Influence of weekdays, weekends and bandhas on surface ozone in Kathmandu valley

In this paper, variations of nitric oxide (NO), nitrogen dioxide (NO2), oxides of nitrogen (NOx), ozone (O3) and total oxidant (OX) concentration in ambient air of Kathmandu valley are presented. O3 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 O3 imply that the residual O3 remaining after the NO–NO2–O3 reaction chain controlled O3 concentration in the valley atmosphere and the radical channel was likely to have a minor contribution. The higher positive correlation coefficient for O3 variation during weekdays and bandhas, weekdays and weekends suggests common sources for the weekends and bandhas O3 variation. The higher O3 concentration during weekends and bandhas compared to weekdays was due to less destruction of O3. Enhanced reduction in traffic emission levels, enforcement of stringent emission standards within the valley and the surroundings may help to address the O3 problem in the valley atmosphere.