Contrails and Aviation-induced Cirrus Clouds
In 1993, a study of toxic emissions at Chicago's Midway Airport revealed that arriving and departing planes released more pollutants than the industrial pollution sources in the surrounding 16-square-mile area. A more recent study at London's Heathrow airport showed that aircraft contributed between 16 and 35 percent of ground level NOx concentrations.
Because of local concerns about the gases exhausted by airplanes, the expansion plans of several U.S. airports�Atlanta, Boston, Chicago, Houston, Los Angeles, New York, Philadelphia, Phoenix, and Washington�have been stopped. Internationally, NOx emission limits set by the ICAO could result in strategies to limit air traffic, such as per flight emissions fees and curfews. Environmental concerns together with the prediction that world air traffic will grow 5 percent annually for the next decade have made reducing aircraft NOx emissions a priority.