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

Abstract: Monthly mean tropospheric column O3 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 O3 and NO2 over the study region was ∼15–20 DU and ∼0.03–0.1 DU, respectively. Latitudinal gradient of −0.84 DU/° and 0.005 DU/°, respectively has been estimated for O3 and NO2 over this region. High levels of O3 were measured over parts of Arabian Sea and Bay of Bengal owing to transport from adjacent landmass. The dependence of O3 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 O3 seasonal patterns associated with differences in NO2, availability of solar radiation and prevailing airmass. BLH plays a role in the seasonal variation of tropospheric O3. The long-term trend in tropospheric O3 over a period of ten years has been examined for the different regions and both positive and negative trends were observed. [Copyright &y& Elsevier]