Ambient ozone over mid-Brahmaputra Valley, India: effects of local emissions and atmospheric transport on the photostationary state.

This study presents the characteristics of ground level atmospheric ozone (O) over the rural mid-Brahmaputra Valley region of the northeastern India. Ozone and oxides of nitrogen (NO = NO + NO) concentration data were obtained from continuous measurement of O and NO housed at the MAPAN-AQM station at Tezpur University. The meteorological parameters were obtained from the same station. The diel, monthly, and seasonal variations of O were studied. The O-NO photostationary state (PS) was carefully examined and it was found that the net O concertation deviated substantially from the PS during the winter season. The deviation could be attributed to local biomass burning, biogenic VOC emission from forest and agriculture, and long-range transport of peroxyacyl nitrate (PAN). The long-range transport has been ascertained by examining the ventilation coefficients (VC), which correlated with the steep growth of net O concentrations in the morning hours. The HYSPLIT air mass back trajectories were used in concentration-weighted trajectory (CWT) analyses of O to assess the long-range regional transport of O precursors, which positively influenced local O concentrations.