Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
significant seasonal behavior in the calculated departure from background values for 1970. For
example, Figure 5-7 shows calculated changes for 45°N for January, and Figure 5-8 shows the
corresponding calculations for July. Comparison of Figures 5-7 and 5-8 shows that, although the
calculated ozone and UVery for the background in 2050 for January are little different from the
corresponding values for 1970, there are significant departures in July. This result is almost certainly
because of the increased ozone calculated for the upper troposphere in 2050 resulting from the
increase in NO x released from the surface of the Earth relative to 1970.
The method of presentation shown in Figures 5-6, 5-7, and 5-8 has the advantage that the predicted
impact of either the hybrid fleet or the subsonic fleet on the background atmosphere at the
corresponding time can easily be determined from the diagram; in addition, the departure for any of
the scenarios from the calculated value for the background atmosphere in 1970 is readily determined.
However, this method of presentation does not show changes as a function of latitude; that
information is provided in Figure 5-9, which shows percentage UVery changes for July and October
corresponding to ozone changes in Figure 5-5. The labels on the diagram refer to the atmospheres
defined in Table 5-2.
The three panels in Figure 5-9 show the calculated changes in UVery for subsonics (top), subsonics
+supersonics (middle), and changes in ground emissions (bottom). Several trends are clear from
Figure 5-9. First, the impact of subsonic aviation is significantly greater in 2015 and 2050 than in 1992
(top panel); at northern mid-latitudes, the impact of the subsonic fleet is roughly proportional to the
levels of aircraft emissions assumed. Second, when the effect of the hybrid fleet is compared to the
corresponding background, there is an increase in UVery relative to the case where a pure subsonic
fleet is considered (compare the top and middle panels). Third, calculated changes in UVery relative
to 1970 for present and future background atmospheres show an increase in 1992 and a systematic
decrease thereafter (bottom panel). This behavior is directly related to the levels of bromine and
chlorine assumed for the stratosphere and the amount of NO x assumed to be released from the
surface of the Earth.
5.4.2.3. Treatment of Uncertainties in Ozone Change and UVery Change Calculations
The calculations reported in Sections 5.4.2.1 and 5.4.2.2 are based on information provided in
Chapter 4. In that chapter, calculations were carried out for a number of scenarios corresponding to
the years 1992, 2015, and 2050. For 1992, the calculated impact of the subsonic fleet on atmospheric
ozone was estimated using a 3-D CTM. Similar calculations were performed to assess the expected
impact of subsonic aircraft in 2015 and 2050. In addition, the impact of hybrid fleets of subsonic and
supersonic aircraft for 2015 and 2050 were obtained using a combination of 2-D and 3-D chemical
transport calculations. The results for the hybrid fleet in Sections 5.4.2.1 and 5.4.2.2 are based on
calculations provided in Chapter 4 for the AER model for scenarios S1k-D for 2015 and S9h-D9 for
2050. These scenarios are defined in Tables 4-10, 4-11, and 4-12. In addition to performing these
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Figure 5-6: Calculated ozone and UVery averaged between
65°S and 65°N for July and referred to the calculated
background values for 1970.