Seasonal characteristics of SO2, NO2, and CO emissions in and around the Indo-Gangetic Plain.

Anthropogenic emissions of sulfur dioxide (SO2), nitrogen dioxide (NO2), and carbon monoxide (CO) exert significant influence on local and regional atmospheric chemistry. Temporal and spatial variability of these gases are investigated using surface measurements by the Central Pollution Control Board (India) during 2005-2009 over six urban locations in and around the Indo-Gangetic Plain (IGP) and supported using the satellite measurements of these gases. The stations chosen are Jodhpur (west of IGP), Delhi (central IGP), Kolkata and Durgapur (eastern IGP), Guwahati (east of IGP), and Nagpur (south of IGP). Among the stations studied, SO2 concentrations are found to be the highest over Kolkata megacity. Elevated levels of NO2 occur over the IGP stations of Durgapur, Kolkata, and Delhi. Columnar NO2 values are also found to be elevated over these regions during winter due to high surface concentrations while columnar SO2 values show a monsoon maximum. Elevated columnar CO over Guwahati during pre-monsoon are attributed to biomass burning. Statistically significant correlations between columnar NO2 and surface NO2 obtained for Delhi, Kolkata, and Durgapur along with very low SO2 to NO2 ratios (≤0.2) indicate fossil fuel combustion from mobile sources as major contributors to the ambient air over these regions.