Detection of surface emission hot spots, trends, and seasonal cycle from satellite-retrieved NO2 over India

Tropospheric NO2 concentrations derived from spaceborne measurements of Global Ozone Monitoring Experiment (GOME) on board ERS 2 and Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY) on board Envisat, respectively, for the time period of 1996-2006 have been used to identify major NO2 emission hot spots, trends, and seasonal cycle over different regions of India. Emission hot spots are observed over the locations of thermal power plants and over major urban and industrial regions. A multifunctional regression model has been used to analyze the trends and seasonal cycle over these emission hot spots. Increasing trends of similar to 1.65 +/- 0.52% a(-1) have been observed for NO2 over India. The fast growing industrial regions of Mumbai and Delhi show increasing trends of similar to 2.1 +/- 1.1 and similar to 2.4 +/- 1.2% a(-1), respectively. Seasonal variations of tropospheric NO2 concentrations show a maximum during winter-summer (December-May) and a minimum during the monsoon seasons (June-September). The observed seasonal cycle in satellite-derived NO2 agrees well with the surface-level observations of NOX.