Evaluation of the atmospheric content of particulate mass from visibility observations

Reliable estimates of the atmospheric mass content of particulate matter can be obtained from visibility observations if they are made by (1) following the criteria defined by Horvath (1971), and (2) evaluating attenuation characteristics by Rayleigh scattering, as well as absorption by atmospheric gases such as ozone and nitrogen dioxide, using data related to the variation of the maximum perception wavelength. In addition, use may be made of mass extinction coefficients obtained from particle models which present realistic features. It is noted that attention must be given to the relative humidity conditions at ground level and to the spectral features of atmospheric extinction, as well as to the origin of the air mass.