Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
concentrations using observations, or they prescribe O 3 fluxes from the stratosphere into
the troposphere. The use of these boundary conditions could lead to a calculated impact
on stratospheric O3 that is too small. It may also be that the ECHAm3 /CHEM model has
too efficient transport in the LS.
The effect of constraining concentrations and fluxes at the upper boundary of the 3-D
models was checked by running the stratospheric 2-D Atmospheric and Environmental
Research, Inc. (AER) model for the same subsonic scenario. Consistent with the 3-D
models, the AER model calculates a maximum O 3 increase of 8-10 ppbv in the Northern
Hemisphere at an altitude of 8-12 km. In the stratosphere at 16 km, small increases of 2
ppbv in the Southern Hemisphere and 6 ppbv in the Northern Hemisphere are
calculated-somewhat higher, but consistent with most 3-D models. Calculated O3 increases are strongest in the UT and the LS. In the lower troposphere (< 6 km), the
increase is reduced by a factor of about 5 in mixing ratio compared to the UT. All models
calculate that about 85% of the O3 increase for 1992 is in the Northern Hemisphere; for
2015 and 2050, the portions are about 80 and 75%, respectively.
Although emissions of precursor NOx are spatially distributed heterogeneously, the
resulting O3 increases are distributed more uniformly as a result of the combined effects
of strong longitudinal mixing and the relatively long residence time of O3 in the free
troposphere and LS. All models show efficient transport of excess O3 from source
regions at mid-latitudes to high latitudes, where the residence time of O3 is particularly
long as a result of decreased deposition (Stevenson et al., 1997; Wauben et al., 1997;
Berntsen and Isaksen, 1999).
There may be a strong seasonal cycle in the calculated impact of aircraft emissions on
O 3 . For example, using the same emission scenarios, the UiO and the UKMO models
calculate a 40% larger increase of O 3 in the Northern Hemisphere in April compared to
July (Stevenson et al., 1997; Berntsen and Isaksen, 1999). Other models find much
weaker seasonal cycles (e.g., IMAGES/BISA and ECHAm3 /CHEM), or find maximum
increases in summer (e.g., Tm3 /KNMI and HARVARD). These seasonal differences are
probably associated with different background NOx conditions in the different models
(see Section 4.2.3.2).
4.2.3.2. NO x Perturbation
http://www.ipcc.ch/ipccreports/sres/aviation/048.htm (2 von 10)08.05.2008 02:42:21
Figure 4-1: Annual (2015) and zonal average increases of ozone volume
mixing ratios [ppbv] from aircraft emissions calculated by six 3-D models.
The IMAGES/BISA model does not give results above 14 km, and the
HARVARD model does not give results above 12 km.