Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
Symbol Description Chapter 4 Reference
1992 bg 1992 background Scenario A: Table 4-4
1992 ss 1992 including subsonics Scenario B: Table 4-4
2015 bg 2015 background Scenario C: Table 4-4
2015 ss 2015 including subsonics Scenario D: Table 4.4
2015 hf 2015 subsonic/supersonic hybrid fleet Scenario S1k: Table 4-11
2050 bg 2050 background Scenario E: Table 4-4
2050 ss 2050 including subsonics Scenario F: Table 4-4
2050 hf 2050 subsonic/supersonic hybrid fleet Scenario S9h: Table 4-12
1970 bg 1970 background Deduced from 1992 bg
1970 ss 1970 subsonic Deduced from 1992 ss
These absolute differences are applied to 1992ss to produce 1992bg, the 1992 background atmosphere, which is free of
inputs from aircraft emissions. A model calculation is then carried out using the prescribed background scenario for
2015. The results of these calculations are compared with the similar calculation for 1992, and the absolute difference
obtained from the model calculations is applied to 1992bg to obtain 2015bg, the 2015 background atmosphere.
Comparison of a model calculation for a 2015 atmosphere that contains inputs attributable to aviation, assuming only
subsonic aircraft will be operating, with the model calculation for the 2015 background atmosphere provides an estimate
of absolute changes in ozone concentration between these two calculations. These differences are applied to 2015bg to
produce 2015ss, the 2015 atmosphere that includes the effects of emissions from a purely subsonic fleet of aircraft.
Clearly, an analogous approach can be adopted to obtain the required information for 2050 and for 1970. Chapter 4 has
provided mixing ratio differences calculated for the impact of aviation on ozone profiles for the latitudes and seasons
shown in Table 5-1. The authors of Chapter 4 chose results from the Oslo 3-D model and the Atmospheric and
Environmental Research, Inc. (AER) 2-D model as representative of the subsonic and supersonic scenario calculations,
respectively. Table 5-2 shows the scenarios considered here, with references to the relevant Chapter 4 tables. The
method adopted in Chapter 4 for expressing the range in uncertainties for the ozone mixing ratio differences is
discussed in Section 5.4.2.3. Figure 5-3 attempts to highlight the fact that, although 1992bg, 2015bg, and 2015ss are
derived from model calculations, they have the measurements of 1992ss as a reference. The implication of this
approach is that, although ozone concentrations derived from models clearly have uncertainties, the differences
obtained between any two model calculations may be more accurate than the absolute concentrations in either model
calculation. This assumption is questionable and must be regarded more as an assumption that allows UV calculations
to proceed than one that can be defended strongly. The approach does have the advantage that UV calculations derived
from 1992bg, 2015bg, and 2015ss are not based entirely on model calculations. It should be noted that, in assigning
differences between model calculations to measured values in 1992ss, absolute differences in model calculations have
been chosen rather than percentage differences. Again, the approach taken cannot be defended rigorously.
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