Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
in the Southern Hemisphere than the GSFC model but smaller Northern
Hemisphere perturbations. Aircraft-induced NOy enhancements in the middle
stratosphere are greatest in the THINAIR, GSFC, and SLIMCAT models for
Northern Hemisphere and tropical regions. Overall, the AER, CSIRO, LLNL, and
THINAIR models show the greatest Northern Hemisphere isolation of supersonic
aircraft effluent among the participating assessment models. The UNIVAQ, LARC,
and SCTM1 models derive a maximum Northern Hemisphere LS NOy abundance
increase similar to CSIRO. However, these models derive relatively small horizontal
gradients in the LS horizontal spread in NOy and H 2 O, extending from Northern
Hemisphere mid-latitudes to Southern Hemisphere high latitudes, suggesting a
weak tropical/mid-latitude barrier to mixing. The UNIVAQ, SLIMCAT, SCTM1, and
LARC models generate Southern Hemisphere LS NOy and H 2 O magnitudes that
are similar to those of the GSFC model. To first order, the spread in model-derived
changes in total O 3 for the ensemble of scenarios shown in Tables 4-11 and 4-12 is
a direct result of large differences between supersonic aircraft-induced
perturbations in the NOy and H 2 O fields.
4.3.3.2. Profile and Column Ozone Change
The percentage change in profile O 3 for June is shown in Figure 4-6c for scenario
S1c-D. Above 25 km, in all models, local O 3 abundance is reduced as a result of
including supersonic aircraft emissions of NO x and H 2 O. This result is not surprising
because all assessment models represent the NOx (middle stratosphere) and HOx (upper stratosphere) chemical families as prime contributors to odd-oxygen loss
above 25 km, in approximately the same relative importance. Therefore, sensitivity
to NOx and H2O emissions from supersonic aircraft exhaust is similar in these
regions and roughly proportional to calculated perturbations in NOy and H 2 O.
Below 25 km, the relative odd-oxygen loss partitioning between NO x , HO x , and
ClO x -BrO x chemical families is highly model-dependent. This situation is evident in
the calculated local O 3 change. Models that are more HO x dominant in the LS tend
to show a more positive response to added aircraft NO x . The opposite is true for
models that are more NO x dominant. These variations are a result of different
methodologies of transport and chemistry incorporated in the individual models.
The percentage change in total column O3 is shown in Figure 4-6d for scenario S1c-
D. Six of the models (AER, CSIRO, GSFC, LLNL, SCTM1, and UNIVAQ) indicate
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