Investigation on seasonal variations of aerosol properties and its influence on radiative effect over an urban location in central India

Abstract

Aerosol plays an important role in modulating solar radiation, which are of great concern in perspective of regional climate change. The study analysed the physical and optical properties of aerosols over an urban area and estimated radiative effect using three years in-situ data from sunphotometer, aethalometer and nephelometer as input to radiative transfer model. Aerosols properties indicate the dominance of fine mode aerosols over the study area. However presence of coarse mode aerosols is also found during pre-monsoon [March-April-May]. Daily mean aerosol optical depth showed a minimum during winter [Dec-Jan-Feb] (0.45–0.52) and a maximum during pre-monsoon (0.6–0.7), while single scattering albedo (ω) attains its maximum (0.78 ± 0.05) in winter and minimum (0.67 ± 0.06) during pre-monsoon and asymmetry factor varied in the range between 0.48 ± 0.02 to 0.53 ± 0.04. Episodic events of dust storm and biomass burning are identified by analyzing intrinsic aerosol optical properties like scattering Ångström exponent (SAE) and absorption Ångström exponent (AAE) during the study periods and it has been observed that during dust storm events ω is lower (∼0.77) than that of during biomass burning (∼0.81). The aerosol direct radiative effect at top of the atmosphere during winter is −11.72 ± 3.5 Wm−2, while during pre-monsoon; it is −5.5 ± 2.5 Wm−2, which can be due to observed lower values of ω during pre-monsoon. A large positive enhancement of atmospheric effect of ∼50.53 Wm−2 is observed during pre-monsoon compared to winter. Due to high aerosol loading in pre-monsoon, a twofold negative surface forcing is also observed in comparison to winter.