AEROSOL SPECTRAL OPTICAL DEPTHS AND TYPICAL SIZE DISTRIBUTIONS AT A COASTAL URBAN LOCATION IN INDIA

The ground-reaching direct solar flux measurements at 9 different wave lengths in the visible and near infrared region using a ground based m ultiwavelength radiometer have been used to study the spectral and tem poral variation of aerosol optical depths and size distribution over V isakhapatnam (17.7 degrees N, 83.3 degrees E), a coastal industrial lo cation on the east coast of India. The aerosol optical depths exhibit a typical spectral variation with summer maxima at all the 9 wavelengt hs. The inversion of the spectral optical depths following the constra ined linear inversion algorithms yielded a typical bi-modal aerosol si ze distribution at Visakhapatnam with the primary mode centered around 0.1 mu m and the secondary mode around 0.8 mu m. The observed feature s, when examined along with the mesoscale meteorological data have ind icated a strong control of the local sources and sinks on the aerosol populations of different sizes.