Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
smaller depletions in the tropics and larger depletions at mid- and high latitudes.
The other three models (LARC, SLIMCAT, and THINAIR) show more complicated
features. The LARC model predicts increases in Northern Hemisphere mid- and
high latitudes and decreases in the tropics. The SLIMCAT model predicts
decreases of more than 0.6% in the tropics, with less depletion predicted at
Northern Hemisphere mid- and high latitudes and Southern Hemisphere mid-
Figure 4-7: Northern Hemisphere total O3 column change as a function of EI
(NOx) in 2015 for an HSCT fleet size of 500 active aircraft with (a) SA0 sulfate
distribution and (b) 4xSA0 sulfate distribution with no sulfur aircraft emissions.
latitudes. The THINAIR model generally predicts larger depletions at lower latitudes. Decreases in Northern Hemisphere polar latitudes of greater than 1% are shown
in the AER model results. The GSFC and SLIMCAT models predict decreases in the Southern Hemisphere polar spring of greater than 1%.
4.3.3.3. Column Ozone Sensitivity to Supersonic Emission of NO x and H 2O
Sensitivity studies of supersonic engine emissions of H 2 O and NO x were carried out. These
studies investigated individual and combined impacts on O 3 from H 2 O and NO x emissions
within an atmosphere that was volcanically clean (SA0). In Figure 4-7a, the change in
annual average Northern Hemisphere total column O 3 as a function of EI(NO x ) is shown for
a fleet of 500 supersonic aircraft in the year 2015 (Scenarios S1b-e). The reference
atmosphere included emissions from a representative 2015 fleet of subsonic aircraft. Under
the conditions of these scenarios, the models predict that water emissions [corresponding to
EI(NO x )=0] have the most significant impact. For EI(NO x )=0, the participating models all
derive a total O 3 depletion in the 0.2-0.6% range.
For low emission indices of NO x [EI(NO x )=5 to 10], the predicted decrease in O 3 is
dominated by emitted H 2 O; in most models, the addition of NO x emissions leads to less
predicted O 3 depletion. Because O 3 loss in the lower stratosphere tends to be dominated by
HO x constituents and supersonic aircraft emissions are most important in the lower
stratosphere (see Figure 4-6), the predicted importance of H 2 O emissions is
understandable.
Several models show relatively little sensitivity to NO Figure 4-8: Northern Hemisphere total O3 column change as a
x emissions over the EI(NOx )=5 to 15
function of surface area density (SAD) between 14-21 km and 33-90°
range. Including NOx emission at an EI(NOx )=5 level, S1c had little effect on total column
N. Calculations are for EI(NOx)=5 and an HSCT fleet size of 500
O3 change for the LLNL, GSFC, and CSIRO models [relative to EI (NOx )=0]. For the AER, aircraft in the 2015 atmosphere. The 27, 38, 82, and 111% change in
SAD correspond to SA7, SA5, SA1, and SA3 as listed in Table 4-9,
SLIMCAT, and UNIVAQ models, added NOx buffers the larger total O3 depletion derived
respectively.
when H2O is the only emitted constituent. When NOx emission is included, six of the models
(CSIRO, GSFC, LLNL, SCTM1, SLIMCAT, and THINAIR) calculate a larger O3 depletion as
EI(NOx ) increases from 5 to 15 (S1c-e). The AER model showed little sensitivity to EI(NOx ) in this range. Within the same range, the LARC and UNIVAQ models
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