Fig. 2
Concentration trend of NO2 and PM10 and exceedances of the daily limit value for PM10 at the monitoring station Aachen Wilhelmstraße (DENW207). Figure 2 shows air quality concentrations for PM10 (yellow bars) and NO2 (blue bars) from 2006 (reference year of the air quality plan 2009) to 2017 (latest validated values) at the monitoring station Aachen Wilhelmstraße (EU station code DENW207), which is located at an urban traffic hotspot. It is one of the official stations for EU reporting in Aachen and replaced the former station “Kaiserplatz” (VACC) in 2007. Further monitoring (and modelling) has taken place at other locations in the course of the air quality plan developments in particular (e.g. Bezirksregierung Köln 2018). Figure 2 shows that especially the situation for PM10 has improved, both in terms of the EU (40 μg/m3; yellow dotted line) and stricter WHO (20 μg/m3; grey line) annual mean limit values as well as the EU daily limit value (35 days above 50 μg/m3; orange dotted line/orange bar). However, the limit value for NO2 (40 μg/m3; blue dotted line) is exceeded for more than 10 years without any exemption and led to two revisions of the air quality plan so far (note: earlier exceedances occurred even under consideration of margins of tolerance). Sources: Air quality plans for the city of Aachen (Bezirksregierung Köln 2009, 2015, 2018) and reports for selected years from LANUV 2019; EU and WHO limit values were adapted from EEA 2017