Only recently, the scientific community has become to see air pollution by subsonic aircraft as potentially a serious threat to the environment.
This may be illustrated by the fact that in the most recent bi-annual assessment of the ozone layer of the WMO (WMO 1991), the topic has for the first time been taken into account in a separate section.
W Fransen. Atmospheric effects of high-flying subsonic aircraft : a catalogue of perturbing influences
KNMI number: WR-94-03, Year: 1994, Pages: 0