corresponds to well under 1% in the altitude range of 30 to 40 km and even less at lower altitudes. Most of the ozone in me atmosphere is located between about 23 and 35 km. These water vapor injections are unlikely to have any direct effect on the ozone content as a whole. However, they will be concentrated at the latitude of the launch site, and the consequences of this localization are being explored. TABLE 30 SHUTTLE VEHICLE WATER VAPOR INJECTION INTO THE STRATOSPHERE (360 LAUNCHES/YEAR) The percentage increment in water vapor is large in the highest region of the stratosphere near 50 km, due to the fact that the atmosphere is extremely thin and consequently its -total water content is low, even though the mixing ratio is about twice that observed at lower levels. The chemistry of water vapor in the upper stratosphere has been studied but there is great uncertainty regarding the possible consequences of increments in water vapor on the order of 2%. Water vapor is photodissociated to form hydrogen, hydroxyl, and hydroperoxyl radicals and hydrogen peroxide molecules which will react with ozone, and molecular and atomic oxygen. The latter constituent is abundant at this level. Since some of the NOX at lower levels is produced in the mesosphere and carried downward through the region in question, it is conceivable that changes in the water vapor content will influence the natural tlux of NO* to the level of the ozone layer. Booster engines using solid fuel are employed for two minutes after launch. These burn a total of 2.2x106 pounds of propellant in the two-minute period, generating exhaust which is 24% CO, 22% HC1, 10% H2O, 30% A12O3, 9% N2, plus small amounts of CO2 and H2. The water generated by these boosters is being considered in the atmospheric-effect study program now under way. According to Martell (55), vertical eddy mixing is very rapid throughout the mesosphere (50 to 80 km) and the lower thermosphere (80 to 100 km) and for this reason the effect of water vapor emissions in these regions has not been calculated. The region of the atmosphere from the stratopause to 100 km in altitude contains only 0.1% of the total mass of the atmosphere, or about 5x10'8 grams.
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