Temporal Characteristics of Aerosol Optical Depths and Size Distribution at Visakhapatnam, India

Abstract

Aerosol spectral optical depths and size distribution derived from the direct solar flux measurements at nine discrete wavelengths in the visible and near IR region for a period of about 10 years exhibit a gradual increase in the aerosol spectral optical depths from 1994-1997. There was a very large increase in the optical depths during 1991 after the volcanic eruption of Mt. Pinatubo and its effect persisted until 1993-94. The size distribution during 1988-1996 (excluding 1991, 1992, and 1993) remained bimodal in nature with an increase in the small particle number density with year. The aerosol optical depths and size distribu tions at Visakhapatnam also show some short period changes, characterizing the high sensitivity of the coastal urban aerosol system to the mesoscale weather. The observed features have been explained on the basis of the aerosol genesis based on local sources, sinks, and the prevailing weather.