Black carbon aerosols over urban and high altitude remote regions: Characteristics and radiative implications

Temporal and seasonal variabilities in black carbon (BC) mass concentrations, equivalent BC from fossil fuel (BCff) and wood burning (BCwb) are investigated using multiwavelength aethalometer measurements made over urban (Ahmedabad) and high altitude remote (Gurushikhar) sites in western India during 2015-2016. BC, BCff and BCwb mass concentrations exhibit strong diurnal variation over Ahmedabad compared to Gurushikhar. Annual mean contribution of BCff to total BC mass concentration is estimated to be 80 and 72% respectively over Ahmedabad and Gurushikhar, which indicates the dominance of fossil fuel emissions. To delineate the impact of BC aerosols on the Earth atmosphere radiation budget aerosol radiative forcing due to composite aerosols, and BC aerosols alone is estimated. Maximum atmospheric forcing due to BC is observed during December (15 Wm(-2)) and November (8 Wm(-2)) over Ahmedabad and Gurushikhar respectively, because BC mass concentration is highest in the respective months. Surface composite forcing is higher during postmonsoon (-27 Wm(-2)) and premonsoon (-16 Wm(-2)) over Ahmedabad and Gurushikhar respectively due to high aerosol optical depths. BC aerosols contribute similar or equal to 60% to the shortwave atmospheric forcing. The present study shows that the large spatial and temporal variation in BC mass concentrations over an urban and high altitude remote site can produce significant regional variabilities in aerosol radiative effects.