Impact of passenger car NOx emissions and NO2 fractions on urban NO2 pollution – Scenario analysis for the city of Antwerp, Belgium

2016 
Abstract The annual NO 2 concentrations in many European cities exceed the established air quality standard. This situation is mainly caused by Diesel cars whose NO x emissions are higher on the road than during type approval in the laboratory. Moreover, the fraction of NO 2 in the NO x emissions of modern diesel cars appears to have increased as compared to previous models. In this paper, we assess 1) to which level the distance-specific NO x emissions of Diesel cars should be reduced to meet established air quality standards and 2) if it would be useful to introduce a complementary NO 2 emissions limit. We develop a NO 2 pollution model that accounts in an analysis of 9 emission scenarios for changes in both, the urban background NO 2 concentrations and the local NO 2 emissions at street level. We apply this model to the city of Antwerp, Belgium. The results suggest that a reduction in NO x emissions decreases the regional and urban NO 2 background concentration; high NO 2 fractions increase the ambient NO 2 concentrations only in close spatial proximity to the emission source. In a busy access road to the city centre, the average NO 2 concentration can be reduced by 23% if Diesel cars emitted 0.35 g NO x /km instead of the current 0.62 g NO x /km. Reductions of 45% are possible if the NO X emissions of Diesel cars decreased to the level of gasoline cars (0.03 g NO x /km). Our findings suggest that the Real-Driving Emissions (RDE) test procedure can solve the problem of NO 2 exceedances in cities if it reduced the on-road NO x emissions of diesel cars to the permissible limit of 0.08 g/km. The implementation of a complementary NO 2 emissions limit may then become superfluous. If Diesel cars continue to exceed by several factors their NO x emissions limit on the road, a shift of the vehicle fleet to gasoline cars may be necessary to solve persisting air quality problems.
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