In this paper, variations of nitric oxide (NO), nitrogen dioxide (NO2), oxides of nitrogen (NOx), ozone (O-3) and total oxidant (O-X) concentration in ambient air of Kathmandu valley are presented. O-3 behavior during weekdays, weekends and bandhas (general strike) is analyzed and the mechanism related to it is discussed. The increased NO2/Ox ratio with increasing NOx concentration and the inverse relation between NOx and O-3 imply that the residual O-3 remaining after the NO-NO2-O-3 reaction chain controlled O-3 concentration in the valley atmosphere and the radical channel was likely to have a minor contribution. The higher positive correlation coefficient for O-3 variation during weekdays and bandhas, weekdays and weekends suggests common sources for the weekends and bandhas O-3 variation. The higher O-3 concentration during weekends and bandhas compared to weekdays was due to less destruction of O-3. Enhanced reduction in traffic emission levels, enforcement of stringent emission standards within the valley and the surroundings may help to address the O-3 problem in the valley atmosphere.