Seasonal Evolution of Sulfur Dioxide Over the Indian Subcontinent

Reanalysis, which combines the chemical-transport model with remote-sensing measurements, has shown potential to fill data gaps over observationally sparse regions of the globe. Here, the seasonal distribution of sulfur dioxide (SO2) over the Indian region was analyzed for 2005–2015 period using Copernicus Atmosphere Monitoring Service (CAMS) reanalysis. CAMS reproduced general features and seasonality observed in surface SO2 over this region. Elevated levels were revealed across the Indo-Gangetic Plain (IGP) and over eastern and central India. SO2 shows a prominent seasonality over India, with a maximum typically during winter and a minimum during the summer monsoon. The winter maximum is attributed to weaker chemical sink, stagnant meteorological conditions, and elevated emissions, whereas wet scavenging, inflow of marine air, and stronger sulfate formation efficiency cause lower SO2 during the monsoon. SO2 levels exhibited an enhancement over IGP and central and eastern India, with rates in the range of 0.5 ppbv to 4 ppbv per decade. Like the distribution, trends also showed seasonal dependence, with weaker trends during the summer monsoon and stronger trends during the winter and postmonsoon. In situ observations of SO2 and related species especially over the identified hot spots are recommended to validate satellite and model data sets and evaluate airquality and climate implications.