In order to protect human health and the environment, the Council of the European Union drew up a directive with air quality standards in April 1999. With the Statutory Order on target and limit values for the level of certain air pollutants the Danish government transposed this EU directive into national legislation. The directive establishes limit values for pollutant concentration in order to maintain the air quality. Accordingly, the limit value for particulate matter was set at 50 micrograms per cubic meter of air, which may be exceeded on a maximum of 35 days a year. The average annual value for nitrogen dioxide was set at 40µg/m3. The EU directive obliges cities and municipalities to draw up action plans for air pollution control. The Danish Ministry of Environment prepared technical plans in 2012 showing how to fulfill the NO2 limit value (PM limit values are fulfilled), but the Danish Ministry of Finance decided not to approve the plans. But some measures for reducing traffic emissions with PM have been implemented earlier.
Heavy-duty diesel-powered vehicles were responsible for approximately half of the harmful particle emission in the largest cities in Denmark. In order to address this problem, the Danish Parliament passed in 2006 an act allowing the four largest cities in Denmark to introduce low emission zones. The LEZ encompass diesel-powered trucks and busses weighting over 3,500 kg. The heavy-duty vehicles must either meet the Euro 4 standard (or newer) or be retrofitted with particle filter. Heavy-duty vehicles must have a low emission zone label in the windshield. Low emission zone are implemented in Copenhagen (incl. Frederiksberg), Aarhus, Odense and Aalborg.
If the limit values are not met due to the lack of regulations or measures, citizens may legally enforce the implementation of such measures. If the city or municipality do not take any action to improve the situation within a reasonable period, individuals affected may sue the authority that is responsible for drawing up such a plan. Anybody living or working most of their time in a polluted environment may take legal action. This means not only residents but also physicians in medical practices on busy roads, for example, or educators in kindergartens or parents for their children, if the kindergarten is located in an area heavily affected by particulate matters or NO2.