A STUDY OF THE AEROSOL OF SANTIAGO-DE-CHILE .3. LIGHT-ABSORPTION MEASUREMENTS

The light absorption coefficient of the aerosol of Santiago de Chile h as been measured by means of the integrating plate method. Values rang ing between 0.01 and 0.2 km(-1) have been found. Variations of the abs orption coefficient by a factor of 8 within a few hours have frequentl y been found and have their causes in the specific meteorology of the Santiago air basin. In the summer a minimum occurs between 1 and 4 a.m . and a maximum between 8 and 10 a.m., whereas in the winter a maximum is found during the night and minimum values are in the afternoon wit h a smaller amplitude. Similar variations of the light absorption coef ficient have been found also inside uninhabited rooms, since the aeros ol was transported there almost without any losses. The daily pattern is similar but delayed and has a lower mean value and amplitude. When converting the light absorption to mass of black carbon, concentration s of elemental carbon of 1.3-25 mu g m(-3) were obtained. This is simi lar to other large cities, where a considerable part of the mobile sou rces are equipped with diesel motors. The light absorption contributes to about 15% of the light extinction of the aerosol, and considering an equal scattering of the soot particles, the contribution of soot to light attenuation in the atmosphere is about 30%. The single scatteri ng albedo of the aerosol is 0.85, thus the heating effect of the absor ption dominates. The light absorption coefficient is wavelength depend ent with an average relationship of sigma(a) = k (lambda/lambda(0)) (- x), the exponent being alpha = 0.92. The exponent of the wavelength de pendence of the extinction coefficient of the aerosol was 1.22. (C) 19 97 Elsevier Science Ltd.