Tropospheric column O3 and NO2 over the Indian region observed by Ozone Monitoring Instrument (OMI): Seasonal changes and long-term trends

Monthly mean tropospheric column O-3 and NO2 retrieved from Ozone Monitoring Instrument on board Aura for the period December 2007 to November 2008 have been analysed to study the spatial and seasonal variations at selected locations over the Indian landmass and surrounding oceanic region. The annual change in tropospheric O-3 and NO2 over the study region was similar to 15-20 DU and similar to 0.03-0.1 DU, respectively. Latitudinal gradient of -0.84 DU/degrees and 0.005 DU/degrees, respectively has been estimated for O-3 and NO2 over this region. High levels of O-3 were measured over parts of Arabian Sea and Bay of Bengal owing to transport from adjacent landmass. The dependence of O-3 on NO2, solar radiation, cloud cover, rainfall, fire count, outgoing longwave radiation and boundary layer height (BLH) were investigated in detail along with the airflow pattern and airmass back trajectory analysis. There were regional variations in O-3 seasonal patterns associated with differences in NO2, availability of solar radiation and prevailing airmass. BLH plays a role in the seasonal variation of tropospheric O-3. The long-term trend in tropospheric O-3 over a period of ten years has been examined for the different regions and both positive and negative trends were observed. (C) 2012 Elsevier Ltd. All rights reserved.