reactive trace gas, which plays vital roles in air quality, tropospheric chemistry and climate. Rapid changes in the technologies and expansion of energy sector is anticipated to have influenced the distribution of SO 2 across the Indian subcontinent, however continuous in situ observations are scarce. In this direction, we investigate the spatio-temporal distribution of SO 2 over the Indian region combining the remote sensing observations from space (OMI), in situ measurements (CPCB), and results from the global models (MERRA-2 and CAMS) for 2005-2015 period. The comparison of MERRA-2 results with surface SO 2 observations show model's ability to reproduce the general aspects of SO 2 distribution over this region. Analysis of the long-term MERRA-2 and CAMS simulations reveal an enhancement in the SO 2 levels, more pronounced over the industrial regions in the north, east and central India at rates in range of 0.1-0.3 ppbv $\mathrm{y}\mathrm{r}^{-1}$ during 2005-2015 period. This concord well with the trends based on satellite-based observations and emission inventories over this region. These changes in SO 2 are further found to impact the regional distribution of the sulphate aerosols significantly.We estimated higher efficiency of sulphate formation during monsoon (0.30) than that during winter (0.15). This study highlights a need to conduct in situ observations of SO 2 over a network of stations especially in the identified regions of stronger SO 2 enhancements to understand the impacts on the regional air quality and climate.