INVERTING HIGH-SPECTRAL-RESOLUTION AEROSOL OPTICAL DEPTH TO DETERMINETHE SIZE DISTRIBUTION OF ATMOSPHERIC AEROSOL

Measurements of aerosol optical depth are presented in the spectral in terval 0.40-1.10 mu m, which includes the most transparent region of t he solar spectrum and the near infrared. The measurements were obtaine d by a grating spectrometer with a resolution approximate to 0.5 nm du ring the 1994 summer season at a mountain site (about 850 m above sea level) in the South of Italy. Spectral regions free from gas absorptio n features have been singled out and used to retrieve the aerosol colu mnar size distribution. Inversions have been performed by using the Ph illips-Twomey inversion method along with a chi(2) criterion which all ows one to choose a suitable value for the regularization parameter. T he result of the inversions are presented in the particle radius range 0.1 divided by 3 mu m and indicate the presence of a bimodal aerosol with the second mode radius at about 1.0 mu m undergoing transformatio ns which are well correlated with relative humidity.