In urban Seattle, simultaneous measurements were made of backscatter using a ruby laser radar and of the scattering portion of extinction using an integrating nephelometer. Both instruments were calibrated allowing separation of molecular and aerosol contributions to the two scatter coefficients. During the period of the experiment, backscatter and the scattering portion of extinction were well correlated at relative humidities less than 70%. For the aerosol, the ratio of backscatter to the scattering portion of extinction was only one-third that predicted from spherical particle Mie calculations for a power law size distribution aerosol.
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