Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
Aviation and the Global Atmosphere
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5.4.2. Results
5.4.2.1. Ozone Column Changes
Figure 5-5 shows calculated ozone column changes as a function of latitude for July and October and
for a range of scenarios. The top panel shows the change in columns attributable to subsonic fleets
over the period 1992-2050 relative to a background atmosphere of the same year. The corresponding
calculations for 1970 are not shown, but the effects attributable to aircraft for this period were very
much smaller than any shown in the top panel of Figure 5-5 (see Figures 5-6, 5-7, and 5-8). The
middle panel shows a corresponding calculation for the hybrid (subsonic+supersonic) fleets for 2015
and 2050, and the bottom panel shows the changes in background between 2050 and 1970, between
2015 and 1970, and between 1992 and 1970. The major features of the aircraft impact on ozone
have been discussed in Chapter 4. For the background atmospheres (bottom panel), the calculations
predict a systematic increase in ozone after 1992. For the Southern Hemisphere, this outcome is
largely because of the expected decrease in bromine and chlorine. The additional increase in ozone
in the Northern Hemisphere relative to the Southern Hemisphere is because the projected release of
NO x at the surface is greater in the Northern Hemisphere.
5.4.2.2. Calculated Changes in Ozone Compared to Changes in UV
An alternative to the method of presentation of results used in Figure 5-5 is to show the evolution of
changes in ozone and UV as a function of time, as in Figure 5-6. Here, calculated ozone and UVery
averaged between 65°S and 65°N for July and for a range of scenarios are referred to calculated
background values for 1970. When averages are taken over a broad latitude band such as that in
Figure 5-6, seasonal behavior is removed, to a large extent. However, a particular latitude may exhibit
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