Columnar-integrated aerosol optical properties and classification of different aerosol types over the semi-arid region, Anantapur, Andhra Pradesh.

This study presents a characterization of aerosol columnar properties measured at a semi-arid station Anantapur in the southern part of India during the period from October 2012 to September 2013. Aerosol optical depth (AOD) and Angstrom exponent (α) have been retrieved from Microtops II Sunphotometer over the observation site. The results show that a pronounced spectral and monthly variability in the optical properties of aerosols is mainly due to anthropogenic sources. The results show that the spectral curvature can effectively be used as a tool for aerosol type discrimination, since the fine-mode aerosols exhibit negative curvature, while the coarse-mode particles are positive. The classification of aerosols is also proposed by using the values of AOD at 500 nm and Angstrom exponent values (α(380-870)) by applying threshold values obtained from the frequency distribution of AOD. The results of the analysis were identified by four individual components (anthropogenic/biomass burning, coarse/dust, coarse/marine, clean continental) of different origin and compositions. The most frequent situations observed over the site are that due to the anthropogenic/biomass burning situations which account for about 45.37%, followed by coarse/dust (43.64%), clean continental (7.2%) and coarse/marine (3.82%) during summer. The identification of the aerosol source type and the modification processes are analyzed by using the Gobbi et al. (2007) classification scheme based on the measured scattering properties (α, dα) derived from the Microtops II Sunphotometer.