Ground based observations of AOD, aerosols number concentrations and BC are made at Nainital (29.4 °N, 79.5 ºE, 1958 m amsl), a high altitude site in the central Himalayas, under ISRO-ARFI project. Surface observations of BC and AOD are also made at Pantnagar (29.0 °N, 79.5 ºE, 231 m amsl) under this project. Generally, AOD, aerosols number concentrations and BC shows a major peak during spring followed by autumn at Nainital. The BC mass concentration is found to be maximum (1.35 ± 0.74 µgm-3) in spring (Mar-May) and minimum during summer/monsoon (Jun-Aug) season (0.69 ± 0.52 µgm-3). Further BC is 0.90 ± 0.60 µgm-3 in autumn (Sep-Nov) and 1.00± 0.65 µgm-3 in winter (Dec-Feb) season at Nainital. The concentration weighted trajectories indicate that the regions nearby to the Nainital and other northern Indian regions having significant BC mass concentrations during spring time. It is found that the AOD as well as BC shows significant enhancement during the biomass period (April–May). The fine mode (0.3-1.0 µm) number concentration also increases abruptly during the fire-activity period. The enhanced BC and AOD (0.5 µm) due to biomass burning are estimated to be 1.80 µgm-3 (∼145%) and 0.3 (∼150%) respectively, which leads to additional atmospheric warming of 19 W m−2 and increases the lower atmospheric heating rate by 0.8 K day−1. The AOD as well as BC at Pantnagar are quite high as compared to that at Nainital. The diurnal variation of BC at Pantnagar is entirely different than at Nainital resulting in two peaks one in morning (0700-0900 hrs) and another in evening (1700 to 2100 hrs) hours. The average BC mass concentration at Pantnagar during winter seasons is found to be ~7.9±5.2 µgm-3 which is ~44% higher than the annual mean value. BC concentration gets reduced during the spring season and an average concentration of ~4.8±3.6 µgm-3 was observed in spring. The BC mass concentration during the summer/monsoon seasons reduces to a concentration of ~2.8±2.8 µgm-3 and is ~6.5±4.9 µgm-3 in autumn. The ground based observations at both the sites have been used in radiative estimations of aerosols and other properties extensively at both the sites.