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 vastly exceed the European Union legal emission limits.

Previous studies revealed that most diesel vehicle models manufactured between 2000 and 2018 significantly exceeded the legal nitrogen oxides (NO_X) emission limits.

The article “On the impact of excess diesel NO_X 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 modelling studies underestimated this impact.

Jaime Benavides, a researcher in the Atmospheric Composition group and creator of the CALIOPE-Urban air quality modelling 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 better understand the real impact of citizens' exposure 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 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 indicates that, in addition to moving around in cleaner cars, it is necessary to reduce traffic in general to breathe healthier air drastically,” highlights Jaime Benavides.

This is the first time 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 exposed to traffic, and the results were 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 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, representing 65% of the total, as in most European cities. Another reason Barcelona has been chosen is its high air pollution levels, which systematically exceed the legal threshold established by Europe and the World Health Organization (WHO) for NO₂ (nitrogen dioxide) concentrations, which is 40 micrograms per cubic meter on a yearly average.