Subsonic jet aircraft and stratospheric pollution

A significant number of thepresent long-range subsonic jet aircraft flights are in the stratosphere. Based on fuel consumption, an equivalent of 107 SST aircraft (Concorde) have been flying in the stratosphere each year from 1960 to 1970 (620 equivalent SST in 1990). Subsonic jets in 1990 will burn about 1.6 times as much fuel in the stratosphere as SST aircraft. Based on a Concorde emission index of 12.5 for NO, the amount of NO_x emitted by subsonic jets in the stratosphere from 1960 to 1970 is equivalent to an average of 20 Concordes (444 Concordes in 1990). Available information concerning mixing and transport in the atmosphere indicates that both subsonic jets and the SST will fly in the same atmospheric environment in the upper troposphere and lower stratosphere insofar as dissipation of their exhaust pollutants is concerned. The tropopause is not an effective barrier to mixing of stratospheric and tropospheric air. Many processes contribute to mixing in the lower stratosphere where the residence time of contaminants is of the order of months instead of years.