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

Measurements of aerosol optical depth are presented in the spectral interval 0.40-1.10 mu m, which includes the most transparent region of the solar spectrum and the near infrared. The measurements were obtained by a grating spectrometer with a resolution approximate to 0.5 nm during the 1994 summer season at a mountain site (about 850 m above sea level) in the South of Italy. Spectral regions free from gas absorption features have been singled out and used to retrieve the aerosol columnar size distribution. Inversions have been performed by using the Phillips-Twomey inversion method along with a chi(2) criterion which allows one to choose a suitable value for the regularization parameter. The 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 transformations which are well correlated with relative humidity.