Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
Aviation and the Global Atmosphere
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4.2.3. Model Results for Subsonic Aircraft Emissions
4.2.3.1. Ozone Perturbation
Figure 4-1 presents annual zonal average increases of O3 volume mixing ratios caused
by aircraft NOx emissions predicted by the six models for the year 2015. As this figure
shows, the models treat the tropopause significantly differently, which leads to
qualitatively different O3 distributions and calculated O3 perturbations near the
tropopause. The UiO model calculates a maximum increase of O 3 of about 9 ppbv
around 40-80°N at an elevation of 10-13 km. Throughout most of the Northern
Hemisphere, increases larger than 1 ppbv are calculated. The IMAGES/BISA and
HARVARD models calculate somewhat smaller peak perturbations of about 7 ppbv. In
contrast, the Tm3 /KNMI and the UKMO models calculate maximum changes of about 11
ppbv. The UKMO model computes large increases up to the 16-km level, probably as a
result of relatively large vertical exchange rates in the vicinity of the tropopause. In
contrast to the other models, the ECHAm3 /CHEM model predicts the highest O3 perturbations in the Northern Hemisphere and Southern Hemisphere LS. Tropospheric
changes are smaller than in the other models, however. The difference may be partly a
result of the length of the ECHAm3 /CHEM model run. This model has a representation
of the stratosphere and reported results from the average of the last 10 years of a 15year
simulation-long enough to propagate aircraft emissions and O3 perturbation in the
Northern Hemisphere to the Southern Hemisphere (via the stratosphere). The other 3-D
models do not account for such stratospheric transport processes because they
constrain O 3 concentrations in their upper model levels: They fix their upper model layer
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