Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
Microphysics
The supersonic aircraft scenarios for 500 and 1,000 HSCTs are based on recent work (Baughcum and Henderson, 1998) carried out for the NASA technology concept
aircraft HSCT, which would cruise supersonically in the 17-20 km altitude range. The NASA subsonic scenarios described in Chapter 9 account for displacement of
subsonic air traffic by supersonic aircraft. Baseline computations assume supersonic aircraft emissions with EI(H2O)=1230 (1230 g H2O kg-1 fuel), EI(NOx )=5 (5 g NO2 kg-1 fuel), and a range of sulfate emission levels. Parametric studies were conducted around these baseline HSCT scenarios by investigating NOx emission index, fleet
size, flight altitude, and background atmospheric conditions. These parametric studies are appropriate because the technology of a commercially viable supersonic
airplane is not yet well-defined and results are needed to determine the sensitivity of the O 3 impact to the technology level. A description of each of the scenarios
evaluated by the participating models is given in Tables 4-4, 4-9, 4-10, 4-11, and 4-12. The HSCT scenarios use a number and letter designation preceded by the letter
S (e.g., the first scenario is S1a). HSCT scenarios contain subsonic aircraft as well as HSCT commercial aircraft, with the combination accounting for the same
passenger demand as in subsonic-only scenarios for 2015 and 2050. The HSCT scenarios in Tables 4-11 and 4-12 are generally analyzed relative to the
corresponding 2015 and 2050 base plus subsonic scenarios.
The effects of sulfur, NOx , H2O, CO, and NMHC (as CH4 ) are simulated in the scenarios. The treatment of sulfur emission is discussed later in this section. For the
other species, the aircraft effluents are put into the model as follows: Gridded fuel burn data (kg fuel/day) are first mapped into the model grid; the amount of material
emitted into each grid box is given by the product of the fuel burn and the EI; and the emitted material is put into the grid box at each time step with the equivalent rate.
In this approach, we ignore the effect of plume processing and assume that these emitted materials are instantaneously mixed into the grid box. This assumption is
probably valid in most of the stratosphere, though it may not be valid in the cold polar lower stratosphere during winter. In these regions, chemical processes are
strongly nonlinear, thus raising concerns about the assumption. To date there have been no detailed wake model calculations supporting or rejecting this assumption.
This important caveat should be remembered when considering the model results presented in this section.
Table 4-12: Percentage changes in total column ozone for each assessment model. The top value is for the Northern Hemisphere average; the bottom value is for the
Southern Hemisphere average. Source gas boundary conditions are for the year 2050. Model results have been rounded off to one significant figure for clarity.
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