Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
Trends in UT ozone for the time period encompassing large growth in aircraft fuel
consumption (1970 to the present) are available from a number of ozonesonde stations. All
of the sonde stations at middle and high latitudes of the Northern Hemisphere show a
stratospheric decrease at altitudes between the tropopause and ~24 km for the period 1970-
96. Upper tropospheric trends vary substantially among stations, with increases of 10-20%/
decade over Europe, decreases of 5-10%/decade over Canada and the eastern United
States, and no trend over Japan (WMO-UNEP, 1999). Neither aircraft nor surface NOx emissions-both showing little geographical variation in their European, North American, and
Asian trends (Logan, 1994)-are consistent with observed ozone trend variations.
Detailed time-series analysis of ozone trend data in an area of heavy aircraft traffic (i.e.,
west-central Europe) reveals that air traffic growth is unlikely to be a primary factor in the
observed upper tropospheric trend. For example, the sonde observations at
Hohenpeissenberg, Germany, clearly show a mean increase in ozone of ~10%/decade
below ~9-km altitude between 1970-96 (Figure 2-5). However, most of the increase
occurred before 1985 (WMO-UNEP, 1999), even though air traffic growth remained steady,
and the ozone trend for the period 1980-96 is slightly negative in the UT. The lack of growth
in ozone after 1985 mimics the lack of growth of surface emissions of NO x (Logan, 1994).
Decreases in the amount of ozone transported to the UT from the LS, because of reductions
in stratospheric ozone abundance and/or weakening of dynamical transport, may also be a
factor in the observed trend during the 1980s and 1990s.
In situ aircraft sampling of ozone in the 9-13 km region that has occurred sporadically over
the past 20 years provides complementary data sets for use in understanding ozone
climatology in the tropopause region. In 1994, a focused effort to collect climatological
ozone data from aircraft platforms was initiated as the MOZAIC program (Marenco et al.,
1999; Thouret et al., 1999). This database is now sufficiently long to address a number of
important issues related to tropopause heights and seasonal variations, although it cannot
yet address the issue of long-term trends.
2.2.2.2. Other Diagnostics of Large-Scale Aviation Impacts
Figure 2-6: (a) Median NOx mixing ratios measured between 9 and
12 km during a number of in situ aircraft campaigns (compiled in
Emmons et al., 1997); (b) NOx concentration field in the altitude
regions between 300 and 190 hPa obtained by the measurements of
NOxAR.
As discussed in previous sections, ambient levels of NO x and soot are likely to be affected by aircraft to a greater extent than ozone. Accordingly, a comprehensive set
of NO x and aerosol measurements taken over a wide range of locations and over the period of the past 20 years could provide a basis for evaluating aircraft impacts
on these ozone-related species. Compared to the historical record for ozone, however, the available information on NO x and aerosol is sparser and was obtained only
by in situ sampling from aircraft and balloons (Hofmann, 1993; Blake and Kato, 1995; Emmons et al., 1997). Satellite data are available for lower stratospheric aerosol,
but the data record is relatively short and heavily influenced by recent volcanic eruptions. Analysis of NO x and aerosol trends would be exceedingly difficult to interpret
because the aircraft source would be convolved with many other increasing sources of anthropogenic NO x and aerosol. In addition, the high degree of air mass
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