Photolysis frequencies for NO2 are modeled for the conditions in urbanstreets, which are taken into account as canyons with variable height andwidth. The effect of a street canyon is presented with absolute values andas a ratio RJ of the photolysis frequency within the street compared to thatwith free horizon. This allows further use of the existing photolysisparameterizations. Values are presented for variable solar elevation andazimuth angles, varying atmospheric conditions and different streetproperties. The NO2 photolysis frequency in a street depends stronglyon the relative width of the street and its orientation towards the sun.Averaged over atmospheric conditions and street orientation, the NO2photolysis frequency is reduced in comparison with the values for freehorizon: to less than 20% for narrow skyscraper streets, to about 40%for typical urban streets, and only to about 80% for garden streets. Aparameterization with the global solar irradiance is given for the averagedRJ values.
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