km from the surface of the earth. Figure 1 shows the altitude distribution of injectants from HLLV, and Table 3 gives the overall injection rates in each domain. To estimate the importance of a given injectant in a specific domain requires not just the injection rate and the ambient burden in the domain but also a characteristic residence time for the different injectants in the various domains. Some initial estimates of residence times are listed in Table 2. For water they are typically characteristic times for transport out of the domain (note the large effects of condensation!), while for NO where photochemical destruction of odd nitrogen (N, NO, NO2) is more rapid than transport, this sets the limit. In Domain C the energy equilibration time may be used, but here in particular there are large uncertainties because the phenomenology is not well understood (see Sections 4.3 and 4.4). Both the concepts and the numerical values must be examined and modified as necessary (see also Kellogg, 1964). Table 4 represents an initial attempt to describe the loading of the atmospheric injections in each domain in terms of a dimensionless "Perturbation Factor" or PF which is defined as pp _ (expected concentration change) (ambient concentration) In order to estimate a numerical value for the PF, some estimate of the expected concentration change resulting from the specified injection must be made. To lowest order, the concentration change may be estimated by the expression: (injection rate) x (residence time), in which the injection rate is given in units of mass/unit volume/unit time. An equivalent expression for the lowest-order PF is easily seen to be (total mass injection rate into domain) x (residence time in domain)/(total ambient loading in domain); this latter expression is used throughout the remainder of this report. The concept of a PF is useful in the limited context of suggesting the general areas in which problems may be expected. (Thus the same methodology shows that at altitudes below 70 km or so, only local rather than global effects may be expected; see Brubaker, 1979). Values of PF as large as a few percent indicate that effects of a given injection should be looked for, while PF values in excess of unity raise a warning flag. The detailed numerical values are generally not significant, partly because the numerical value of the characteristic or residence time is generally not well known and partly because details of the chemistry, etc., limit the applicability of the concept. (Thus we do not list separate PF values for 1^0 and I^.) The following points should be noted in connection with Tables 1-4: (a) The ambient loadings of injectants as used here are presented in Appendix D. (b) The atmospheric injections are large on an absolute scale because of the overall scale of a 5-GW SPS unit system, which corresponds to an orbital mass of 35,000-50,000 metric tons. Note that the overall effect of injectants tends to be significant on a global, rather than on a regional or local scale only above 75 km because of the very large mass of the lower atmosphere.
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