20% of NO2 air pollution in Barcelona is due to excess diesel emissions

27 January 2021
CALIOPE-Urban, a new high-resolution air quality modeling tool, reveals the impact of the failure of diesel vehicles to meet European emission limits in real driving conditions in the streets of Barcelona.

Scientists from the Barcelona Supercomputing Center (BSC) have published a study that shows that 20% of nitrogen dioxide (NO2) concentrations in Barcelona, coming mainly from vehicles that circulate in Barcelona, ​​are due to diesel cars and vans that largely exceed the European Union legal emission limits.

Previous studies had indeed revealed that the vast majority of diesel vehicle models manufactured between 2000 and 2018 significantly exceeded the legal nitrogen oxides (NOX) emission limits.

The article “On the impact of excess diesel NOX emissions upon NO2 pollution in a compact city”, published today in Environmental Research Letters, uses CALIOPE-Urban, a new high-resolution tool created at the Barcelona Supercomputing Center, to calculate the impact of these excess emissions across the streets of Barcelona. The research shows that lower-resolution modeling studies had underestimated this impact.

Jaime Benavides, a researcher in the Atmospheric Composition group and creator of the CALIOPE-Urban air quality modeling tool, explains that “exposure to nitrogen dioxide, which is a potentially harmful pollutant for our health, is not homogeneous across city streets. For this reason, using higher resolution models, that is, on a street scale, helps us to better understand the real impact of the exposure of citizens to this dangerous pollutant”.

Another conclusion of the research is that, without the excess emissions of diesel cars and vans, the number of citizens exposed to unhealthy levels of NO2 concentrations in Barcelona would be 59%. However, because of this excess, the figure rises to 70%.

“We have extrapolated the results and we have verified that, even if there had never been excess emissions from diesel cars and vans, Barcelona would continue to exceed the legal limits for NO2 air pollution at measuring stations exposed to traffic. This seems to indicate that, in addition to moving around in cleaner cars, it is necessary to drastically reduce traffic in general in order to breathe healthier air”, highlights Jaime Benavides.

This is the first time that such a comprehensive study has been carried out, at street level, on the impact of excess diesel emissions across an entire city. Only in Berlin has its impact been previously studied at this level of detail. It was calculated only in specific areas that were exposed to traffic and results were very similar to that of the BSC study. Since 2019, the German capital only allows the entry of recent diesel cars (the so-called Euro 6) into some areas of the city.

Barcelona is the city chosen for this study because it is one of the European cities with the highest density of vehicles (about 6,000 cars per km2), even ahead of Madrid or Paris (with 1,500 - 2,000 vehicles per km2). In addition, the city has a very high number of diesel cars, which represent 65% of the total, as in most European cities. Another reason why Barcelona has been chosen is because of its high air pollution levels, which systematically exceed the legal threshold established by both Europe and the World Health Organization (WHO) for NO2 (nitrogen dioxide) concentrations, which is 40 micrograms per cubic meter on a yearly average.