No one can argue that air pollution has a negative effect on human health. The World Health Organization estimates that every year, 7 million people die as a result of air pollution, which is why the European Union has set limits on air pollutants. The concentration of nitrogen dioxide (NO2) in the air may not exceed an annual average of 40 micrograms per cubic metre, according to the EU Air Quality Directive. Measuring stations in all EU countries monitor compliance with this limit.

Dubious honour: First place for London and Saint-Denis The highest pollution level in the EU was measured in London, at the Marylebone Road station, in 2017, followed closely by a station in Saint-Denis, France. In these spots, the EU limit of 40 μg/m³ was exceeded by more than double. Stations with significantly higher NO2 levels are also found in Italy and Germany. In general, nitrogen dioxide levels are higher in cities, as pollution is primarily determined by local emission sources such as traffic or industry. In contract, the levels in more rural areas are significantly reduced.

Different measuring stations Air quality measuring stations differ from one another and can be classified. One way they can be sorted is by station type - transport, industry or background. They are also placed into one of three zones: urban, suburban or rural. The combination of station type and zone is called a pollution regime by experts. For example, a measuring station classified under the rural background regime can be found far away from emission sources. According to European Environment Agency standards, large emission sources such as cities, power plants or highways should be 10-50 kilometres away from a measuring station. For smaller sources, such as household heating systems or streets, a distance of 100-500 metres is required.

In contrast, urban background stations should represent the average pollution level in urban areas. The stations are, however, never in direct proximity to strong emission sources such as road traffic or industrial areas. The European Environment Agency recommends locations where no more than 2,500 vehicles per day drive within a radius of 50 meters, as well as a minimum distance of 50 metres to domestic heating systems. Traffic stations are in close proximity to streets and depict inner-city hotspots.

Differences in the amount of measuring stations within the EU In some countries, only a few measuring stations monitor air quality, making it hardly possible to get an adequate picture of the concentration of air pollutants in an area, since the concentration level is heavily dependent on local conditions and meteorological events. Researchers therefore call for more measurements to be taken of air pollution through measuring stations.