Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
the models' credibility in assessing aircraft emissions is the identification and quantification of background NO x levels and sources. Recent HO x measurements allow
for a much better understanding of ozone production in the UT, and these measurements have shown that additional HO x sources are necessary to explain the
observations. Moreover, these additional HO x sources cause the sensitivity of ozone production from NO x emissions to be higher than previously thought.
Much less confidence is attached to our understanding of the effects of NO x emissions in the lowermost stratosphere and aerosol emissions in the troposphere and
stratosphere. The available data suggest that these effects are smaller than (and, in the case of aerosols, of opposite sign) those of NO x emissions in the UT (see
Figure 2-8).
Based on our model predictions, the impact of present subsonic NOx emissions on ozone is well within the range of interannual variability of ozone concentrations in
the UT as measured with ozonesondes. Furthermore, expressed as a decadal trend, the impact of subsonic NOx emissions on upper tropospheric and lower
stratospheric ozone is smaller than or comparable to the span of confidence limits in the ozone trend analysis for mid-latitude stations. Finally, we note that aircraft
NOx emissions should lead to decreased CH4 concentrations; however, any impact should be undetectable in the CH4 record.
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