Causes and Effects of Stratospheric Ozone Reduction An Update (1982) / Chapter Skim
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1 CURRENT STATUS
1 CURRENT STATUS
Pages 15-34
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From page 15... ...
. To prepare our assessment, we relied on our professional knowledge, on a concurrent technical review prepared under the auspices of NASA, the Federal Aviation Administration, the National Oceanic and Atmospheric Administration, and the World Meteorological Organization (WMO)
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From page 16... ...
Process II summarizes reaction schemes in which atomic oxygen is not limiting, for example, OH + O3 ~ HO2 + O2 HO2 + O3 ~ OH + 2O2.
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From page 17... ...
. About 1 percent of stratospheric ozone, 600 million metric tons per year, is removed below 25 km by process II, with a similar amount being lost by physical transport to the troposphere.
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From page 18... ...
18 / ////.4 I ~ o i' I .~°, ~ o ° o ~ on' I 1 1 1 1 to I o I ~ = 1 ~ ~gag \ \ C ~ \ ~ o \ lo, £= \ \ i\ C To ',o:, \ / ,Y,0~t / : ~/ / / / Ads' :~ 1 v.
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From page 19... ...
Current theoretical models lead us to conclude that the dependence of ozone concentration on altitude will also change, the net effect being a redistribution of ozone from higher to lower altitudes. Quantitative estimates of these effects have varied somewhat over the past decade (Appendix A)
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From page 20... ...
Calculations now indicate that the reduction would occur almost entirely at altitudes above 35 km, in the region of the stratosphere where the ozone concentration is determined primarily by chemical processes, with a smaller, partially compensating increase in ozone concentrations at lower altitudes. The current result obtains for both 1- and 2-dimensional models and further differs from that prevalent in 1979 in that earlier calculations showed regions of reduction both above and below 35 km.
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From page 21... ...
Results of model calculations using current values for these reaction rates are in good agreement with observations of C1O for altitudes below 35 km (Appendixes C and D) , whereas models using the reaction rates favored in 1979 give concentrations of C1O a factor of 3 higher than observed values in this range.
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From page 22... ...
A source of NOX at lower altitude, associated for example with subsonic commercial aviation, can modify local chemistry such as to cause an increase in tropospheric ozone. It has been suggested that reductions in the column of ozone above the earth's surface due to reductions in stratospheric ozone may be masked to some extent by increases in tropospheric ozone attributable to subsonic jets and urban smog.
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From page 23... ...
Current models incorporating this effect suggest that the steady state reduction in total ozone due to continuing emissions of CFCs at 1977 rates would change from 5 percent to 9 percent to between 4 percent and 6 percent if global CO2 were doubled concurrently (Hudson et al.
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From page 24... ...
Similarly, agreement between modeling results and observation of C10, while encouraging, need not imply validity of the model at lower altitudes. The improved agreement between observed and calculated concentrations of C10 in the lower stratosphere may be attributed mainly to changes in rate constants for reactions affecting OH.
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From page 25... ...
the reaction schemes incor data on environmental other parameters, and porated into the model. There are still uncertainties about the appropriateness of some assumptions common in current models.
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. As detailed in Appendix A, total column ozone fluctuates on a variety of spatial and temporal scales owing to natural causes; these fluctuations tend to mask possible systematic changes due to man-made perturbations.
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From page 27... ...
. Since, however, the reduction due to CFCs is expected to be concentrated at high altitudes, measurements of total column ozone are less sensitive indicators of an anthropogenic effect than are measurements of ozone profiles.
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From page 28... ...
Such estimates employ professional judgments about the importance of various factors and the sensitivity of the results to potential changes in understanding. Our major concern in estimating uncertainties in our understanding of stratospheric ozone is with the possibility that some key process or processes may be missing from current models.
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From page 29... ...
As stated earlier, a representative estimate of potential steady state reduction of global ozone due to continued releases of CFCs at the 1977 rate in the absence of other perturbations is 7 percent. There continue to be, however, important discrepancies between theory and observation.
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From page 30... ...
2. The concern regarding the possibility of reduction e in stratospheric ozone due to CFCS remains, although current estimates for the effect are lower than results given in NRC (1979b)
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From page 31... ...
If, however, the concentrations of N2O in the atmosphere were to double, in the absence of other perturbations, current models suggest that the steady state reduction in the total ozone would be between 10 percent and 16 percent.
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From page 32... ...
The national research program, including atmospheric observations, laboratory measurements, and theoretical modeling, should maintain a broad perspective with some focus on areas of discrepancy between theory and observation. A coordinated research program to understand the spatial and temporal distributions of key species and radicals merits highest priority.
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From page 33... ...
Models should be developed to describe the combined effects on stratospheric ozone of future changes in releases of all relevant gases, such as CFCs, N2O, CO2, CB4, CH3C1, and CH3CC13.
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