The European Commission has sent warning letters to ten EU Member States informing them that they have failed to comply with European legislation establishing limits for the concentration of airborne particles known as PM10. Sources of PM10 particles include motor vehicles, dust from construction sites, landfills and agriculture, industry and wood burning stoves. This action follows requests for information sent by the Commission in July 2008 to Cyprus, Estonia, Germany, Italy, Poland, Portugal, Slovenia, Spain, Sweden and the United Kingdom.

Council Directive 1999/30/EC (the 1999 Directive) gave Member States until 1 January 2005 to reduce exposure levels of PM10 to thresholds set out in that legislation. However, the new Air Quality Directive, Directive 2008/50/EC, allows Member States to request that the Commission grants an extension period to comply with the 1999 Directive. Extensions, which may run until 10 June 2011, are allowed where the Member State can show that its non-compliance relates to factors beyond its direct control. Examples of such factors are transboundary air pollution and climatic conditions.

Article 226 EC authorises the Commission to take legal action against a Member State for failure to meet its obligations. Ultimately, the Commission may take the matter before the European Court of Justice.