with the result that the trail undergoes rapid dispersal to concentrations approaching ambient values. The effect of such large NO enhancements on ionospheric structure will be discussed elsewhere. Carbon Dioxide and Carbon Monoxide The first stage of the HLLV bums methane fuel and carbon dioxide is a principal product of combustion. Since the methane molecule contains carbon and hydrogen atoms in the ratio of 1 to 4, assuming stoichiometric combustion, one expects the volume rate of CO2 emission to be one-half that of water vapor at altitudes below 56 km (35 mi). Actually, according to Ref. 1, the combustion is not stoichiometric; the CO2 volume emission rate is about 0.4 that of water vapor and that for CO is about 0.3 that for water (1). Although CO2 deposition ceases at an altitude of 56 km (35 mi), it is effectively mixed upward from that height; diffusion to the troposphere is a slower process. As a result, the absolute increase in the CO2 content should roughly approximately one-half that for water vapor. Figure 10 shows the computed change in the mixing ratio of CO2 for several altitudes. The increase in the mixing ratio of CO2 at an altitude of 50 km (31 mi) ranges from about 3 x 10“3 ppmv to about 7 x 10-3 ppmv, which should be compared with the mixing ratio in the ambient atmosphere of ~300 ppmv. The fractional change is only about 1 to 2 parts in 105,
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