Multiwavelength sun-photometer calibration corrected on the basis of the spectral features characterizing particulate extinction and nitrogen dioxide absorption

Measurements of the optical thicknesses produced by particulate matter extinction and nitrogen dioxide absorption at window wavelengths in the visible and near-infrared spectral range were taken with four examples of a multiwavelength sun photometer. Evaluations of the vertical content of nitrogen dioxide were made by examining these measurements with a procedure which attempts to separate gaseous absorption from particulate extinction, represented in terms of Ångström’s formula. Moreover, assuming that the vertical content of NO2 and Ångström’s turbidity parameters are given by the average values calculated with this procedure, we obtained a set of useful correction factors for the monochromatic calibration values of the four sun photometers.