Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
a) Models are denoted as follows: 2-D-Atmospheric and Environmental Research (AER)
(Weisenstein et al., 1998), Goddard Space Flight Center (GSFC-2D) (Jackman et al.,
1996), Lawrence Livermore National Laboratory (LLNL) (Kinnison et al., 1994), University
of L'Aquila (UNIVAQ-2D) (Pitari et al., 1993); 3-D-German Aerospace Center (DLR)
(ECHAm 3 ) (Sausen and Köhler, 1994), Goddard Space Flight Center (GSFC-3D) (Weaver
et al., 1996), Royal Netherlands Meteorological Institute (KNMI) (Tm 3 ) (Wauben et al.,
1997), University of California at Irvine (UCI/GISS) (Hannegan et al., 1998), University of
Oslo (UiO) (Berntsen and Isaksen, 1997), University of Michigan(UMICH) (Penner et al.,
1991), UNIVAQ-3D (Pitari, 1993).
b) Column amounts calculated between 0-60 km for all models except ECHAm 3 and Tm 3
(0-32 km) and UiO (0-26 km).
c These values are calculated from model results with assumptions of EI(soot) of 0.04 g/kg
fuel, EI(sulfur)
of 0.4 g/kg fuel, and 100% conversion of sulfur to H 2 SO 4 .
Long-term changes in aerosol parameters measured in situ are also small. In situ measurements are important because the number of particles in the upper
troposphere and lowermost stratosphere is dominated by sizes that are too small (< 0.15-mm radius) to be remotely detected. Long-term changes in CN are small in
the 10- to 12-km region of the mid-latitude troposphere, where most of the current aircraft fleet operates (Hofmann, 1993). The 5% yr -1 increase in larger particle
(radius > 0.15 mm) abundances found in lower stratospheric balloon measurements made between 1979 and 1990 was considered consistent with the accumulation of
aircraft sulfur emissions (Hofmann, 1990, 1991). However, the absence of a change in observed stratospheric CN number suggests that the trend in the larger
particles is the result of the growth of existing particles rather than nucleation of new particles. Model results show that the contribution of the current subsonic fleet to
aerosol mass amounts between 15 and 20 km is about 100 times smaller than the observed aerosol amounts (Section 3.3.4; Bekki and Pyle, 1992). Previous balloonborne
CN counters did not measure particles below 10 nm in radius, which are now detected with more modern CN counters and dominate aerosol number in aircraft
plumes. Moreover, the attribution of aerosol changes to aircraft is complicated by changes in surface sources of sulfur and episodic strong injections of sulfur from
volcanic eruptions (Hitchman et al., 1994; Barnes and Hofmann, 1997; Thomason et al., 1997a,b). Hence, the contribution of aircraft emissions to changes or possible
trends in these regions is difficult to determine at present.
3.3.4. Modeling Sulfate Aerosol Perturbations Caused by Aircraft
3.3.4.1. Subsonic Aircraft
Global models are required to evaluate the atmospheric impact of aerosol generated by subsonic aircraft (Friedl, 1997; Brasseur et al., 1998). The global distribution of
tropospheric sulfur species has been investigated using various three-dimensional (3-D) models (Langner and Rodhe, 1991; Penner et al., 1994; Chin et al., 1996;
Feichter et al., 1996; Pham et al., 1996; Schwartz, 1996). Because most models have been developed to investigate regional or global effects of surface emissions in
the lower or middle troposphere, few have addressed the potential impact of aviation sources on aerosol parameters in the upper troposphere and lower stratosphere.
A systematic model study has been carried out with a suite of two-dimensional (2-D) and 3-D atmospheric models to determine upper bounds for the accumulation of
aviation aerosol in the atmosphere (Danilin et al., 1998). Each model computed the steady-state global distribution of a passive tracer emitted into the model
atmosphere with the same rate and distribution as aviation fuel use, based on the NASA 1992 database (see Chapter 9). The only sink for the passive tracer is below
400 hPa (approximately 7 km), where it is removed with a 1/e-folding time of 5 days. The resultant global tracer distribution can be used to provide estimates of steady-
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