The spatio-temporal variation in black carbon (BC) mass concentration and total aerosol optical properties simulated from regional climate model RegCM Versions 4.3, 4.4 and 4.5 are investigated and compared with in situ and remote sensing measurements. Higher BC mass concentrations (>3 mu g m(-3)) are found over the Indo-Gangetic Basin (IGB) in all versions. BC mass in RegCM 4.4 and 4.5 are closer to observations. BC mass estimated from RegCM 4.4 and 4.5 is found to agree within 20% with respect to observation during pre-monsoon and monsoon seasons. The differences in observed and simulated mass are >50% during winter over all locations and during winter and post-monsoon over western India, which suggests the need of improvement in emission inventory over the region, as emissions from the biofuel and crop residue burning in agriculture are very low in the emission inventories. RegCM 4.3, 4.4 and 4.5-simulated aerosol optical depths (AODs) are found to have more than 40% underestimation during winter and the post-monsoon over Kanpur, while 4.3 overestimates AOD during the pre-monsoon and monsoon seasons over Kanpur, and during all seasons except winter over Gandhi College. Single scattering albedo (SSA) values range from 0.75 to 0.95 in 4.4 and 4.5. Lower SSA values are found over the IGB where anthropogenic emissions dominate. SSA simulated by RegCM 4.4 and 4.5 are lowered by 2-10% with respect to aerosol robotic network (AERONET)-derived SSA. Moreover, during winter such differences are higher (>10%). The RegCM 4.4 and 4.5-simulated BC mass concentrations are nearer to observations, while for columnar optical properties, RegCM 4.3 is more close to measurement. BC mass is 10-30% closer to observations when model for ozone and related chemical tracers-chemical transport model chemical boundary condition are utilized in addition to CAM + EC-EARTH.