Surface based observations of O3, CO, light NMHCs and BC were made during the international field campaign SusKat-ABC during Dec 2012–June 2013 in the Kathmandu valley and surrounding regions. The diurnal variations at Bode were typical of a polluted urban site with sharp day time build up in O3, and CO having higher levels during morning/evening hours. The early morning CO levels were higher during winter (Jan-Feb, ~ 1500 ppbv) than spring (Mar-May, ~1100 ppbv). However, daytime O3 levels were slightly higher during spring (~62 ppbv) when compared with those during winter (~54 ppbv). High resolution WRF-Chem setup was done over Kathmandu valley (9, 3, 1 km). Large differences in the meteorological parameters were observed with nightime differences being the highest. Differences in temperature and RH were ~1 oC, 10% during daytime and 4-8 oC, 40-60% during night-time respectively. Wind speeds and directions were in good agreement. Model was warm and drier during night time and was unable to capture fog at night. The day and night-time differences in O3 were ~25 and ~50ppb respectively and CO showed even larger day/night differences 100-200 ppb during daytime and 500-1500 ppb at night. These differences improved with some modifications in model but still large differences were observed at Bode. The similar differences in meteorology at a mountain top Nagarkot was much lower (<10%) and model performed well there.