Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
Aviation and the Global Atmosphere
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3.3. Regional and Global-Scale Impact of Aviation on Aerosols
3.3.1. Global Aircraft Emissions and Aerosol Sources
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Aircraft emissions may cause changes in the background distribution of soot and sulfuric acid aerosols at regional and global scales. In this section, observations and
model results are used to evaluate these potential aircraft-induced changes.
Soot and sulfur mass emissions from aircraft are small compared with other global emissions from anthropogenic and natural sources (Table 3-2). However, aircraft
emissions occur in the upper troposphere and lower stratosphere, where background values are lower and removal processes are much less effective than near the
Earth's surface. Moreover, aircraft aerosol particles tend to be smaller than background particles, so small emission masses may still cause large changes in aerosol
number and surface area densities. In addition, aerosol particles from aircraft can participate in the formation of contrails and clouds in the upper troposphere, hence
potentially alter the radiative balance of the atmosphere (Section 3.6).
About 93% of all aviation fuel is consumed in the Northern Hemisphere and 7% in the
Southern Hemisphere (Baughcum et al., 1996; see Chapter 9). Within the Northern
Hemisphere, 76% of aviation fuel is consumed at mid- and polar latitudes (> 30°N). The
geographical and altitude distribution of current aviation fuel consumption implies that the
largest changes in aerosol and gas composition from aviation will be at northern midlatitudes
at altitudes of 10 to 12 km.
3.3.2. Sulfate Aerosol
3.3.2.1. Stratosphere
The background stratospheric sulfate layer is believed to be formed largely via the transport
of carbonyl sulfide (OCS) into the stratosphere, its subsequent conversion to H 2 SO 4
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