Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
NO speeds the catalytic oxidation rate of CO and reduces the destruction rate of ozone by HO x and halogens (primarily in the stratosphere). In this context, it is
important to note that the conventional troposphere-stratosphere boundary (i.e., the tropopause), reflecting important changes in atmospheric dynamics, does not
coincide with the separation between net positive and negative NO x -induced changes in ozone (see right panel of Figure 2-2). This distinction is important when
considering future aviation scenarios that include a significant supersonic component.
The actual quantitative change in ozone from present aircraft operation is very sensitive to the meteorology of this region of the atmosphere; longer residence times will
lead to larger NO x increases and therefore higher ozone. As a result, only coupled chemical and dynamic models can estimate how large an increase is expected. To
accurately predict the perturbation, these models must accurately describe the background NO x concentration, the magnitude of the aircraft-induced NO x perturbation,
the sources of HO x in this region of the atmosphere, and the meteorology. Finally, because ozone itself is relatively long-lived in the UT and LS, its concentration is
strongly influenced by transport (as discussed in Section 2.1.1.3.3). The transport of ozone between different regions of the atmosphere significantly confounds
attempts to assign causality to local ozone trends. As described in Section 2.1.3, the production of particulates and aircraft-induced formation of clouds may be
important for ozone. Chemical processes occurring in aerosols and on ice clouds may lead to increases in chlorine radical abundance in the stratosphere and suppress
NO x throughout the region.
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