Characterization of aerosol optical properties and model computed radiative forcing over a semi-arid region, Kadapa in India

Abstract In this paper, we present the optical and radiative properties of aerosols for the first time measured at Yogi Vemana University (YVU) campus (14.47°N, 78.82°E, 138 m above sea level), Kadapa, a semi-arid region in southern India during December 2013–February 2015. The collocated measurements of aerosol optical depth (AOD) and black carbon (BC) mass concentration are carried out at Kadapa using the ten channels Multi-Wavelength solar Radiometer (MWR) and seven wavelengths Aethalometer, respectively. This work mainly focused on studying the temporal and spectral behavior of aerosol properties, and their implications to the aerosol direct radiative forcing (ADRF). The respective seasonal mean values of AOD at 500 nm were found to be 0.33 ± 0.01, 0.46 ± 0.05, 0.27 ± 0.02 and 0.37 ± 0.06 during the winter, summer, monsoon and post-monsoon, with an annual mean of 0.38 ± 0.18. It is revealed that the Angstrom exponent (AE or α 380–850 ) value was observed to be maximum (minimum) in March (July) with 1.75 ± 0.19 (0.65 ± 0.14) indicates a predominance of fine (coarse) mode aerosols. Added to this, the diurnal variations of BC mass concentration exhibited two maxima with peaks occurred during 07:00–08:00 h and 20:00–21:00 h local time (LT), and a minimum of the afternoon hours around 13:00–16:00 h LT. Further, the AOD-AE relationship was investigated over Kadapa, and the results conclude that the urban-industrial/biomass burning (UI/BB) type aerosols are more dominated during the study period. The OPAC model retrieved single scattering albedo (SSA) at 500 nm was found to vary between 0.83 and 0.92 with relatively lower values during winter, suggest an increase in absorbing type aerosols produced from anthropogenic activities. The SBDART model computed seasonal averaged ADRF within the atmosphere (ADRF ATM ) was found to be 26.7 ± 2.3, 25.1 ± 1.0, 17.8 ± 3.9 and 18.3 ± 2.6 W m −2 during the summer, winter, monsoon and post-monsoon seasons, respectively at Kadapa. This illustrated that the absorption of solar radiation in the ATM is high which produces a significant amount of heating effect, resulted in a maximum atmospheric heating rate of 0.75 K day −1 .