Airport operators are expected to undertake appropriate health impact assessments when bringing forward any expansion plans. “Air Quality Assessments Supporting the Government's White Paper” was published alongside “The Future of Air Transport” in December 2003; this covers Heathrow, Gatwick, Stansted and Birmingham airports. The document is on the internet at http://www.dft.gov.uk/about/strategy/whitepapers/air/docs/airqualityassessmentssupport5665.
Future levels of ambient air quality are being studied as part of the Project for the Sustainable Development of Heathrow. The Air Quality Technical Report, published in July 2006 found that the key pollutants are nitrogen dioxide (NO2), nitrogen oxides (NOx), and particulate matter (PM10), for which there are EU limit values aimed at reducing harmful effects on human health and the environment as a whole.