Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
LS have been performed with increasing sophistication since the 1970s. Most studies set up
a base case without aircraft NO x emissions and a perturbed case with the aircraft source
added. Differences in atmospheric composition and, ultimately, radiative forcing between
the two cases are attributed to the influence of aircraft emissions. There are detailed
differences among the many model studies that arise because of differences in the aircraft
emission inventories employed. There are, however, many other more crucial differences in
the model studies: The extent and accuracy of the treatment of atmospheric chemistry
processes; the treatment of other NO x sources besides aircraft; the treatment of dispersion,
transport, and advection of NO x species; and the adequacy of the treatment of the
underpinning description of the coupled chemistry and the global atmospheric circulation in
the UT and LS.
Many of the model studies note that the bulk of aircraft NOx emissions from subsonic
aviation occurs in an atmospheric region that is sensitive to these emissions. Because of Figure 2-3: Maximum percentage increase in ozone concentrations,
low background NOx levels-typically 50-200 ppt-in the mid-latitude UT and LS, high NO/NO2 in principal traffic areas, in the 9- to 13-km altitude range, 30-60°N
latitude range, during summer, normalized by assumed global aircraft
ratios, and low HOx concentrations, ozone production (in terms of ozone molecules) per
NOx emission to 0.5 Tg N yr-1 and plotted against the year the
NOx molecule is more efficient here than anywhere else in the atmosphere. Because the calculation was performed.
greenhouse blanketing produced by a given atmospheric ozone increment is directly
proportional to the temperature contrast between radiation absorbed and radiation emitted,
radiative forcing efficiency is greatest for ozone changes near the tropopause (Lacis et al., 1990), though its climate sensitivity may have a different response (Hansen
et al., 1997).
http://www.ipcc.ch/ipccreports/sres/aviation/026.htm (2 von 6)08.05.2008 02:41:43
Table 2-1: Calculated changes in ozone inprincipal traffic areas and 9- to 13-km region during summer for five
selected models employed in Chapter 4 for the 1992 aircraft subsonic fleet NOx emissions of 0.5 Tg N yr-1 (see
Chapter 9), together with the range of previous studies shown in Figure 2-3.