Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
4.5.2. Model Simulations of Supersonic Aircraft
The basic assumption in market studies that determine the routing and size of the supersonic fleet is that the supersonic fleet will replace certain routes of the given
subsonic fleet, corresponding to about 10% of the subsonic fuel burn. The results of these studies were used to generate the fuel burn for a combined fleet consisting
of a supersonic fleet with a modified subsonic fleet. For this reason, it is more appropriate to compare the effect of the combined fleet to the subsonic fleet, rather than
to look at the supersonic fleet in isolation. Taking 2015 as an example, numerical results were generated for the 2015 atmosphere without aircraft (scenario C), the
2015 atmosphere with the standard subsonic fleet (scenario D), and the 2015 atmosphere with the combined fleet (scenario S1k). Recognizing the uncertainties
concerning the tropospheric response generated by the stratospheric models, the strategy is to use the change in O 3 computed between S1k and D and the results
from the tropospheric models from scenario D minus scenario C for the effect of the subsonic fleet, after adjusting for the 10% difference in fuel burn.
For supersonic aircraft influences on UV effects (Chapter 5) and radiative forcing and climate change (Chapter 6), we have chosen a central or most probable emission
scenario (S1k-2015 and S9h-2050), along with a representative assessment model (AER). This emission scenario assumes a SO2 gas-to-particle conversion of 10%.
The AER model was selected because it was the model that calculated and supplied the enhanced gas-to-particle sulfate aerosol SAD that was used in all participating
assessment models. The middle plot in Figure 4-11 shows the percentage change in column O3 for the AER model using the S1k scenario. At all latitudes and months,
the AER model derives a reduction in total column O 3 .
Because of coupling between chemistry and transport, there is no simple way to scale O 3 change profiles based on a priori estimates of uncertainties. It is possible to
get an idea of the uncertainties by looking at the assembly of results from various scenarios performed by different models. Concentrating on the first group of
scenarios in Table 4-11 (which represent a 500-plane Mach 2.4 fleet with EI(NOx)=5 flying in a clean sulfate background), we picked S1c from UNIVAQ and S1h from
GSFC as representative of the range of possible results. The differences in computed O 3 changes by the AER, UNIVAQ, and GSFC models in northern mid-latitudes
are illustrated in Figure 4-12a for 2015. The UNIVAQ and GSFC models were picked because these models represent different ways of treating transport and PSCs
that consistently produce the smallest and largest O 3 depletion in most scenarios. The sampling of scenarios also covers the possible range of effects from different
assumptions of gas-to-particle conversion in plume processing of SO 2 emission. For 2050, we focus on a 1,000-plane Mach 2.4 fleet with EI(NOx)=5. The AER S9h
scenario is taken as the central case, and the lower and upper extremes were taken to be S9d for UNIVAQ and S9f for GSFC. The differences in O 3 changes
computed by the AER, UNIVAQ, and GSFC models in northern mid-latitudes are illustrated in Figure 4-12b for 2050.
It is also important to note which uncertainties, among those discussed in Chapters 2 and 3, are not included in this range. All of the models used rate data from
DeMore et al. (1997). A previous study (described in Stolarski et al., 1995) showed that uncertainties in rate data could lead to an uncertainty in NH O 3 column change
of ±1%. Current studies indicate that most models underestimate the mean age of air as defined by inert tracers that enter the stratosphere via the tropical tropopause.
Given that there appears to be a positive correlation between calculated increases in NOy and H 2 O from HSCT and calculated mean age, it has been suggested that
models that underestimate age will also underestimate NOy and H 2 O increases from HSCT. It is difficult to quantify the uncertainty given current information. We did
not consider the effect of plume processing and possible changes (in temperature and transport circulation) in the future background atmosphere. Finally, the range
cited does not include different technology options for different EI(NOx), different cruise altitudes, and different fleet sizes.
It is possible to arrive at a subjective estimate for uncertainty estimates for changes in column O3 . This value can be used to calculate changes in UV because that
depends mostly on the changes in column in the lower stratosphere. It is less obvious whether this value can be used to estimate uncertainties in radiative forcing.
http://www.ipcc.ch/ipccreports/sres/aviation/052.htm (2 von 3)08.05.2008 02:42:32