Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
factors is presented in Table 4-3. Such regional differential factors are applied only to energy-related sources; biomass burning factors are applied as in the standard
case (using Table 4-2).
4.2.2.2. Aircraft Emission Scenarios
The 3-D aircraft scenarios described in Chapter 9 form the basis for the assessment. The scenarios evaluated by the participating models are summarized in Table 4-
4. Summaries of global emissions for these scenarios are given in Tables 9-4 and 9-5. Only a few scenarios are considered for subsonic assessment calculations
because computational requirements for the 3-D models are high. The subsonic scenarios in Table 4-4 are generally analyzed relative to corresponding background
atmospheres for 1992, 2015, or 2050.
In model calculations, aircraft effluents are put into the models 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 emission index. The emitted material is put into the grid box at each time step at the
equivalent rate. In this approach, we ignore the effect of plume processing and assume that emitted material is instantaneously mixed into the grid box. For the
subsonic assessment, NO x is the only aircraft emission considered. Because most models do not calculate the hydrological cycle in the troposphere, emitted water is
not calculated. Sulfur, CO, and unburned hydrocarbons are also ignored.
The basic scenarios examine some of the important aspects in understanding the calculated environmental impact of aircraft. However, a number of uncertainties
remain in the treatment of chemical and physical processes that may influence the effects from aircraft emissions. Therefore, a series of special sensitivity calculations
was designed to investigate the most important of the recognized uncertainties. The subsonic aircraft sensitivity scenarios, as described later, examine uncertainties in
the background atmosphere, the treatment of chemical and dynamical processes in the UT and LS, and different analyses of aircraft emissions.
It has not been possible (for practical reasons) for each of the modeling groups to run all of the scenarios set up for these 3-D model studies of aircraft perturbations.
Each modeling group has completed a limited number of model simulations.
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Table 4-4: Base background scenarios and subsonic aircraft scenarios.*
Model Scenarios
A 1992 Base (background atmosphere, no aircraft)
B
1992 Base + Subsonic Aircraft (Chapter 9, NASA
1992)
C 2015 Base (background atmosphere, no aircraft)
D
2015 Base + Subsonic Aircraft (Chapter 9, NASA
2015)
E 2050 Base (background atmosphere, no aircraft)
F 2050 Base + Subsonic Aircraft (Chapter 9, Fa1)