Driving ban for diesel-powered vehicles in major cities: an appropriate penalty for exceeding the limit value for nitrogen dioxide?

To protect the general population from adverse health effects, Germany set a limit value of 40 μg/m³ for the annual mean exposure to nitrogen dioxide (NO2) based on WHO’s air-quality guidelines and in accordance with the European directives. Since diesel-powered vehicles are regarded as the main traffic-related source of nitrogen oxides, driving bans for inner-city areas in many large German cities such as Hamburg, Munich, and Stuttgart are the subject of intense debate.