Large aerosol optical depths observed at an urban location in southern India associated with rain-deficit summer monsoon season

Abstract

Aerosol spectral optical depth (AOD) measurements were made covering three years (2001, 2002 and 2003) at an urban continental location, Bangalore (13°N, 77.6°E) in India. These ground-based observations have shown that AODs reach a maximum during April (~0.5 at 500nm) and minimum during the November to January period (~0.2). The Angstrom wavelength exponent (α) was ~1.1 during the dry season (December to April), which, in conjunction with the high optical depth indicates significant anthropogenic influence. Seasonal variations in AODs appear to have an association with monsoon rainfall. Large AODs (α~1.4) were observed during the rain-deficit summer monsoon season (SMS) of 2002, which persisted for more than six months. Enhancement in AODs during SMS 2002 was ~0.15 (at 500nm), compared to 2001 and 2003.