Spectral characteristics of urban aerosols and their association with relative humidity

Multi-spectral extinction measurements made with co-located high-spectral resolution radiometer (spectroradiometer) and sunphotometer at the Indian Institute of Tropical Meteorology (IITM), Pune (18°32′N, 73°5′E, 559 m AMSL) on 188 cloud-free days between March 1993 and May 1995 are presented. The observed aerosol optical size spectrum was approximatd by a composite power-law distribution function. The seasonal mean size distributions, inferred from both the radiometers, exhibit a power-law type distribution with different exponents changing at an intermediate size. The mean Junge size exponents ( ν 1 and ν 2 ) and switching radius ( r 0) obtained with spectroradiometer are found to be in good agreement with those obtained with sunphotometer. The relationships among aerosol optical depths and derived size distributions, and meteorological parameters (height-integrated) are discussed.