| Within the EU-project TRADEOFF, the impact of NOx (=NO+NO2) emissions from subsonic aviation upon the chemical composition of the
atmosphere has been calculated with focus on changes in reactive nitrogen
and ozone. We apply a 3-D chemical transport model that includes
comprehensive chemistry for both the troposphere and the stratosphere and
uses various aircraft emission scenarios developed during TRADEOFF for the
year 2000. The environmental effects of enhanced air traffic along polar
routes and of possible changes in cruising altitude are investigated, taking
into account effects of flight route changes on fuel consumption and
emissions.
In a reference case including both civil and military aircraft the model
predicts aircraft-induced maximum increases of zonal-mean NOy (=total reactive nitrogen) between 156 pptv (August) and 322 pptv (May) in the
tropopause region of the Northern Hemisphere. Resulting maximum increases in
zonal-mean ozone vary between 3.1 ppbv in September and 7.7 ppbv in June.
Enhanced use of polar routes implies substantially larger zonal-mean ozone
increases in high Northern latitudes during summer, while the effect is
negligible in winter.
Lowering the flight altitude leads to smaller ozone increases in the lower
stratosphere and upper troposphere, and to larger ozone increases at
altitudes below. Regarding total ozone change, the degree of cancellation
between these two effects depends on latitude and season, but annually and
globally averaged the contribution from higher altitudes dominates, mainly
due to washout of NOy in the troposphere, which weakens the
tropospheric increase.
Raising flight altitudes increases the ozone burden both in the troposphere
and the lower stratosphere, primarily due to a more efficient accumulation
of pollutants in the stratosphere. |