ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-10-7457-2010 NO<sub>2</sub> photolysis frequencies in street canyons Koepke P. 1 Garhammer M. 1 Hess M. 1 Roeth E.-P. 2 L-M University Munich, Meteorological Institute, Theresienstr. 37, 80333 Munich, Germany Research Centre Jülich GmbH, ICG1-Stratosphere, Leo Brandt Strasse, 52425 Jülich, Germany 10 08 2010 10 15 7457 7466 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/10/7457/2010/acp-10-7457-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/10/7457/2010/acp-10-7457-2010.pdf

Photolysis frequencies for NO<sub>2</sub> are modeled for the conditions in urban streets, which are taken into account as canyons with variable height and width. The effect of a street canyon is presented with absolute values and as a ratio <i>RJ</i> of the photolysis frequency within the street compared to that with free horizon. This allows further use of the existing photolysis parameterizations. Values are presented for variable solar elevation and azimuth angles, varying atmospheric conditions and different street properties. The NO<sub>2</sub> photolysis frequency in a street depends strongly on the relative width of the street and its orientation towards the sun. Averaged over atmospheric conditions and street orientation, the NO<sub>2</sub> photolysis frequency is reduced in comparison with the values for free horizon: to less than 20% for narrow skyscraper streets, to about 40% for typical urban streets, and only to about 80% for garden streets. A parameterization with the global solar irradiance is given for the averaged <i>RJ</i> values.

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