Evidence of Particulate Extinction in the Near Infrared Spectrum of the Sun

Abstract

The optical thickness a(?) of atmospheric particulate matter has been investigated in a near infrared wavelength interval. The instrument (a monochromator with a Newtonian telescope) was located at 1100 m MSL on the Appennine chain. We found an increase of a(?) by comparison with the Bouger-Lambert law with increasing solar elevation. The distribution of a(?) as a function of wavelength, computed at different times, shows that particulate matter either forms locally in the morning or arrives from over the Po Valley. According to the theory of Deirmendjian condensation of water also occurs on the atmospheric particles.