Causes and Effects of Stratospheric Ozone Reduction An Update (1982) / Chapter Skim
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C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY
C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY
Pages 167-205
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From page 167... ...
Second, the chemistry of the system is very complex, involving labile species at low concentrations subject to transport processes that are not well understood. These difficulties force us to rely on simulations using theoretical models to assess possible perturbations to stratospheric ozone.
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From page 168... ...
These discrepancies may be attributed to inaccurate values for kinetic data affecting calculation of the concentration of the OH radical. Below 25 km, NO and NO2 are controlled by chemical exchange with HNO3, the major odd-nitrogen species, with the main reactions being NO2 + OH + M ~ HNO3 + M HNO3 + he ~ NO2 + OH NO2 + he ~ NO + O NO + O3 ~ NO2 + O2 Nitrogen dioxide and nitric oxide concentrations thus vary inversely as the concentration of OH, (1)
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From page 169... ...
pointed out that model and observations could be brought into agreement if it was assumed that the model overestimated the concentrations of OH, and they noted that such an error could strongly affect estimates quoted in NRC (1979) for the response of ozone to enhanced levels of stratospheric chlorine or odd nitrogen.
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From page 170... ...
1978) using kinetic data from Hudson et al.
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From page 172... ...
The labels 1979, 1980, and 1981 indicate rate constant sets shown in Table C.1 (Hudson and Reed 1979, NASA 1981, and Hudson et al. 1982, respectively)
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From page 174... ...
Slow recombination reactions are difficult to study in the laboratory, especially for stratospheric temperatures and pressures, and the future may well hold further chemical surprises in this area. The present set of reaction rate data brings calculations and observations into reasonably close agreement below 30 km, as shown in Figures C.3, C.4, and C.5 for OH, HNO3, NO2, NO, O
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From page 175... ...
. Calculations are appropriate for 30°N latitude at equinox and for solar zenith angles and local times as indicated.
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From page 176... ...
'& 9 fEB 1977 Visible Absorption ~Goldman et al (1978) - 35 a 10 OCT 1979 IR Absorption Blatherwick et al ( 1980)
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From page 179... ...
Mean profles for summer and winter are derived from the measurements shown in Figure C.4, and calculated profiles are from the two-dimensional model of Ko and Sze (see Hudson et al.
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From page 180... ...
The twodimensional model of Ko and Sze is used for comparison with seasonal variations. Present models agree very well with summer observations of C10 in the key region between 25 and 35 km, but there may be significant disagreement at 40 km.
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From page 181... ...
and (c) Rates for production and loss of odd oxygen calculated using rate constant sets from Hudson and Reed (1979)
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From page 182... ...
\ \ \ i ~ 1981/ j 1979 Aft 2 {HO2+03~__ / l l l ~ ~ of odd-O b ~it' ~ Loss of odd-O , 4-, ,,,1 , i ~,~,,1 , ,,,,, 11 4 105 REACTION RATE (cm~3 sec~1 )
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From page 183... ...
Loss profiles for odd oxygen obtained with the best rate data of 1979 (Hudson and Reed 1979) were significantly different from those shown in Figure C.6a, as may be seen in Figures C.6b and C.6c (see also Table C.1)
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From page 184... ...
in stratospheric chemistry seems much of what we know about strato inconsistent with spheric ozone. Global Distribution and Balance of Ozone It has been known for some time that long-lived tracers in the lower stratosphere tend to be distributed along surfaces of preferred mixing that slant downward from equator to pole.
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From page 185... ...
Note that a given mixing surface intersects a wide range of chemical lifetimes for ozone, with short lifetimes at low latitudes and long lifetimes at high latitudes.
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From page 186... ...
. Inspection of Figure C.7b shows that, in the lower stratosphere, ozone behaves as a passive tracer and is uniformly distributed along the isopleths shown in Figure C.7a.
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From page 187... ...
This conclusion will prove to be quite useful in our discussion of model simulations for perturbed conditions. Ozone Response to Environmental Change Figure C.8 shows calculated reductions of stratospheric ozone due to increased atmospheric burdens of chlorofluoromethanes (CFMs, Figure C.8a)
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From page 188... ...
calculated using the Harvard one-dimensional model. Results are shown for (a)
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From page 189... ...
189 s 4 LIJ ~ 3 I ~ ~ / 2x [N2O] 1981 roses / / ° /\;O3d3=-15% / , / _ cool / 1 11 1 1 1 1 1 1 1 1 1 20 I ~ ~ ~ ~ : ~)
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From page 190... ...
Using 1979 rates, the calculation in the transition zone is quite sensitive to the treatment o f transport processes and depends on a complex set of reactions involving ClNO3. As chlorine is added to the lower stratosphere, formation of ClNO3 removes increasing quantities of NO, NO2, and HNO3.
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From page 191... ...
In both cases the difference is due to the ozone response in the transition zone, and in both cases the results obtained with 1981 rates are less sensitive than the 1979 model to details of the transport parameterization. We argued above that the 1979 rate set produced spurious chemical losses for O3 in the lower stratosphere; we now see that these loss processes distorted the calculated response of ozone to environmental change.
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From page 192... ...
in the lower stratosphere. Since models predict excessive NO2 at high latitudes, especially during winter, ozone reduction by NOk is probably overestimated above 30° latitude.
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From page 193... ...
The dispersion rates in the two-dimensional models are evidently large enough to ensure nearly perfect mixing along the preferred surfaces. Observations are compared in Figure C.ll to model results for CH4, N2O, CF2C12, CH3C1, CFC13, and C 2H6.
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From page 194... ...
Mi Her et al. , , ,,, , , , ,,,, ~ 1 , , 45°( ~ ~ ~ <~> m.1 ,~ ~ 11 lo lo CF2 Ct2 (mole fraction)
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From page 195... ...
44°N · 6/7/77 · 6/16/77 · 9/9/77 · 9/26/77 \ ~ W, ~No N5* ~ Wo _ to j of taco 1 x 1.0 1.5 FIGURE C.11 Model results for (a)
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From page 196... ...
. ~11 lo-lo CF2 Ct2 (mole fraction)
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From page 197... ...
,o I i I I I I I I I I l I ! I I I I I l l I l l I l I ~11 lo-lo CH3C~ MOLE FRACTION FIGURE C.11 (Continued)
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From page 198... ...
O 1 1_ 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 , 1 lo-12 10-11 . I 1 1 1 11 1 ~, 1 1 1 ~I I lo-lo C2H6 MOLE FRACTION FIGURE C.ll (Continued)
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From page 199... ...
The models all appear to underestimate the rates for photolytic destruction of these gases in the lower stratosphere, leading to excessive concentra Lions at all latitudes and to an overestimate of global mean lifetimes. The models consequently predict excessive concentrations of chlorine, at steady state, in response to long-term industrial release.
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From page 200... ...
Models predict that stratospheric ozone should decline by about 6 percent as the stratospheric chlorine concentration increases from current levels (3 ppb) to the asymptotic level (11 ppb)
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From page 201... ...
Nitric oxide mixing ratios near the stratopause measured by a rocket-borne chemiluminescent detector. Geophysical Research Letters 5:1023-1026.
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From page 202... ...
Implications of low stratospheric hydroxyl concentrations for CFM and SST scenario calculations of ozone depletion. EOS Transactions of the American Geophysical Union 59:1078.
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From page 203... ...
(1980) Sources and sinks for nitrous oxide Pages 345-364, Proceedings of the NATO Advanced Study Institute on Atmospheric Ozone: Its Variation and Human Influences, edited by A.C.
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From page 204... ...
Production of atmospheric nitrous oxide by combustion. Geophysical Research Letters 3:751-753.
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From page 205... ...
Production of nitrous oxide in the auroral D and E regions. Nature 287:525-526.
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