Diurnal variations in ozone do not show a daytime build up, while, CO and NOy generally show higher levels during daytime and lower levels during nighttime at Nainital. It is shown that the diurnal variations in these gases are mainly governed by the dynamical processes including upslope downslope mountain winds and the boundary layer evolution and associated convective mixing. This is confirmed by the simulated vertical wind and the boundary layer height using WRF model. Seasonal variations in ozone, CO and NOy at Nainital are characterized by spring maxima and summer-monsoon minima. This seasonality is found in good agreement with the variability of weather parameters. Seasonality in CH4 and light (C2-C5) NMHCs shows a late autumn and early winter maxima and summer monsoon minima. This has been attributed to the post monsoon pattern along with the long range transport of pollutants during winter while regional pollution along with biomass burning activities plays key role for springtime maxima of ozone, CO and NOy. The classification based on the air-mass residence time shows ozone, CO and NOy, levels of 57±14 ppbv, 206±125 ppbv, and 1856±1596 pptv in the continental and 25±11 ppbv, 120±50 ppbv, and 336.6±211 pptv in the marine air-mass, respectively. The enhancements in ozone, CO and NOy during high fire activity period are estimated to be 4-18%, 15-76% and 35-51% respectively. Higher CO/NOy ratio during winter indicate minimal influence of local activities.