Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
Aviation and the Global Atmosphere
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EXECUTIVE SUMMARY
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Aircraft emit a number of chemically active species that can alter the concentration of atmospheric ozone. The species with the greatest potential impact are nitric
oxide (NO) and nitrogen dioxide (NO 2 ) (collectively termed NO x ), sulfur oxides, water, and soot.
Ozone concentrations in the upper troposphere and lowermost stratosphere are expected to increase in response to NO x increases and decrease in response to sulfur
and water increases. At higher altitudes, increases in NO x lead to decreases in ozone.
Soot surfaces destroy ozone and possibly convert nitric acid to NO x . However, because atmospheric soot reactions are highly unlikely to be catalytic and because
ambient soot concentrations are low, the effect on ambient ozone is expected to be negligible.
Soot surfaces destroy ozone and possibly convert nitric acid to NOx . However, because atmospheric soot reactions are highly unlikely to be catalytic and because
ambient soot concentrations are low, the effect on ambient ozone is expected to be negligible.
Aircraft emissions are calculated to have increased NOx at cruise altitudes in northern mid-latitudes by approximately 20%. The uncertainty in this calculation is
primarily related to uncertainties in the NOx chemical lifetime and in the relative magnitude of the aircraft source compared to lightning, rapid vertical convection of
surface NOx , and other sources of upper tropospheric NOx . The calculated increase is substantially smaller than the observed variability in NOx .
NOx emissions from current aircraft are calculated to have increased ozone by about 6% in the region 30-60°N latitude and 9-13 km altitude. Calculated total ozone
column changes in this latitude range are approximately 0.4%. Calculated effects are substantially smaller outside this region. Some of the uncertainty in these
calculations is captured by the range of model results. However, the models are notably deficient in coupling representations of stratospheric and tropospheric
chemistry and in describing exhaust plume processes, HOx sources, and non-methane chemistry in the upper troposphere. In addition, there is high uncertainty
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