Heterogeneity in aerosol characteristics at the semi-arid and island AERONET observing sites in India and Maldives

Aerosol Opto-physical Properties: Temporal Variation, Aerosol Type Discrimination and Source Identification

“…Magnitude-wise, AODs at both wavelengths depict an increasing trend of about 0.05 year -1 (AOD500nm) and 0.03 year -1 (AOD1020 nm) during the period of observation despite AOD500 nm being almost 2-fold higher as compared to AOD1020 nm. The difference in AOD magnitudes at 500 and 1020 nm wavelengths can be attributed to the extinction efficiencies of the prevalent aerosol ensembles of different sizes active at each wavelength as per the Mie scattering theory (Quenzel 1970;Varpe et al, 2018). The Ångström turbidity coefficient, β, more or less follows the same trend of variation as is observed for AOD1020 nm.…”

“…The AOD is known to be the main physical parameter linked to the columnar integrated optical activity of aerosols. This is often retrieved through the measurements of extinction of sunlight at different wavelengths from the ground-based observations of direct beam solar irradiance (Pawar et al, 2012;Aher et al, 2014;Varpe et al, 2018) and also from the space-based instruments through the modeling of scattered radiation (Kahn et al, 2005;Sayer et al, 2012;Toledano et al, 2012;Levy et al, 2013;Li et al, 2014). Also, AOD is the most comprehensive variable to determine the atmospheric aerosol loading and radiative forcing retrievals.…”

“…AOD observation at different wavelengths is a valuable tool to infer aerosol size distribution as well as its spatio-temporal variation. Over the last few decades, a steady increase in scientific interest in the assessment of the aerosol opto-physical, chemical, and radiative properties has identified pivotal role of the atmospheric aerosols in the determination/modification of the Earth-atmosphere radiation balance and hydrological cycle through their direct and indirect effects (Augustine et al, 2008;Varpe et al, 2018). Mostly, the global warming phenomena have been attributed to enhanced greenhouse gas (GHG) emissions (Solomon et al, 2009).…”

“…A N U S C R I P T monsoon (0.47 ± 0.26) seasons (Patel et al, 2017). The existence of high MODIS/Terra AOD550 nm during monsoon season could be assigned to the effect of cloud contamination and relative humidity leading to the hygroscopic growth of atmospheric aerosols giving rise to high AOD during this season (Ramachandran and Cherian, 2008;Chew et al, 2011;Huang et al, 2012;Indira et al, 2013;Chelani, 2015;Varpe et al, 2018). The Microtops II Sun photometer measured AOD 500 nm during winter season is slightly higher than AOD in pre-monsoon which may be ascribed to the higher surface wind activity which may be responsible for lifting-up of soil-dust aerosols from dry lands and long-range transported dust from the arid regions (Aher et al, 2014).…”