SPECTRAL CHARACTERISTICS OF URBAN AEROSOLS AND THEIR ASSOCIATION WITHRELATIVE-HUMIDITY

Multi-spectral extinction measurements made with co-located high-spect ral resolution radiometer (spectroradiometer) and sunphotometer at the Indian Institute of Tropical Meteorology (IITM), Pune (18 degrees 32' N, 73 degrees 51'E, 559 m AMSL) on 188 cloud-free days between March 1 993 and May 1995 are presented. The observed aerosol optical size spec trum was approximated by a composite power-law distribution function. The seasonal mean size distributions, inferred from both the radiomete rs, exhibit a power-law type distribution with different exponents cha nging at an intermediate size. The mean Junge size exponents (<(nu)ove r bar>(1) and <(nu)over bar>(2)) and switching radius ((r) over bar(0) ) obtained with spectroradiometer are found to be in good agreement wi th those obtained with sunphotometer. The relationships among aerosol optical depths and derived size distributions, and meteorological para meters (height-integrated) are discussed. (C) 1997 Elsevier Science B. V.