Climatological aspects of size-resolved column aerosol optical properties over a rural site in the southern peninsular India

We present the long-term (2008-2018) climatological characteristics of column aerosol optical properties from the Sky Radiometer at Gadanki (13.48 degrees N, 79.18 degrees E), a typical rural site in southern peninsular India. A method to separate the fine and coarse mode spectral aerosol optical properties was presented. The climatological aspects related to the diurnal, monthly, and intra-annual variations of observed aerosol optical properties exhibited both seasonal and spectral dependence. While the size-resolved aerosol optical depth (AOD), absorption aerosol optical depth, and asymmetry parameter exhibited a decreasing trend, single scattering albedo (SSA) showed an increasing trend from shorter to longer wavelengths in all seasons with distinct magnitudes. Seasonal asymmetry in the diurnal variation of AOD and Angstrom exponent was observed. Intra-annual variability clearly indicated distinct fine and coarse mode dominance during winter and monsoon, respectively, while mixed contributions were found in other seasons. This is attributed to the influence of prevailing air masses on the column aerosol properties. Annual mean SSA values indicated the dominance of moderately absorbing (0.91) to weakly absorbing (0.95) aerosols. On evaluating the size-resolved AOD (at 500 nm) with those from extended Spectral Deconvolution Algorithm (SDA+), the observed differences are found to be remarkable for coarse mode AOD although the correlations for both fine and coarse AODs were observed to be 0.96. Lastly, the Dark Target and Deep Blue merged AOD (at 550 nm) from MODIS Terra/Aqua are evaluated to examine the consistency with ground measurements and both have shown a systematic underestimation with an increase in the magnitude of AOD strongly dependent on the seasons. These results form a basis for the comprehensive characterization of aerosol types and associated radiative impacts that are vital for understanding the regional climate change.

Automated summary

The study presents the climatological characteristics of aerosol optical properties in a rural site in southern peninsular India from 2008 to 2018, revealing variations in aerosol optical properties across different seasons and spectral dependencies. The intra-annual variability indicates a dominance of fine and coarse mode aerosols during winter and monsoon, respectively, while mixed contributions are found in other seasons.