Data from five continuous years (1984 to 1989) at Teide Observatory (Iza na, Tenerife, Canary Islands) obtained with a full-disc solar multichannel photometer devoted to the detection of solar intensity oscillations has now been used for a detailed study of the extinction coefficient behaviour at several wavelengths (from 450 nm to 870 nm) and aerosol size distributions under different atmospheric conditions. From this study we conclude that an extinction coefficient around 0.075 mag airmass(-1) at 680 nm constitutes the borderline between clear days and dusty days affected by the occasional presence of wind-blown Saharan dust. In the former the extinction can vary between 0.04 and 0.07 mag airmass(-1) (at 680 nm) and in the latter between 0.075 and 0.8 mag airmass(-1) (at 680 nm). Moreover the dust produces a grey effect in the wavelength range analysed in this work. From the extinction coefficients we use inversion methods to compute the particle size distribution in both atmospheric conditions. Approximately, the extinction on clear and dusty days is produced by aerosol particles with radius between 40 and 120 nm and between 120 and 3000 nm, respectively.