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611233 
Journal Article 
The urban "nitrogen dioxide (NO2) problem" - What is the influence of direct vehicular emissions? 
Kurtenbach, R; Becker, KH; Bruckmann, P; Kleffmann, J; Niedojadlo, A; Wiesen, P 
2009 
Yes 
Gefahrstoffe, Reinhaltung der Luft / Air Quality Control
ISSN: 0949-8036
EISSN: 1436-4891 
69 
4 
146-149 
WOS:000265971800005 
The decreasing NOx-concentrations at urban measurement stations in Germany is in agreement with the reduction of NOx emissions from vehicular traffic. However, the measured NO2 concentrations are stagnating nationwide. In 2007, at more than the half of the urban measurement stations in Germany annual mean values for NO2 exceeded the Europe wide limit value of 40 mu g/m(3) (20 ppb) NO2 which will be effective form 2010. The observed trend of the airborne NO2 concentrations has different reasons. The contribution of primary emitted NO2 from road traffic has increased during the past leading to increasing NO2/NOx emission ratios. Furthermore, the high contribution of the secondary NO2, mainly limited by ozone concentration and photochemistry, is leading to high NO2 concentrations. Based on the results from the present study, the increased direct NO2/NOx emission ratio can only explain a minor fraction of the observed high airborne NO2 concentration, since secondary NO2 formation is mainly determining the NO2 concentration in the city centres. Accordingly, a reduction of primary NO2 emissions, due to improved exhaust gas treatment, will not have a strong influence on urban NO2 levels. A further strong reduction of the NOx emission, in particular from vehicular traffic, is necessary in order to meet the annual mean limit value for NO2 of about 20 ppb from 2010.