Abstract
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 NOX 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 NOX emission scenarios. We find that a reduction in the on-road NOX 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 NOX 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 cities like Paris and London. In cities with a low share of diesel cars in the vehicle fleet such as Athens or a high contribution from the NO2 background to the urban NO2 pollution such as Krakow, measures addressing heavy-duty vehicles, and the manufacturing, energy, and mining industry are necessary to decrease urban air pollution. We regard our model results as robust albeit subject to uncertainty resulting from the application of a generic street layout. With small modifications in the input parameters, our model could be used to assess the impact of NOX emissions from road transport on NO2 air pollution in any European city.
Highlights
Residents of many larger European cities are still exposed to NO2 concentrations that often exceed the established air quality standards (EEA, 2015)
By applying the set of boundary conditions from Milan to the street grid of Antwerp, we find that the annual average NO2 concentration in Milan exceeds the one in Antwerp by 23 μg/m3 (Table 2)
Benchmarking our results against measurements of actual NO2 concentrations suggests that our modelling approach yields a reliable first-order approximation of the effect of various NOX emission sources on urban NO2 concentrations in European cities
Summary
Residents of many larger European cities are still exposed to NO2 concentrations that often exceed the established air quality standards (EEA, 2015). Policy makers expected the NOX emissions of diesel cars to decrease considerably when introducing more stringent Euro 5 and Euro 6a/b emission limits in 2009 and 2014 (EC, 2012, 2008a,b). Euro 6d-TEMP introduces binding RDE limits with a temporary conformity factor (CF) of 2.1 This means that NOX emissions measured on the road have to be below 80 × 2.1 = 168 mg/ km. Simplified modelling of NO2 pollution in 8 European cities We determine the effect of diesel car NOX emissions and their NO2 fractions on the NO2 air pollution in the following 8 cities: Antwerp, Athens, Barcelona, Krakow, London, Milano, Paris, and Stockholm. The chosen cities (i) comprise major metropolitan areas with a large population, (ii) resemble a wide range of geographic and climatic conditions across Europe, and (iii) are frequently exposed to elevated NO2 pollution levels (EEA, 2013)
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