FIGURE 12.9 Calculated percent change in total column ozone during March as a function of latitude due to a Mach 2.4 HSCT fleet from the three models for which results were shown in Fig. 12.7, assuming NOA. emission radiation of 5 g of N02/kg of fuel. These are the predicted changes due to the projected HSCT fleet compared to a projected solely subsonic fleet (adapted from Stolarski et al, 1995).

12.7. Small changes are predicted by all models in the tropics, but larger changes poleward, up to ~0.5%. Much larger changes, approaching 1.7%, are predicted if the EINO is 15.

An assessment of the effects of HSCTs on stratospheric ozone is given by Stolarski et al. (1995), and the interactions between NOx and C10x cycles at various concentrations are treated by Kinnison et al. (1988), Johnston et al. (1989), and Considine et al. (1995). A discussion of some of the general issues involved in the development and possible future use of the HSCT is found in Zurer (1995).

2. Space Shuttle and Solid Rocket Motors

The launch of the space shuttle and other vehicles such as the Titan launch vehicles results in emissions directly into the troposphere and the stratosophere. Exhaust emissions include A1203 (30% by weight), CO (24%), HC1 (21%), H20 (10%), N2 (9%), C02 (4%), and H2 (2%) (Danilin, 1993).

The major focus on the effects of exhaust emissions has been on the HC1 component and its role in ozone depletion and on the A1203 particles, which could provide a surface for the heterogeneous conversion of HC1 to active forms of chlorine. It has been proposed that if the HC1 were converted to photochemically active forms relatively rapidly, a mini "ozone hole" could form in the flight path of the vehicle (Aftergood, 1991; McPeters et al., 1991; Karol et al., 1992).

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