An experimental investigation was carried out to determine possible differences in visible light extinction properties of continental and maritime air. Urban, desert, and oceanic atmospheres were probed by means of a stable photodiode radiometer using direct sunlight as the source. No major differences were found for the three locations. Experimental coefficients generally lie slightly below model data, though significantly higher than would be expected from purely molecular scattering. Day-to-day variations of up to 40% were found to be nearly constant over the entire visible spectrum. Results of similar extinction measurements on thin cirrus clouds show a slight increase in scattering coefficient in going from 4000 Å to 7000 Å wavelength.
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