NO2 photolysis frequencies in street canyons P. Koepke1, M. Garhammer1, M. Hess1, and E.-P. Roeth2 1L-M University Munich, Meteorological Institute, Theresienstr. 37, 80333 Munich, Germany 2Research Centre Jülich GmbH, ICG1-Stratosphere, Leo Brandt Strasse, 52425 Jülich, Germany
Abstract. Photolysis frequencies for NO2 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 RJ 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 NO2 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 NO2
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
Citation: Koepke, P., Garhammer, M., Hess, M., and Roeth, E.-P.: NO2 photolysis frequencies in street canyons, Atmos. Chem. Phys., 10, 7457-7466, doi:10.5194/acp-10-7457-2010, 2010.