CHEMICAL EFFECTS OF THE HLLV INJECTION OF WATER INTO THE ATMOSPHERE Some of the water vapor deposited in the atmosphere by the HLLV is converted to molecular hydrogen in the mesosphere, mainly through the reaction sequence (See also Ref. 1.) The odd-hydrogen (HOJ is distributed among H, OH, and HO2 species as indicated above, but also appears as H2O2 and HNO3 in the stratosphere. Our computations show that the increases in HOj. abundances are significant only in the mesosphere and thermosphere; in the stratosphere, calculated increases in OH and HO2 are only 0.5% at 50 km and decrease with descending altitude. The principal effect of the increase in HO^. abundance is to reduce atomic oxygen in the mesosphere and ozone in the stratosphere through the catalytic reaction sequences: in the upper stratosphere. Model calculations of the changes in species abundances caused by the injection of water vapor are shown in Fig. 7 for O(3P), O3, OH, and HO. From Fig. 7 it can be seen that the abundances are predicted to change by 20% or more at and above 80 km. Since the changes in these abundances depend on the magnitude of the water vapor increase, these species are also predicted to exhibit a corridor effect. UNCERTAINTIES IN THE TRANSPORT PARAMETERIZATION It is clear from Eqs. 7 and 9 that the reliability of the estimates of the minimum injection rates required to produce a corridor effect depend on the reliability and appropriateness of the transport coefficients. In order to obtain reliable zonal averages, observations over a long period of time taken at frequent intervals in time and space are required. Because of the difficulty and expense of making measurements above 60 km, little or no zonally averaged data exist. Consequently, the values of the
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