 Air quality around airports is another major issue and a 2006 study found that levels of nitrogen dioxide exceeds EU guidelines at more than two thirds of airports surveyed . Whilst aircraft contribute to the problem the study states that " … cars , buses and taxis ferrying passengers to and from these sites are dominant sources of pollution . " Birmingham airport dismissed the findings , asserting that the results were skewed by M42 motorway traffic unrelated to the airport , whilst studies at Southampton Airport attribute 5 @.@ 55 per cent of total pollutants to airport activities , the majority of the remainder being generated by non @-@ airport related road traffic . The government recognises Heathrow as the only UK airport where national and European air quality limits are being exceeded . 
