Estimates of Carbonaceous Aerosol Radiative Forcing over a Semiurban Environment in Garhwal Himalayas

Abstract

Continuous sampling of particulate matter (PM2.5) was carried out over Srinagar, a semiurban site in Garhwal Himalayas, during January to December 2017. The organic and elemental carbon (OC and EC) values were extracted from PM2.5 samples using a Thermo optical OC/EC analyzer. The radiative forcing due to carbonaceous aerosols was estimated using an optical model along with a radiative transfer model. The EC mass was found to be up to 7 µg m−3, while the OC peaked at 17 µg m−3 during the experimental period. The EC forcing was found to range from − 18.32 ± 3.91 W m−2 to − 28.18 ± 8.09 W m−2 at the surface and + 8.57 ± 2.15 W m−2 to 13.83 ± 3.48 W m−2 at the top of the atmosphere (TOA), inducing atmospheric forcing of + 27.24 ± 5.09 to + 42.02 ± 11.32 W m−2 over Srinagar in different months. On the other hand, the OC forcing was found to be much weaker compared with the EC forcing, being + 1.37 ± 0.95 to + 2.342 ± 1.67 W m−2 in the atmosphere in different seasons. The forcing efficiency was estimated to determine the projection of the radiative forcing per unit optical depth, yielding a range of 271.94 ± 94 to 450.03 ± 59.11 W m−2 AOD−1 in the atmosphere for EC and 19.51 ± 9.13 to 36.96 ± 10.97 W m−2 AOD−1 for OC. The atmospheric heating rates of OC/EC were extracted and found to be 0.954 ± 0.31 to 1.46 ± 0.58 K day−1 for EC and 0.047 ± 0.023 to 0.081 ± 0.035 K day−1 for OC over Srinagar.