calculations with the 1-D model that for the globally averaged case, indicate that the CO abundance would be increased by less than 10%, with no effect on the distributions of other constituents. Sulfur Dioxide It has been estimated (K. L. Brubaker, Argonne National Laboratory, private communication, 1980) that the first-stage fuel of the HLLV could contain 0.05% sulfur by mass. The yearly deposition of sulfur dioxide in the stratosphere is therefore estimated to be about 200 tonnes yr-1 (220 tons yr-1) or less, as compared with an estimated ~ x 105 tonnes yr-1 (1 x 105 tons yr-1) of SO2 produced in the stratosphere from COS of tropospheric origin (41). Based on the work reported by Turco et al. (41), we estimate that the resulting fractional increase in the mass concentration of the stratospheric aerosol layer would be negligible and not affect Earth's albedo and mean surface temperature. 5. PERTURBATIONS TO ODD-OXYGEN AND ODD-HYDROGEN The computed accumulations of excess water vapor and nitric oxide lead to predicted changes in the distribution of odd-oxygen and odd-hydrogen (HOJ species. The odd-hydrogen concentration is enhanced mainly through the reactions where water vapor photolysis occurs at high altitudes [above 70 km (43 mi)]. The odd-hydrogen generated is distributed among several species, including H, OH, HO2, and, at low altitudes, H2O2 and HNO3. Our computations show that the increases in HOj. abundances are significant only in the mesosphere and thermosphere; in the stratosphere, concentrations of OH and HO2 increase only about 0.5% at 50 km (31 mi), and decrease with descending altitude. Of course, such stratospheric perturbations will influence the ozone column density somewhat, as is discussed below. Figure 11 shows computed absolute increases in HOX species concentrations. The calculations were carried out with the 1-D model for globally averaged conditions, which are close to the 2-D results. In the region near the mesopause, excess injected atomic hydrogen may influence the thermal balance. The chemiluminescent reaction with ozone, would enhance hydroxyl (Meinel) vibrational band emission and cool the atmosphere. More importantly, hydrogen catalyzes odd-oxygen recombination through reaction 30 followed by The net reaction cycle releases as heat the chemical energy in atomic oxygen, providing an additional local heating source. We have not been able to quantitatively assess
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