Headline: What Would "Clean" Diesel Cars Do for Air Quality in Berlin? New Study by IASS Researchers

At present, the EU limit values for nitrogen dioxide (NO₂) concentrations are regularly exceeded in Berlin. How would air quality in the German capital improve if diesel cars were to comply with the emissions standards? Researchers at the IASS have published their findings on this issue in a new study.

Their calculations show that if all diesel passenger cars were to comply with the emission standards recommended by the United States Environmental Protection Agency (EPA), there would be a sharp drop in the likelihood of exceedances occurring. "This is the strictest standard currently. We would already see a significant improvement in air quality if vehicles were to comply with the Euro 5 emissions standard. But given the desire of carmakers to sell their vehicles globally, they should be capable of complying with EPA standards. They would have to invest in research and development to achieve this. Our study shows that this investment would contribute significantly to achieving EU air quality targets. Emissions from Euro 5 light passenger vehicles are currently up to five times higher than the statutory limit value in the EU, while emissions from Euro 6 passenger vehicles are as much as four to twenty times higher," explains lead author Erika von Schneidemesser. Nitrogen dioxide (NO₂) is considered to be harmful to human health and and has been linked to respiratory, heart and circulatory diseases.

Data from 16 air quality monitoring stations in Berlin and an atmospheric chemistry model

In order to establish a reliable data basis, the research team used two independent methods, based on measurements gathered at 16 monitoring stations in Berlin and an atmospheric chemistry model. The monitoring stations provided data for roadside concentrations on NO₂, as well as on the so-called urban background concentration, from stations located at some distance from major sources of air pollution, such as industry or vehicles. The atmospheric chemistry model WRF-Chem was used to provide data on the urban background concentration exclusively. In both cases the background concentration results were very similar, underscoring the robustness of the results.

An annual mean concentration of NO₂ of 51 micrograms per cubic metre (µg m^-3) was measured at the six roadside monitoring stations in Berlin over the course of 2014. This clearly exceeds the EU limit value of 40 µg m^-3. The mean urban background concentration measured was 26 µg m^-3. The researchers used data on emissions of nitrous oxides (NO_x) from a European emissions inventory to calculate the proportion of NO_x emissions from diesel passenger cars. They then estimated the share of NO₂ – to which the EU limit value refers – of overall NO_x emissions.

Emissions below limit values even on busy roads

The researchers' calculations show that diesel passenger vehicles account for 3,500 to 6,500 kilotons of the nearly 25,000 kilotons of annual NO_x emissions in Berlin. If vehicles were to comply with the EPA standards, these emissions would drop to 190 to 355 kilotons. This reduction would have the effect of reducing the annual mean urban background concentration of NO₂ by 1.2 to 2.2 µg m^-3. Under this scenario, the mean value measured at roadside monitoring stations would even drop by 9 to 17 µg m^-3. "Limit value exceedances would occur far less frequently. In light of these very clear impacts, policymakers should compel carmakers to take effective measures, particularly in Germany, where diesel has been heavily promoted," commented von Schneidemesser.

• von Schneidemesser, E., Kuik, F., Mar, K. A., Butler, T. M. (2017 online): Potential reductions in ambient NO₂ concentrations from meeting diesel vehicle emissions standards. - Environmental Research Letters.
  DOI: http://doi.org/10.1088/1748-9326/aa8c84