Tropospheric NO2

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Abstract
Optical absorption measurements show the vertical column abundance of NO2 in the troposphere to be less than 3 × 1014 cm−2 in the Colorado mountains when urban pollution does not contribute; when it does contribute, the abundance often exceeds 1016 cm−2. Elsewhere in the western hemisphere the clean air limit is below 1015 cm−2; with a 2‐km scale height for NO2 this corresponds to a mixing ratio of 0.2 ppb at the surface. Owing to the uncertain effects of urban pollution, we can make only a very crude estimate of 1015 cm−2 as a suggested mean for the NO2 column abundance in the troposphere over North America. Additional measurements of NO2 production during electrical storms suggest that lightning strokes, not corona discharge, are by far the dominant source.
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