The Effects Of Military Aircraft In The 20th Century

Introduction

During the 20th century? the world's transportation system has changed dramatically with the gradual emergence of a large fleet of commercial aircraft. Today? thousands of aircraft carry each year several millions of passengers all over the world. The size of the world's fleet has increased constantly over the past decades and is expected to do so in the future. As a result of improvements in the aircraft technology? the nature of the fleet has evolved and will change further in the future (Appleman? 14-20).

Today? the major fraction of the commercial fleet is provided by jet aircraft which cruise for the most part in the upper troposphere and lower stratosphere (typically 9-12 km altitude) at subsonic speed. Since the early 1970s? however? a small European fleet of 13 Concorde aircraft have been in commercial operation; these aircraft fly supersonically at cruising altitudes of 16.5 km. In the future? this fleet might expand with new aircraft operating at even higher levels (17-22 km) (Appleman? 14-20).

In spite of substantial improvements in engine technology? aircraft operations result in the emission of gaseous and particle effluents? including carbon dioxide? water? hydrocarbons? carbon monoxide? nitrogen oxides? sulphur? soot? etc. In the early 1970s? Crutzen (1971) recognised the role played by the nitrogen oxides in the destruction of stratospheric ozone? and Johnston? 1971 H.S. Johnston? Reduction of stratospheric ozone by nitrogen oxides catalysts from supersonic transport exhaust? Science 173 (pp. 517-522.) suggested that the projected fleet of supersonic aircraft? which would release large amounts of NOx? had the potential to destroy large amounts of stratospheric ozone? and hence to produce a major environmental threat (Appleman? 14-20). Studies conducted in the 1970s within the U.S. Climatic Impact Assessment Program (CIAP)? the French Comité sur les Conséquences des Vols Stratosphériques (COVOS)? and the British Committee on the Meteorological Effects of Stratospheric Aircraft? attempted to quantify these effects. Our understanding of the chemical and dynamical processes occurring in the stratosphere has? however? improved so dramatically over the last decades that the conclusions reached 20 years ago are no longer fully valid and need to be reconsidered (Appenzeller? 15?078).

Since the late 1980s? concern has been expressed over the atmospheric impact of the current (and future) fleet of subsonic aircraft. Assessments performed within WMO/UNEP revealed that the state of knowledge was inadequate to assess the impact of aviation emissions conclusively (Appenzeller? 15?078). Therefore several national and international projects were initiated in Europe (see e.g. Held? 1990; Schumann? 1990; Johnson et al.? 1992; Beck et al.? 1992; ANAE? 1994; Deutscher Bundestag? 1994; ANCAT? 1995; Gardner et al.? 1997a; Schumann? 1997? etc.). Starting in 1992? scientific investigations were carried out under the sponsorship of the European Commission (EC. Similar initiatives have taken place in the United States primarily within the Atmospheric Effects of Aviation Project (AEAP) sponsored by NASA. The AEAP's Subsonic Assessment (SASS) project is assessing the atmospheric effects of current and future world fleets of subsonic aircraft. Both European and American programmes have highlighted our ...