Abstract
The horizontal attenuation of ultraviolet light by the air near the ground was determined as a continuous function of wavelength from 2300 to 4600 A. Measurements were made by means of photographic spectrophotometry on seventy-eight nights during 1949 at Pasadena, California, and also on three nights during 1950 at Washington, D. C. The results are given in the form of a table of attenuation coefficients (km−1) at selected wavelengths and in the form of representative spectral attenuation curves for conditions ranging from fog to exceptionally clear air. Except for weak oxygen absorption bands between 2421 and 2700 A, the attenuation coefficient was found to vary quite smoothly (though differently) with wavelength on all nights. Air pollutants, though frequently present, were not spectroscopically identified except for sulfur dioxide, which was encountered in measurable concentration in Washington. Ozone concentrations could be estimated from a few spectra obtained in exceptionally clear weather.
© 1955 Optical Society of America
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