Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
Aviation and the Global Atmosphere
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4.5. Selection of Model Runs for UV (Chapter 5) and Climate Impact (Chapter 6) Scenario Studies
Other reports in this collection
In this section, the model results that are used as a guide for the ultraviolet B (UV-B) impact (Chapter 5) and the estimation of climate impact (Chapter 6) are selected
and uncertainties are assigned in light of the discussion in Section 4.4. A key uncertainty in assessing the impact of subsonic and supersonic exhaust emissions is that
all models used to assess the aircraft impact are either tropospheric models with limited representation of stratospheric chemistry and transport (tropospheric 3-D
CTMs), or stratospheric 2-D and 3-D CTMs with limited representation of tropospheric processes. In addition, neither the 2-D nor the 3-D models have been designed
to deal specifically with transport processes in the tropopause region, where most aircraft emissions take place.
4.5.1. Model Simulations of Subsonic Aircraft
How well can we calculate the impact from subsonic aircraft in the tropopause region using the tropospheric 3-D CTMs or the stratospheric 2-D models? For these
aircraft, part of the perturbation occurs in the LS and part in the UT.
As discussed in Chapter 2, based on the limited set of observational data that could be chosen for model validation, none of the 3-D CTMs could be picked as the best
assessment model for impact studies of future aircraft emissions. The UiO 3-D model was selected as a representative model for the UV (Chapter 5) and climate
impact studies (Chapter 6), because it gave results in the middle range of model results and it was easily available for sensitivity studies. Height profiles for 30-60°N
zonal mean O3 perturbations for 1992 subsonic emissions (Scenario B-A in Table 4-4) obtained with the AER 2-D model and the UiO 3-D model are shown in Figure 4-
10a. There is reasonable agreement between the two models in the 8-12 km region, near the tropopause. The UiO 3-D model, whose chemistry is most suited to the
troposphere, shows a smaller O3 perturbation in the middle and lowest troposphere. The AER 2-D model, whose chemistry is most suited to the stratosphere, shows a
larger O3 perturbation in the LS. An uncertainty range of a factor of 2 was adopted for O3 perturbation from future subsonic aircraft emissions. This uncertainty range
was based on the range of model results obtained by participating models in basic perturbation studies and results from the limited number of sensitivity studies. A
"fair" confidence is associated with this uncertainty range for 2015, and a "poor" confidence is associated with this uncertainty range for 2050.
Figure 4-10b shows zonal mean O 3 changes for five calculations from the UiO 3-D model. As illustrated in the figure, predicted changes in O 3 from subsonic aircraft
are comparable to changes from surface sources in 2015 and 2050.
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