Variability of tropospheric columnar NO2 and SO2 over eastern Indo-Gangetic Plain and impact of meteorology

Long-term analyses of monthly mean tropospheric NO2 and SO2 were performed over a period of January 2005 to December 2014, around few industrial areas (power plant clusters) in the Indo-Gangetic Plains. Alongside, similar studies have been conducted over some background mountain and rural sites, forest areas and small urban locations without large industries-all located in and around the Indo-Gangetic Plains. In these locations, the trend analyses of columnar NO2 and SO2 using satellite-based measurements from Ozone Monitoring Instrument (OMI) were performed to study their spatial, seasonal and long-term behaviour. Distribution of NO2 shows a large variation with major hot spots and average monthly values ranging between 0.03 and 0.35 Dobson Unit (DU), whereas the same for SO2 illustrates the range of average monthly values in between 0.13 to 1.00 DU. All the columnar values have been further correlated to meteorological parameters like cloud fraction, rainfall, outgoing longwave radiation flux and planetary boundary layer height. Analysis of the results indicates the influence of meteorology on the columnar concentration of these gases. Anomalous behaviour of SO2 during 2008 and 2011 were observed due to the long-range transport of volcanic SO2 over India from Dalaffilla and Nabro volcanoes, respectively. SO2/NO2 ratio was also observed to elicit the contribution of stationary (power plants and industries) source origins over mobile (automobile) sources towards the columnar burdens of these gases.