Tropospheric NO2 Trends over South Asia during the Last Decade (2004-2014) Using OMI Data

The focus of this study is to assess spatiotemporal variability of tropospheric NO2 over South Asia using data from spaceborne OMI during the past decade (2004-2015). We find an average value of NO2 1.0 +/- 0.05 x 10(15) molec/cm(2) and a significant decadal increase of 14%. The elevating NO2 pollution over the region is linked to rise in motor vehicles and industrial and agricultural activities and increase in biomass fuel usage. The observed seasonality of NO2 is associated with change in meteorological conditions and seasonal cycles of anthropogenic emissions. OMI data reveal a seasonal peak in spring followed by winter largely linked to metrological conditions and anthropogenic emissions from crop residue and biomass burning for heating purpose, and low concentration in summer is mostly attributed to meteorological conditions. Significant increase, up to 42%, in NO2 concentrations over northwestern IGB, is observed connected to large scale postmonsoon crop residue events of 2010 and 2012. It is seen that NO2 is mounting over all the hotspot locations and most of the cities. Dhaka shows the highest increase of 77% followed by Islamabad (69%), Kabul (68%), Korba (64%), Bardhaman (47%), and Lahore (40%). On the contrary, DG Khan has shown negative trend of -11%.