Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
Aviation and the Global Atmosphere
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2.2. Impacts of Present Aviation on Atmospheric Composition
2.2.1. Modeling Changes in Atmospheric Ozone from Present Aviation
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Because of the substantial chemical and dynamic differences between the stratosphere and the troposphere, individual atmospheric models have tended to focus on
one or the other of the regions. This separation has worked well in addressing primarily stratospheric issues such as chlorofluorocarbons (CFCs) and tropospheric
issues such as regional pollution. Subsonic aircraft emissions, insofar as they are injected into the interface between the two atmospheric regions, present a
particularly complex modeling challenge. To date, almost all model studies of subsonic aircraft NO x effects have been conducted with models that emphasize
tropospheric chemistry; few contain an explicit representation of stratospheric chemistry. Most of the following discussion will center on those efforts. However, two
models of the stratosphere-the Atmospheric Environmental Research (AER) and Commonwealth Scientific and Industrial Research Organisation (CSIRO) models
used in Chapter 4-have calculated stratospheric ozone responses to 1992 subsonic fleet emissions of NO x . We discuss these results in Section 2.2.1.2 and use them
in conjunction with the tropospheric model results to arrive at a total atmospheric impact of NO x emissions from present subsonic aviation.
Recognition of the importance of heterogeneous chemical processes has increased steadily
over the past 10 years; all atmospheric models now contain at least some of the gas-surface
interactions identified in laboratory studies. However, relatively few global atmospheric
models represent aerosol microphysics in a way that allows for simulation of the impacts of
aircraft aerosols on atmospheric particle densities and surface areas. As a consequence,
there has not yet been much effort directed at modeling the effects of aircraft particle
emissions on atmospheric ozone. We evaluate one such study in Section 2.2.1.3.
2.2.1.1. Effects of Aircraft NO x Emisions on Tropospheric Ozone
Model studies of the impact of NO x emissions from aviation on ozone levels in the UT and
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