Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
Figure 4-9 (S1c, S2a, and S2b) shows the effect of lowering or raising the supersonic cruise altitude by 2 km relative to the baseline flight cruise altitude band of 17-20
km for an assumed fleet of 500 EI(NOx )=5 aircraft. In most altitude sensitivity studies, ambient SAD was considered to be volcanically clean, and sulfur emission by
HSCT aircraft was not included. The model-derived change in annual average Northern Hemisphere total column O3 had a large dependence on emission altitude in
participating assessment models. This cruise altitude impact on O3 highlights the fact that as NOx is emitted lower in the stratosphere, the residence time of supersonic
aircraft emitted NOx is significantly shorter. In addition, at a lower cruise altitude the chemical regime is quite different, and past modeling studies have shown that a
crossover point exists where an additional NOx molecule will produce O3 based on the well-known CH4-smog mechanism (Johnston and Quitevis, 1975). When the
cruise altitude is shifted higher, emissions have a longer stratospheric lifetime and can be transported more readily to regions dominated by NOx destruction of O3 .
Each of these models showed less total column O3 depletion when the cruise altitude was shifted down by 2 km. Three models also investigated sensitivity to higher
values of EI(NOx ) (10 and 15) at the lower cruise altitude (S2c-d). The model-derived total column O3 change generally increased in the direction of higher EI(NOx ).
These results are consistent with the 1995 NASA supersonic assessment (Stolarski et al., 1995).
Two models (AER and UNIVAQ) did look at sensitivity to cruise altitude with increased SAD from sulfur emissions as 50% particles (S7c). In this scenario, an
enhanced SAD was not supplied but derived within the 2-D model, coupled with a sulfate microphysical model. The model-derived annual average Northern
Hemisphere depletion in total column O 3 was reduced from -1.0 (S7a) to -0.6% (S7c) in the AER model and from -0.5 (S7a) to -0.2% (S7c) in the UNIVAQ model when
the supersonic cruise altitude was lowered by 2 km. The opposite impact was derived by the AER model when the cruise altitude was raised 2 km. Here, the modelderived
annual average Northern Hemisphere depletion in total O 3 increased from -1.0 (S7a) to -1.4 % (S7b) in the AER model and from -0.5 to -0.7% in the UNIVAQ
model.
4.3.3.7.2. Supersonic fleet size sensitivity
In this assessment, fleet sizes of 500 and 1,000 supersonic aircraft were considered at EI(NO x ) values of 5 and 10. The increase in fleet size from 500 to 1,000 aircraft
included additional routes as well as additional aircraft; as a consequence, the geographical distribution of emissions changes with proportionally more flights in the
tropics (Baughcum and Henderson, 1998). In addition, by increasing the fleet size, the amount of H 2 O emitted is also increased proportionally. For most of the cases
considered, doubling the fleet size had a nearly linear effect on the Northern Hemisphere column O 3 reduction. The exception is the UNIVAQ model, which showed
almost no change with increasing fleet size. For the 2050 atmosphere with aircraft sulfur emission as 50% particles, increasing the fleet size from 500 to 1,000 aircraft
has a less than linear effect, especially with the AER model.
http://www.ipcc.ch/ipccreports/sres/aviation/050.htm (9 von 10)08.05.2008 02:42:29
Table 4-14a: Mid-latitude lower stratospheric mass density(MD, ng/cm 3 ) and SAD (µm 2 /cm 3 ) with/without subsonic
aircraft in 2015 [annual average, EI(SO 2 )=0.4 g/kg, 10-14 km, 30-60°N).