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Residents of large European cities are exposed to NO₂ concentrations that often exceed the established air quality standards. Diesel cars have been identified as a major contributor to this situation; yet, it remains unclear to which levels the NO_X emissions of diesel cars have to decrease to effectively mitigate urban NO₂ pollution across Europe. Here, we take a continental perspective and model urban NO₂ pollution in a generic street canyon of 8 major European cities for various NO_X emission scenarios. We find that a reduction in the on-road NO_X emissions of diesel cars to the Euro 6 level can in general decrease the regional and urban NO₂ concentrations and thereby the frequency of exceedances of the NO₂ air quality standard. High NO₂ fractions in the NO_X emissions of diesel cars tend to increase the urban NO₂ concentrations only in proximity of intense road traffic typically found on artery roads in large …