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

Highlights

• We model street canyon NO₂ for different diesel car NO_x emissions and NO₂ fractions.

• We consider the changes in European, regional and local street canyon emissions.

• Air quality would benefit from compliance of diesel cars with Euro 6 under real-driving conditions.

• High NO₂ fractions impact the exceedance of the hourly limit value of 200 μg/m³.

Abstract

The annual NO₂ 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 NO₂ 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 NO₂ emissions limit. We develop a NO₂ pollution model that accounts in an analysis of 9 emission scenarios for changes in both, the urban background NO₂ concentrations and the local NO₂ 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 NO₂ background concentration; high NO₂ fractions increase the ambient NO₂ concentrations only in close spatial proximity to the emission source. In a busy access road to the city centre, the average NO₂ 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 NO₂ 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 NO₂ 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.