Nitrogen dioxide photolysis in the Los Angeles atmosphere

Atmospheric measurements of k/sub 1/, the rate of NO/sub 2/ photolysis, were made in El Monte, Calif., by use of a tubular quartz reactor to measure directly the conversion of NO/sub 2/ to NO in an N/sub 2/ atmosphere. A least-squares treatment of the data from September 1975 resulted in the following empirical relationships for predicting k/sub 1/ from standard uv radiometric data. 0/sup 0/ < Solar zenith angle < 40/sup 0/:k/sub 1/ (min/sup -1/) = 0.079 (1/cos z) + 0.002 x radiometric uv (mW/cm/sup 2/); 40/sup 0/ < solar zenith angle < 90/sup 0/:k/sub 1/ (min/sup -1/) = 0.16 (1 - cos z) + 0.088 x radiometric uv (mW/cm/sup 2/). Ultraviolet intensities corresponding to k/sub 1/ values greater than 0.4, 0.3, and 0.2 min/sup -1/ can persist for periods of 8, 10, and 12 h, respectively, during the weeks around the summer solstice. Both the high photochemical light intensity observed and its extended time duration indicate that the potential for ozone formation in the atmosphere is greater than utilized in most previous ''smog chamber'' studies. This result suggests that the application of existing smog chamber data in such areas as solvent reactivity may have to be reinterpreted.