Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
a) Detectable only by ultrafine particle counters (particles smaller than 2-3 nm radius are not detected). Calculations by Yu and Turco (1997) for
average FSC consistent with observed data.
b) Properties highly variable; size distributions often bimodal. Ranges include small (> 10 nm) particles. Large particle mode (~100 nm) often similar
to stratospheric aerosol particles (Hofmann, 1993; Yue et al., 1994; Schröder and Ström, 1997; Solomon et al., 1997; Hofmann et al., 1998). High
range of values inferred from satellite extinction data and represents mixtures of aerosols and subvisible clouds.
c), d) Yue et al., 1994; Kent et al., 1995; Borrmann et al., 1997; Thomason et al., 1997b.
e) Hagen et al., 1992; Rickey, 1995; Petzold et al., 1999.
f) Only largest soot particles with longest atmospheric lifetimes are measured by wire impactors (Sheridan et al., 1994; Blake and Kato, 1995;
Pueschel et al., 1997). Uncertainties in total surface area introduced by fractal geometry of particles.
g) Kärcher et al., 1996b, 1998a; Petzold et al., 1997.
h) Values representative of contrail core for low ice-supersaturation (Heymsfield et al., 1998a; Schröder et al., 1998b) (see also Sections 3.4.4 and
3.6.3). Far larger particles are observed for large ice-supersaturation (Knollenberg, 1972; Gayet et al., 1996).
i) Ström et al., 1997; Schröder et al., 1998b. Larger values are observed in warm cirrus clouds (Heymsfield, 1993; see also Sections 3.4.4 and
3.6.3).
j) Results of fuel tracer simulations discussed in Section 3.3.4. Values shown represent upper bounds to zonal mean perturbations caused by
emissions of the 1992 aircraft fleet. Results are representative of flight levels at northern mid-latitudes and are calculated using the range of values
of computed tracer concentrations from all models and assuming a fuel sulfur content of 0.4 g/kg fuel, a 5% conversion of sulfur to sulfate aerosol,
an EI(soot) of 0.04 g/kg fuel, and a mean particle size of 10(20) nm for sulfate (soot) particles.
Once formed, the new volatile particles interact with nonvolatile and contrail ice particles through the processes of coagulation, freezing, condensation, and
evaporation (Figure 3-1). Calculations show that the new liquid particles grow and shrink as a function of relative humidity, whereas H 2 SO 4 molecules that enter the
droplets stay in the liquid phase because of their very low saturation vapor pressure (Mirabel and Katz, 1974). They also suggest that volatile particles may take up
HNO 3 and H 2 O in the near field (Kärcher, 1996) to form particles with compositions similar to those found in cold regions of the stratosphere. These particles may
persist in cold (< 200 K), HNO 3 -rich stratospheric air but will be short-lived (< 1 min) otherwise. As the plume continues to dilute with ambient air, abundant newly
formed volatile particles remain at nanometer sizes and therefore add substantially to the overall aerosol surface area and abundance (Danilin et al., 1997). Their
efficiency for heterogeneous chemistry and cloud formation, however, is size- and composition-dependent (Kärcher, 1997). They may be too small to act as efficient
cloud- or ice-forming nuclei in the background atmosphere unless the air mass containing the aerosol is lifted or cooled or the relative humidity increases. Although
studies exist on heterogeneous plume processing along selected trajectories (Danilin et al., 1994), systematic investigations of heterogeneous chemistry coupled to
plume aerosol dynamics remain to be performed (Chapter 2).
The evolution of volatile particles is significantly altered if a contrail forms. In contrails,
volatile particles have to grow to sizes greater than about 100 nm via uptake of ambient
H 2 O before most of them freeze (Section 3.2.4.2). As ice particles grow in size by
deposition of H 2 O, they may also scavenge other volatile and soot particles (Anderson et
al., 1998a,b; Schröder et al., 1998a). Thus, contrails are expected to contain fewer small
particles than non-contrail plumes because of enhanced scavenging losses. After
evaporation of contrail ice crystals, the residual volatile and soot cores remain as particles in
the atmosphere (Figure 3-1). This contrail processing is expected to modify the particle size
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