Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
O 3 -The O 3 increase is restricted to northern mid- and high-latitudes, with maximum increases in the UT and LS. Subsonic aircraft are predicted to cause a maximum
annual average O 3 increase of 7-11 ppbv in 2015 in the latitude band 30-60°N at 10-13 km altitude. This result corresponds to an increase of approximately 5-10%.
The calculated increase in global average O 3 with increasing NO x emission from aircraft is in broad agreement among different models. Although the models show
general linearity for O 3 increase from NO x emission, O 3 production is less efficient at high NO x emission. The global average O 3 increase from aircraft NO x emissions
is not very sensitive to projected changes in atmospheric composition for the model scenarios investigated here.
The O3 increase may be mitigated somewhat by emitted sulfate, leading to production of chlorine moNOxide (ClO), bromine moNOxide (BrO), and hydrogen dioxide
(HO2 ) in the LS. This process, however, has not been included in the model calculations presented in this report.
CH4-As a result of increases in tropospheric hydroxyl (OH) caused by aircraft NOx emissions, CH4 removal rates are computed to increase by 1.6-2.9% in 2015 and
2.3-4.3% in 2050. The possible influence of changes in CH4 on climate are discussed in Chapter 6.
Calculations for Supersonic Aircraft Scenarios
Because the supersonic fleet is still in its design stage, the range of emissions, fleet size, and cruise altitude covered by supersonic scenarios is larger than for
subsonic aircraft. For a nominal cruise altitude of 19 km, the largest impacts of proposed supersonic aircraft occur in the stratosphere.
The predicted decrease of O 3 in the stratosphere is most sensitive to emissions of H 2 O, oxides of sulfur (SO x O), and NO x .
● For low emission indices of NO x [5-10 g nitrogen dioxide (NO 2 ) kg -1 fuel], the predicted decrease in O 3 is dominated by emitted H 2 O.
● The amount of emitted sulfur dioxide (SO2 ) is important in determining the magnitude of the calculated ozone decrease. The response to sulfur depends on how
much SO2 is converted to sulfate particles in the aircraft exhaust plume, with larger depletions accompanying larger conversions.
● The calculated change in O3 also depends on background sulfate surface area density (SAD), which is variable because of volcanic input. The computed change in
O3 is not very sensitive to projected changes in chlorine loading and trace gases for an assumed fleet size of 500 aircraft, using a background sulfate SAD condition in
the model simulation.
● Changes in cruise altitude produce different results: Higher (lower) cruise altitudes result in larger (smaller) O3 depletions.
Results reported here correspond to changes in O3 when a supersonic fleet of aircraft replaces a portion of subsonic flights. The baseline computations assume that
supersonic aircraft have a cruise altitude of 19 km, an emission index for water EI(H2O)=1230 (1230 g H2O kg-1 fuel), EI(NOx )=5 (5 g NO2 kg-1 fuel), and a range of
values for EI(SO2 ).
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