Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
increases
range from 4
to 7 Tg in
1992, 9 to 17
Tg in 2015,
and 19 to 24
Tg in 2050.
For each
CTM, the
global O3 increase
scales almost
linearly with
aircraft NOx emissionseven
for the
2050 highdemand
sensitivity
study G (3.46
Tg N yr-1 ).
However, O3 production is
less efficient
at high NOx Figure 4-3: Increase in annual average global O3 abundance (Tg
O3) up to 16 km from present and future aircraft emissions.
emissions.
The nearly linear response of global O3 increase to aircraft NOx emissions was not anticipated, given the well-known nonlinear O3 production as a function of NOx (discussed in Chapter 2). The main explanation seems to be that aircraft NOx and associated reservoir species (e.g., HNO3 ) are transported out of aircraft corridors,
where net O 3 production depends more linearly on NO x . We should recognize, however, that all of the global models used in this study have a coarse resolution that
may systematically overestimate the O 3 production. Secondary effects are background increases in CH 4 and CO (as a result of enhanced surface emissions in 2015
and 2050), leading to somewhat more efficient O 3 production per NO x molecule emitted, and the shift of emissions from Northern Hemisphere mid-latitudes toward the
tropics, where background NO x concentrations are smaller.
To further test linearity in O 3 increases to NO x emission beyond the upper limit selected in these model studies, an extremely high NO x emission of 1.5 times the high-
demand, low-technology case (Scenario G) was run with the UiO model. This scenario showed only slight nonlinearity at lower NO x emissions. This extreme simulation
indicated that a level of nonlinearity was reached at northern latitudes where O 3 increases of only 10% were obtained, whereas at southern latitudes, where emissions
are smaller, O 3 increases (approximately 50%) were nearly linear with increases in NO x emissions.
http://www.ipcc.ch/ipccreports/sres/aviation/048.htm (4 von 10)08.05.2008 02:42:21