Surface ozone (O-3), black carbon (BC) concentration and their relationship were established with PM10 and PM2.5 mass concentration at Mohal (31.9 degrees N, 77.12 degrees E, 1154 m amsl), a semi-urban site, in the Kullu valley of the northwestern part of the Indian Himalaya during January to December, 2010. O-3 showed highest diurnal variation (84 ppb) during daytime and lowest (10 ppb) during late evening as well as early morning hours. The maximum concentration of O-3 during summer was influenced by meteorological parameters, high insolation and backward airmass trajectories with transported pollutants. Rate of increase of O-3 was observed as high as 2.92 ppb h(-1) in October, followed by 2.73 ppb h(-1) in March and 2.71 ppb h(-1) in May. However, it was low 1.89 ppb h(-1) in February. Monthly average concentration of O-3 showed distinct seasonal variations with maximum in summer (55.9 +/- 9.3 ppb in May) and minimum in winter (30.0 +/- 6.2 ppb in January). Most of the O-3 episodes were observed in summer during fair weather conditions like high solar flux (480-500 W m(-2)), relatively high temperature (22-24 degrees C) and negligible rainfall. By applying back-ward trajectory Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model, the origin of the airmasses contributing to the background O-3 concentration was investigated. O-3 showed negative correlation with BC (r = -0.42). BC contributed 10-20% and 14-42% to the total aerosol mass concentration of PM10 and PM2.5 respectively which showed positive correlation (r = 0.65) with PM10 as well as PM2.5 aerosol mass concentration. (C), 2013 Elsevier Ltd. All rights reserved.