Cluster analysis of aerosol properties retrieved from a sky-radiometer over a coastal site: Thiruvananthapuram, India

The present work analysed the characteristics of aerosol optical, physical properties over Thiruvananthapuram, a coastal site in southern part of India using Sky-radiometer (Model POM-02, Prede Co. Ltd, Japan) for a period 2011-2015. The lowest value of AOD was found during winter season which was followed by monsoon season. The highest value of AOD was found in pre-monsoon. The Angstrom Exponent which characterizes the size of the aerosols, decreases from January to June and increases from June to December months. The monthly back trajectory analysis using HYSPLIT describes the source of air masses for the station. The fine mode particles are dominant during winter season, which may be associated with the anthropogenic emissions and long range transport. A gradual increase in the coarse mode aerosol load was found from pre-monsoon season to the monsoon season, because of the large air mass coming from the ocean. A decrease in coarse mode aerosol was found during the post-monsoon period, due to the preferential washout of coarse mode particles during monsoon season. The result showed the dominance of mixed type aerosols during all seasons. The C1 cluster originating from Bay of Bengal contributed 29.8% of ensemble of trajectories, C2 cluster from Arabian Sea 31.9%, C3 cluster from the Indian Ocean (Northern hemisphere) 18.0%, and C4 cluster Indian Ocean (Southern hemisphere) 20.3%.