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Causes and Effects of Stratospheric Ozone Reduction: An Update (1982)

Chapter: C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY

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Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
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Page 167
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
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Page 168
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
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Page 169
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
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Page 170
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
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Page 171
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
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Page 172
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
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Page 173
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
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Page 174
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
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Page 175
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
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Page 176
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
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Page 177
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
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Page 178
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
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Page 179
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
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Page 180
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
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Page 181
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
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Page 182
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
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Page 183
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
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Page 184
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
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Page 185
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
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Page 186
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
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Page 187
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
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Page 188
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
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Page 189
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
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Page 190
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
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Page 191
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
×
Page 192
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
×
Page 193
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
×
Page 194
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
×
Page 195
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
×
Page 196
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
×
Page 197
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
×
Page 198
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
×
Page 199
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
×
Page 200
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
×
Page 201
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
×
Page 202
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
×
Page 203
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
×
Page 204
Suggested Citation:"C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY." National Research Council. 1982. Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, DC: The National Academies Press. doi: 10.17226/319.
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Page 205

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Appendix C RECENT DEVELOPMENTS IN STRATOSPHERIC PHOTOCHEMISTRY Steven C. Wofsy and Jennifer A. Logan Division of Applied Sciences Harvard University INTRODUCTION Studies of the stratospheric ozone layer are impeded by two characteristics common to many environmental ques- tions. First, it is impossible to perform meaningful, controlled experiments to test the response of the system to changes in environmental parameters. 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. The models are inevitably too simple to describe the complete physical system and yet are often so complicated that it may be quite difficult to understand the models and to draw model-independent conclusions from the results. This paper examines recent models of stratospheric ozone and associated chemical species, with emphasis on developments subsequent to the earlier NRC study on the stratosphere (NRC 1979). The discussion relies primarily on calculations performed using our own one-dimensional model of the stratosphere (Logan et al. 1978, Wofsy 1978) and on results from two recent two-dimensional models (Miller et al. 1981; Steed et al. 1982; Ko, Sze, and co-workers reported in Hudson et al. 1982). This choice reflects our access to model results and our view that these models contain most of the essential features of other operational models. 167

168 EFFECTS OF NEW KINETIC DATA ON MODEL RESULTS Species Concentrations Stratospheric models in use during the previous NRC study (NRC 1979) appeared to underestimate by a factor of between 2 and 5 concentrations of NO and NO2 below 25 km, and to overestimate the concentration of C10 by a factor exceeding 10 at the same altitudes. 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) (2) (3) (4) [NO2] ~ J2[HNO3] (5a) kl[M] [OH] [NO] ~ J2[HNO3] J3 1 (5b) kl[M] k4[O3] [OH] where [x] denotes the concentration of species x and ki(Ji) refers to the rate coefficient (photolysis rate) for the ith chemical reaction. The concentration of C10 also is controlled by inter- change with a more abundant species, HC1, but in this case C10 increases with OH. The principal reactions are HC1 + OH ~ H2O + C1(6) C1 + O3 + C10 + O2 C1 + CH4, H2, H2CO ~ HC1 + CH3, H. HC(8-10) C10 + NO ~ C1 + NO2,(11 ) which lead to the expression

169 C10 ~ ~ [OH]2 k6[HCl] [OH]k7[O3] {k8 [CH4]+kg [H2] +klo [H2CO]}kll[NO] k6[HCl]k4k7[O3] kl[M] {k8 [CH4] +kg [H2]+klo [H2CO]}kllJ3J2 [HNO3] (12a) (12b) Hence [C10] increases as [OH] 2. McConnell and Evans (1978) 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. New laboratory measurements lend support to the hypothesis advanced by McConnell and Evans (1978) and others (Turco et al. 1981). Wine et al. (1981) and Nelson et al. (1981) showed that the rate for the reaction OH + HNO3 ~ H2O + NO3 (13) increases at low temperature. This reaction is the major sink for odd hydrogen below 25 km, as shown in Figure C.1. Rates for reactions involving peroxynitric acid (HOONO2 or HNO4) have also been revised recently as shown in Table C.1. Rates for formation of HNO4 and for reaction between OH and HNO4 appear to be faster than formerly believed, HO2 + NO2 + M ~ HNO4 + M HNO4 + OH ~ H2O + products (14) (IS) (NASA 1981, Littlejohn and Johnston 1980, see also Hudson et al. 1982), whereas photolysis of HNO4 may be slower than indicated by earlier studies, HNO4 + hv ~ products (Molina and Molina 1981). These results, further work, indicate that reaction (15) pathway for loss of odd hydrogen ~ (16) if confirmed by is a ma~or (see F~gure C.1). Figure C.2 shows how calculated profiles for OH, HO2, C10, NO, and NO2 (at noon) have changed in response to the new laboratory rate data. Model concentrations of OH have been lowered by about a factor of 3 at 20 km, NO and NO2 have been increased by a

170 50 . 45 40 E - 35 a 1 1 1 1 1 1 1 1 1- 1 -W-I 1 1 1 1 ~1 W- ~1 1 1 1 1 11 ' ~ \ OH + HNO3 V- OH + H202 HO2+0H \ -it\ \ 30 25 20 15 - \ me,, i,: OH + HNO4 / \ / ~ / O H + H NO4 /~/ I ~t l l l ,/ /~OH+HNO3 .. 1. 1 l,__ I I_I I I I I LL L_ . 2 103 104 RATE ( cm~3 sect ) FIGURE C.1 Rates for loss of odd hydrogen, averaged over a 24-hour period. Profiles are shown for 30°N latitude at equinox. Results are from the Harvard one-dimensional model (Logan et al. 1978) using kinetic data from Hudson et al. (1982~.

171 Ct Q.) 00 Ct ~ ~ _ ._ ~ Ct _ a~ ~ C~ _ o ._ C~ o ·_. C) C~ e~ C~ o Ct o ._ C~ Ct C: m V' l £ C) C~ - c) ~o o C) Ct C~ 4 - _~ o ~ _ _ oo _ ¢ ¢ Z o o%\ ~ - _ _' . . . ~ oo o C~ ~ X X X X X _ 1 ° 1 ~o ~o _ ~ _ C~ C~ X ~ X o °. o °. o' s:L X _ _ 1 1 o o _ _ C~ o - ~_ x - 1 o _ C~ X X ~ X ~ °. o _ oo _ _ 1 1 o o _ _ - o _, x - 1 o o _ _ XX XX ~ oo o . .. . oo ~ ~ ~t _ C o ~ ° + O ~ ~ O ° ~ Z + O ~ ~0 Z O ~0 ~ X ° + + Ze'+ + :r 5: 0 := ~ O O ~ O O ~_ - 00 . _ ~ C~ _ _ 0 . _ ~ Ct C~ £ ~ == ~o C~ ~Q

172 55 50 45 - ~ 40 5 Hi: 30 25 _ 20 1 , 1~,,l/ 1 1/1 , lo6 a 107 55 50 45 40 535 30 25 20 ... . 1_ ~ .~_~11 I i ~__,_, 1 ,, ~1-~1 I,,, 105 1o6 10 ~ CtO (cm~3) C 1 1 1 1 1 1 1 11 1 1 1 1 1 1 1 11 81~\\ I r--r- I l-r-~-~---r--~ I I i l: 80 \ 81479 lo8 lo6 ) . // 1 ~ 111111 1 10' b 1 1 ~1 1 1 - 1- - - 1 1 1 1 -rams ~- ~I 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1o6 ~\,,,1979 1981 Slow CIO+N,~ ~ ~1980 fit/ 8 109 FIGURE C.2 Altitude profiles for (a) HO2, (b) OH, (c) C1O, (d) NO and NO2 at noon. 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). lo8

173 ' ' ''''4 '' ' ' '''''I ' 1 40 30 20 40 Y 30 LLJ C) ~ 20 NO2 _ , _ - - 1 1 - d 10 107 .~ 'it ) 1979,~' / 1981 1 1 1 1 1~x NO 1 !\ ,- I lo8 NUMBER DENSITY (cm) FIGURE C.2 (Continued) 109

174 . . . similar factor, and calculated C1O concentrations have decreased by nearly a factor of 10. It may seem surprising that relatively modest changes in the rates for (13) through (16) should have such dramatic effects on calculated profiles for OH. Chemical interchange among BOX radicals is quite rapid in the lower stratosphere, with lifetimes for HO2 and OH at noon about 50 and 10 s, respectively. The fast reactions establish the ratio of [OH] to [HO2], but radical production and loss reactions control the absolute concentrations. Recombination reactions for HOX radicals are inefficient in the lower stratosphere, such that the chemical lifetime for the sum of HO2, H. and OH exceeds 500 s (see Figures C.1 and C.2). Hence slow processes such as (13) and (15) can exert a major influence on the composition of the stratosphere. 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 calcula- tions 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. and C1O. The figures also illustrate the relatively poor agreement obtained by using the 1979 rate data. Unfortunately, the comparison is not yet definitive. Data on OH and O are nonexistent below 30 km, and few simultaneous observations are avail- able for NO, NO2, and HNO3. The vertical gradient for NO does not coincide very well with observations by Ridley and co-workers (Ridley and Schiff 1981, Ridley and Hastie 1981) (Figure C.3d) but does agree with data obtained by Horvath and Mason (1978) (see also Hudson et al. 1982) (Figure C.3c). The model predicts more HNO3 than is observed between 25 and 30 km. The apparent discrepancy observed for O (Figure C.3f) at low altitude may be attributed to differences for [O3] and local albedo between the model and the particular observations. The model does predict accurate values of the ratio [O]/[O3], as shown in Figure C.3g. Observations of C1O require special consideration. Reported measurements are shown in Figure C.4 (Weinstock et al. 1981, Anderson et al. 1980). Summer data (solar declination of >0) fall in a rather narrow band, as predicted by the model, except for anomalous results obtained on June 15, 1979, and July 14, 1977. (The anomalous Bastille Day profile (July 14, 1977, Anderson

175 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 70: LLJ 60 _ ~ _ SO-SO _ 4Sr _ - a ~_ 40 1 , 1 , 1 1 1 1 1 J 1 1 1 1 1 6 10t OH CONCENTRATION (cm~3) 1 1 1 1 1 1 1 1 BAllOON-BORNE IN SITU · 12 Jan 1976 ( x2) x 80° ~40-~ 26 Apr 1977(x2)x.80° i Y ° 14 JuI 1977,x 41° 35 :~:~ 107 OH CONCENTRATION (cm~3) I i lo8 1 I ~ 30 lo6 1 111 lo8 FIGURE C.3 Model results for OH in the (a) upper and (b) middle stratosphere; (c) HNO3; (d) NO2; NO in the (e) lower and (I) upper stratosphere; (g) 0(3P); and O [O] / [O3 ] compared with measurements. The measurements are presented and discussed in Hudson et al. (1982). Calculations are appropriate for 30°N latitude at equinox and for solar zenith angles and local times as indicated.

176 45 35 30 25: ! 50 45 40 1 1 1 1 1 1 1 11 1 ,1 1 1 1 1 111 1 1 1 1 1 i 1i fischer (1980) HNO _ 0 May 1979 - 31 °N 3 O Feb 19?9-31°N \ :cicu/oted MlOlATITUDES Arno~d eto~ (1980) 0 ~ ,' NORTH _* Nov 1977-45°N * \ Evans et al (1978) ~\ · Jul-Aug 74-76 51°N ~0 v)\ _ Harries et al. (1976) 5 ~ 0\ 0 Sept 1974-45°N 3Vo \ Fontanellc etal (1975) O- ~ \O| · Ju~ 1973-48°N 0310- Murcray et c~. (1980) ~ ~i j v Oct 1979-32°N O=/~| 20- L zrus and Gandrua(1974) ~ 8 r~nc 1971 0 0 ~ii ~ 0 0 SPring 1971 I O SPring 1972 0 c 15r 0 SPring 1973 ~32°N 101 1 1 1 1 1 1 1 ! 1 1 1 1 1 11611 1 1 1 1 1 1 1 1 1 1 ! ! ! ! ! ! 0.1 1 10 MlXiNG RATIO (ppbv) VERTICAl COlUMN I 11 to40km (86 ~ 4.0)x1o15cm~ 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 SUNSET 32-33°N - MURCRAY ~ COWORKERS x ° 7 DEC 1967 IR Absorption - Murcray et al (1974) '& 9 fEB 1977 Visible Absorption ~Goldman et al (1978) - 35 a 10 OCT 1979 IR Absorption Blatherwick et al ( 1980) 30- flSCHER ~ COWORKERS (1980) ~: 1 25 20 O 9 fEB 79 ~ Visi ble Absorption -~ 5 MAY 79' - NO? 15 1 1 1 1 1 llll 1 , 71° 86° 94° ~/ o ~/ ~ / d 1 11 1 111 1 1 1 11 1111 1 1 1 1 1 1 11 0.1 1 10 M IXI NG RATIO ( ppbv) FIGURE C.3 (Continued)

177 451 1 1 1 1 1 iIII 1 1 1 1 tIIiI 1 1 1 1 1 IiII 1 i i RII)I fY ~ COWORKERS 25 l 15- ... . 40-~ 25 OCT 1977 32°N S5-75° e 12 DEC 1977 34°S 75-533 35 _ ~ 14 DEC 1977 34°S 75-53° v 30 OCT 1978 32°N 53-69° I o 8 NOV 1978 32°N 55-75° ~, 301 ~12 AUG 1978 51°N 54-57° ~I 251 5 1 ~ 20' oO' - v ;~- ~ N O 4~ ..' 1 1 1 1 1 1 1 1 1 1 1 ! 1 1 1 1 1 1 1 1 1 1 101 1 1 1 1 1 1111 ~ 0.1 1 10 MIXING RATIO (ppbv) 1 e 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 60 55 45 40 35 30 25 HORVATH ~ MASON x -° 8 APR 1975 39°N 41° o 19 MAR 1976 39°N 49° _ 0 14 JUl 1980 39°N 16° 16 OCT 1980 39°N 61° NO oo o \~X-71° o o \ o~ o od o o~^ 0 o~,o aO o) o o ,`70 / ~/ o i~1 ~ ~ ~ ~ ~ ~ ~1 ~ ~ ~ ~ ~1 ~ ~ ~ ~ l, f 0.1 1 10 MIXING RATIO (ppbv) FIGURE C.3 (Continued)

178 44 40 ~I,,, , , , , , I ·,, I i, , . . · ~ . ~ . · 6-15-79 10-25-77 x 1 1- 17-78 _ _ i 36 x:/ _ o _ /: t ~ MM ER _ 28 ,~^, ~ 1/,/61 1 1,, 1 1,,1 1 , ... ... 107 1o8 109 1 [0(3P)3 (cm-3) 42, 38 Y _ _ _ LL _ _ 34 _ J 30 - · 2 DEC 1977 _ X = 50° _ X =32°N _ ~ MODELED _ ~ X I I I I II I I I I I - h 10 5 10-4- 10-3 10-2 RATIO [O] / [03] FIGURE C.3 (Continued) 1010

179 · 12-8-76 · 12-2-11 · 10- 25-77 · 1 1- 16-78 - SUMMER AND FAll 40 35 30 25 2 0 i _~ _ ~1 1 ~ _ L_1_1 1 1 1 1 ~1 1 111 1 107 lo8 10 o o o o o o 0 0 O nA O x o~ 00 +^ x xo 0 0 OX + O< 0 + O x O + ox ~o +OX~ fox ~ox 3+ x 00 X X X o + 6-1-78 ° 6 15-79 O 9-26-77 LATE FALL CtO (cm~3) · · · ·.. · . . ~ ~ - · ~ ·. - .. A; _ ~ lo8 FIGURE C.4 Measurements of C10 concentration by in situ resonance fluorescence (Anderson et al. 1980~. 45 40 - LIJ c~ 35 _ ct 30 _ 25 '1'1~1~1 1 1 1 1 1 - Summer/f~ll (colc) ~/ \` ~ 1, ' W~ 7~/7y ~ / ~ /J / Winter (colc)~< ': 35 30 est. from dota Ko ~ Sze; ,: Q~ ~ 20 1 1 1 , 1 ,,I, 107 lo8 C ~ O cm~3 25 20 ~,,,~0,1 , ,,,,1 o.S 1.0 R= Summer/winter FIGURE C.S Seasonal variations of C10 concentration. 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. 1982~.

180 et al. 1980) is not shown in Figure C.4). Data from late fall or early winter (X < -10°) are scattered more widely and are lower than summer data. Figure C.S shows mean profiles for summer and early winter. The two- dimensional 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. The calculated seasonal variation appears to be qualitatively correct (Figure C.5), although the winter values in the model may be too high by a factor between 1.5 and 2. The concentrations of NO and O3 in the model are of major importance in this regard, since below 30 km [C10] varies as [O3]/[NO] (see equation (10)). Present models may overestimate the concentration of NO in the winter stratosphere, as discussed below, and this error may be the cause of the discrepancy in C10 during winter. - Rates for Catalytic Cycles Figure,C.6a shows calculated profiles for rates of reactions that destroy odd oxygen (i.e., O and O3) in the stratosphere. Recombination of odd oxygen by C10 and NO2 proceeds through catalytic cycles, as shown by the following reaction sequences: NO + O3 + NO2 + O2 NO2 + O ~ NO + O2 (17) (18) O3 + 0 ~ 2O2 (net); C1 + O3 ~ C10 + O2 (19) C10 + O ~ C1 + O2 (20) O3 + 0 ~ 2O2 (net) e Both sequence (17) and (18) and sequence (19) and (20) represent homogenous catalysis of the reaction originally proposed by Chapman (1930) for recombination of O and O3 in the stratosphere, O + O3 ~ 2O2 (21) One of the striking features of Figure C.6a is the dominant role played by NO2 (reaction (18)), a feature

181 501 45: / .~ 20 ---'I 1 1\1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 \ 1 \! 1\\ ~\ ' ~ ,,HO2+O3 HO?+CtO: \H+O3 ~ 1~<O+OH \ ~ 40 _ - LLJ 35 _ HI 30 ~A\\ in/ / I /' / / ~ At 15 Ally 1 1 1 1 1 1 1111 1 1 1 1 11111 1 1 1 1 1111 o2 103 104 105 1o6 107 RATE (cm~3 sec~l) 103 10° a FIGURE C.6 (a) Rates for production and loss of odd oxygen, averaged over a 24- hour period. The model is the same used in Figure C.1. (b) and (c) Rates for produc- tion and loss of odd oxygen calculated using rate constant sets from Hudson and Reed (1979) and Hudson et al. (1982~. Observed ozone profiles were used in these calcu- lations.

182 40 35 - 30 _ _ Cal 25 cl: 20 16 l 45 40 _ 35 _` - llJ Cal 30 J A: 25 _ 20 \\ i\. , , 30°N Sept. /'/ (OBSERVED OZONE) h As, \. \ \ \ 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 ) .// ~ -a 106 N\;-. 1-. / / .\.1 1981// 2 {0+ clo},~497~<, ///19) / 2 {0 + NO2 } a. 1981 '.:---- C ,,,,, 1 , 1 1 1 1 1 1 ,1 , , , 1 1 1 1 03 104 105 1o6 REACTION RATE (cm~3 sec~1 ) 1 FIGURE C.6 (Continued)

183 that also characterized the earliest studies of strato- spheric NOk and C1X (Wofsy and McElroy 1974, Crutzen 1974, Stolarski and Cicerone 1974, Rowland and Molina 1975). Chlorine radicals influence ozone primarily at altitudes well above the ozone maximum, whereas odd nitrogen radicals are important throughout the stratosphere. Loss profiles for odd oxygen obtained with the best rate data of 1979 (Hudson and Reed 1979) were signifi- cantly different from those shown in Figure C.6a, as may be seen in Figures C.6b and C.6c (see also Table C.1). The 1979 rates imply a major role for reactions of HO2 between 16 and 25 km, and reduced contributions from reactions of NO2. Ozone loss rates may exceed produc- tion rates below 25 km in this model. The principal cycles for HO2 and OH at these altitudes are OH + O3 + HO2 + O2 HO2 + NO ~ OH + NO2 HO2 + O3 ~ OH + 2O2. The sum of reactions (22) and (24) is O3 + O3 ~ 3O2 (net). The sequence (22) and (23) corresponds to little or no net destruction of odd oxygen, since most of the NO2 formed in (23) will be rapidly cycled back to O by (3), and ozone will be regenerated via O + O2 + M ~ O2 + M. The rate at which HO2 catalyzes recombination of ozone (reaction (25)) is very sensitive to [OH]. This rate is given by the production rate for HO2 via (22) multiplied by the fraction of HO2 molecules that react with O3, or net rate for cycle (25) (22) (23) (24) (25) (26) 2k24tH°24[°3] 2k22tOH][°3] 1 + k23[NO]/k24[03] 2k22k24klk4toH] t03] ~ ~(28) 1 k23J2J3[HN°3] (27)

184 Here we have incorporated equation (5b), introducing additional dependence on [OH], and we have exploited the fact that k23[NO] > k24[O3]. In harmony with equation (28), the rate for (24) is reduced using new rate data by about a factor of lo at 20 km, corresponding to the factor of ~3 reduction for [OH] shown in Figure C.2. The present model indicates approximate balance between ozone production and loss at 30° latitude, with production slightly exceeding loss below 25 km. The excess of ozone production over loss is somewhat greater at low latitudes and may reverse sign at high latitudes. Catalytic recombination of two O3 molecules, reaction (25), can potentially exert a major influence on the lower stratosphere, where low concentrations of O limit the rates for (18) and (20). The possible effect of (25) on stratospheric composition remains something of a puzzle, as it has since 1974, in part because transport and chemistry act on comparable time scales in the key altitude range of 20 to 25 km. As discussed below, a dominant role for (25) 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. The isopleths of long-lived radioiso- topes (List and Telegadas 1969, Johnston et al. 1976), fine particles from volcanic eruptions (Lazrus and Gandrud 1974), and gases such as SF6 (Krey et al. 1977), Kr85 (Telegadas and Ferber 1975), and N2O (Golden et al. 1980) exhibit such distributions. Figure C.7a shows the mean contours for these surfaces as deduced from data on Sr90 and C14O2 (see McElroy et al. 1976, Wofsy 1978, and Logan et al. 1978 for details) The isopleths move downward by about 5 km from the tropics to 30°N, fall an additional 3 to 4 km from 30° to 45°N, and move lower by about 1 km from 45°N to the subarctic. Suitable tracer data are available only below 30 km, with most observations below about 22 km. Figure C.7b shows that observed ozone concentrations follow the preferred mixing surfaces at low altitudes and at high latitudes, but at high altitudes the data depart substantially from the isopleths of long-lived tracers.

185 50~1 1 1 1 1 1 1 1 1 1 1 ~ 40 . 30 20 10 _ O 1 ~I 1 1 1 1 1 1 -90 ~30 0 30 LATITUDE 40 30 L`J cat ~ 20 <[ 10 O I I I I I 1 1 1 1 1 1 1 -90 -60 -30 0 30 60 90 SPRING FALL LATITUDE - Transport region TC ~ lmo - Transi t ion zone --- Photochemical cone rc ~ lyr - Ozone replen i shment time _ _ ~ mA . . a A fsurfaces lL} z O 60 90 As I,] Z x 0 _ _ As a 0 0 lmo -4mo lyr -l Oyr 2 1 l 25 km l ~ , (~Okm lo km \ `~25km - 1I5kml 12'km I I ~ 0 30 60 90 LATIT U DE FIGURE C.7 (a) Latitude/altitude cross-section showing orientation of preferred mix- ing surfaces, deduced from data on the distribution of radioactive debris (List and Tele- gadas 1969, Wofsy 1978, Logan et al. 1978~. Contours for ozone replenishment time are also shown. 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 lati- tudes. (b) Isopleths of ozone mixing ratio (ppmv) as functions of latitude. The data are taken from Johnston et al. (1976) for equinoctal conditions. Contours in the photo- chemical zone are represented as broken curves, in the transition zone as thin solid curves, and in the dynamically controlled zone as heavy solid curves. Contours of ozone replenishment time are shown as dotted curves for reference. Ozone follows the pre- ferred mixing surfaces in the transport-controlled region, but departs from these surfaces in the photochemical region. (c) The ozone mixing ratio along several mixing surfaces as a function of latitude. Concentrations of ozone decrease along the mixing surfaces from the low-latitude source region to higher latitudes. Altitudes are indicated along each mixing surface at various latitudes.

186 Closed contours appear near 32 km, a feature that could not be produced without the influence of chemistry. The figure also shows contours for the ozone replenishment time, defined as or = [O3]/2Jo2[O2]' where JO2 is the 24-hour mean photolysis rate for molecular oxygen. It is important to note that the production rate for odd O (2JO2[o2]) is calculated from quantities that have been measured repeatedly and that are unlikely to be substantially in error for the altitude range of interest (<25 km). 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. At these altitudes the time constant for photo- chemical production of ozone (fir) is longer than the turnover time of the lower stratosphere (about 1 year) Where or is shorter than the mixing time along the preferred surfaces, ozone is controlled almost completely by photochemical production and loss. Values for mixing times along preferred surfaces have been estimated to be 1 to 3 months from observations of the spreading rate for radioactive debris (List and Telegadas 1969). Hence above the contour or = 1 month we may assume that, on average, the distribution of ozone is controlled by photochemistry and transport processes are unimportant. The transition zone between regions of photochemical dominance (or < 1 month) and transport dominance (fir > 1 year) extends from 20 to 26 km at 30°N. About one third of the total ozone column lies in the (29) . transition zone. The zone is more extensive at low latitudes, whereas most of the ozone at high latitudes lies in the region of transport dominance. The large concentrations of ozone observed at high latitudes are supplied by production at lower latitudes. If one follows the preferred mixing surfaces from high to low latitudes, they connect to the transition zone we have defined, where rates of transport and chemical production are similar. We anticipate therefore that ozone should exhibit a gradient along the preferred mixing surfaces in the transition zone, with highest concentrations at low latitudes. Figure C.7c confirms this result. We further expect that photochemical production of O3 should exceed loss in the low-latitude

187 source region (20 to 26 km), in order to supply the ozone that moves down this gradient. If we accept as reasonably accurate the O. NO2, and C1O concentrations predicted by the present model, as shown in Figures C.3c, C.3d, and C.5, we cannot accept large rates for catalytic recombina- tion of O3 with O3. We would otherwise calculate a net sink for O3 where there should be a source. This result would appear to apply unless there exists an unknown process capable of dissociating the O2 molecule. we conclude therefore that the set of kinetic rates used in 1979 predicted excessive rates for reaction (24), which were partially offset by an underestimate for the concentration of NO2. We may summarize the argument above as follows. The bulk of the world's ozone is stored at high latitudes, where it is essentially inert. This ozone appears to be supplied by transport along slant mixing surfaces from altitudes between 20 and 25 km at latitudes between 0° and 30°. If substantial recombination of O3 with O3 (reaction (25)) were occurring at these altitudes, chemical loss would significantly exceed production and it would be impossible to provide the source of high- latitude ozone. We argue that (2S) cannot play a dominant role in the middle and low stratosphere. 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 chloro- fluoromethanes (CFMs, Figure C.8a) and nitrous oxide (Figure C.8b). The calculations for CFMs compare model results for the present-day atmosphere (total chlorine 2.3 ppb) with a perturbed atmosphere containing 11.6 ppb of chlorine. The perturbed case corresponds to steady state conditions with constant release of CFMs at rates prevailing in 1977. Increased chlorine markedly reduces ozone above 26 km, with a small ozone increase predicted below that level. The distribution of ozone change reflects the height dependence of the rate for reaction of O with C1O (reaction (20), see Figure C.6a). Since most of the ozone change occurs where photochemistry is dominant, these results do not depend strongly on simulation of transport in the model.

188 60 50 lo 1 1 ' 1 ' 1 ' 1 ' 1 ' !/ _ [Ct X]o~ 2.3 Ppb / ~CIX=9.3ppb J / W ~ -8 -7 - 6-5 -4 ~3 -2 -10 1 '\0( 1011 Cm~3) 2 -60~50 ~40 ~30 -20 -10 0 10 ~O3 (%) FIGURE C.8 (a) and (b) Perturbations to the concentration of ozone as a function of altitude for added C1X and N2 O. calculated using the Harvard one-dimensional model. Results are shown for (a) the change in C1X resulting from constant release of CF2 C12 and CFC13 at 1977 release rates and (b) for a doubling of the N2 0 mixing ratio (Hudson et al. 1982~. The absolute change in O3 is shown in the left-hand panel, and the percent change in O3 in the, right-hand panel. Rate constant sets, 1979 and 1981, are described in Table C.1. (c) History of model calculations since 1975 for the deple- tion of total ozone resulting from constant emission of CF2 C12 and CFC13 (after Hudson et al. 1982~.

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 ~ ~ ~ ~ : ~) 1 -30 -20 -10 ~O3 (1 ol I cm 3) 18 16 L1J o o hi 14 8 8 z 6 llJ ~ 4 o/ ~0 1 1 1 1 1 _ , _ . _ 12 _ . 2 _ C o 1 1 1975 , 76 77 78 79 1980 81 82 YEAR FIGURE C.8 (Continued)

190 The dashed line in Figure C.8a shows the same Clx- perturbation modeled using 1979 rates. The results ar e close to the 1981 model in the photochemical region but are substantially different in the transition zone, 20 to 26 km. 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. Reduced levels of NO and HNO3 amplify the rate for reaction (24) by increasing [HO2] and by decreasing the ratio [NO] / [O3 ], as discussed above. These effects more than offset reduction of the rate of (18), since (24) becomes the dominant loss process for O3 in this model. The contrasting response of O3 in the 1981 model reflects in part the diminished role for (24) obtained with present kinetic rates. There is considerable interest in the response of O3 to increased levels of atmospheric N2O. Nitrous oxide is released to the atmosphere by microbiological processes (vitrification, denitrification) and by combustion, and it is removed in the stratosphere by photolysis, N2O + he ~ N2 + O(1D). (30 ) Approximately 3 percent of the global flux of N2O is converted into NO by the reaction N2O + O(1D) + NO + NO. (31) Reaction (31) is a major source for stratospheric NOX. It has been proposed that agricultural activities (McElroy 1976, 1980) and fossil fuel combustion (Weiss and Craig 1976, Pierotti and Rasmussen 1976) may lead to increased levels of atmospheric N2O, and consequently to higher concentrations of NOX in the stratosphere. Recent observations confirm that N2O is increasing with time (Weiss 1981). Figure C.8b shows the ozone change calculated for a doubling of the N2O concentration, corresponding approximately to a doubling of NOX throughout the stratosphere. Ozone is reduced uniformly by about 15 percent in response to doubled NOX, reflecting the dominant role of (18) in catalyzing recombination of O with O3 (see Figures C.6a and C.6c). It is interesting to note that this calculation is also relatively insensi

191 tive to details of the model example, suppose we treatment of transport. For arbitrarily assume that transport is much faster than chemistry below 26 km, while chemistry is dominant above. The concentration below 26 km would be determined in this case primarily by the O3 concen- tration at 26 km, which is reduced by 15 percent in the perturbation model. If we make the opposite assumption, that chemistry dominates from 26 to 20 km, the calculated ozone reduction is also about 15 percent. However, results for N2O perturbations are likely to be quite different in two- or three-dimensional models, as compared to a one-dimensional model, since significant chemical changes occur in the transition zone that supplies ozone to high latitudes. The calculations using 1981 rates indicate a much larger change for total ozone in response to increased NO AN Smeared to 1979 models. This result applies to NOk introduced by enhanced N2O, by high-flying aircraft, or by any other mechanism. The sensitivity to additional chlorine is reduced from 1979 models by about a factor of 2. 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 environ- mental change. Figure C.8c reviews the history of calculated ozone depletion for continuous release of CFM at rates prevailing in 1977 (after Hudson et al. 1982). Each step on the curve corresponds to new kinetic information. The high values obtained between 1977 and 1978 reflect in part the influence of slow processes that combine O3 with O3. Lower values, near 6 percent, indicate the reduction in column ozone that results from chemical reactions occurring above 25 km. Model results for this region have changed little as new information has become available. Of course, ozone depletion above 25 km could have major indirect effects on the composition of the lower stratosphere, by inducing changes in the dynamics of the stratosphere. Considerable future work is required to define the effect of such coupling between chemistry and dynamics. Present two-dimensional and one-dimensional models give very similar results for ozone reductions due to

192 added chlorine. The global mean decrease in column ozone calculated by Miller et al. (1981) is very close to that predicted by the one-dimensional model (see also Steed et al. 1982). The reduction is nearly uniform over the globe, with variations smaller than +20 percent about the mean. The calculated ozone reduction for a given change in Clx is insensitive to details of the transport, since most of the ozone change occurs high in the atmosphere. Thus the results of Miller et al. (1981) are consistent with the one-dimensional models discussed above. The global mean ozone reduction due to increased N2O is also very similar for one- and two-dimensional models (M. Ko et al., Atmospheric and Environmental Research Inc., personal communication, 1981). In this case, however, the meridional distribution of ozone depletion is not uniform, increasing from about 5 percent near the equator to about 25 percent in the subarctic. Poleward of 45° latitude ozone is strongly affected by increased NOk between 15 and 30 km. As may be seen from Figure C.7b, the upper part of this region lies in the transition zone between the region of control by photochemistry and control by transport. The lower part of the affected region is supplied with ozone by transport from low latitudes. Thus ozone reductions predicted at high latitudes reflect slow consumption by reaction (18) 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. OUTSTANDING PROBLEMS OF PRESENT MODELS FOR THE STRATOSPHERE We attempt in this section to identify important discrepancies between present models and observations of stratospheric composition. These problem areas merit attention in future theoretical and experimental work. Long-lived Trace Gases We examine here results from the one-dimensional model discussed above and from the two-dimensional models of Miller et al. (1981) and Sze and Ko (1981). Miller et al. (1981) use a diabetic circulation (Murgatroyd and J

193 Singleton 1961, Dopplick 1972) to provide the field of mean motions, and they use Hunten's (1975) vertical diffusion coefficient. Horizontal diffusion coefficients are taken from Luther (1974). Sze and Ko (1981) use Luther's coefficients and a consistent set of winds derived from the dynamical study of Harwood and Pyle (1980). Transport in the model of Miller et al. (1981) is adjusted to reproduce the vertical distributions of N2O and CH4 at 30°-40°N latitude, as is the vertical diffusion coefficient used in the one-dimensional model (Logan et al. 1978). Comparison between one-dimensional and two-dimensional models is accomplished using the slant mixing surfaces to project the one-dimensional concentration profile to various latitudes (Wofsy 1978), with the one-dimensional profile taken to represent 30° latitude. This approach is equivalent to a two- dimensional model with infinite mixing rates (perfec t mixing) along the surfaces of preferred mixing. Figure C.9 shows removal lifetimes for CH4, N2O, CF2C12, CH3C1, and CFC13 as functions of altitude for 30°N at equinox. These gases originate in the troposphere and, with the possible exception of N2O (Zipf and Prasad 1980), have no known sources in the stratosphere. Their chemical lifetimes decrease with altitude, reaching one year at 37, 33, 32, 29, and 26 km, respectively. The lifetime for CFC13 approaches meridional transport times near 26 km in the tropics. Two-dimensional models produce meridional distributions of longer-lived gases very similar to those derived from the one-dimensional model, as illustrated for CF2C12 in Figure C.10. This result is hardly surprising, since Luther's diffusion coefficients are based in part on observed contours of potential temperature that are close to the isopleths observed for radioisotopes. 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. Agreement is excellent for the longest- lived species, CH4 and N2O, reflecting in part adjustment of model parameters to fit these profiles. The models significantly underestimate the meridional gradient for CF2C12 and CFC13, but they simulate reasonably well the observed distribution of CH3C1. The results are particularly disappointing for CFC13. Both the vertical and the meridional gradients are

194 50 ~0 - By - 530 At: 20 1 I ~ ~ I I I "1 ' 1\, \ 1 1 ~ ~ , I ,, m1 , , , , , ,,l \\ :_~` I I 1 11 Ill l l ,,,,11 l l ,, 11111 1 1 1,, ,,,, . 10 100 1000 1t LIFETIME (dOYs) FIGURE C.9 Lifetimes of long-lived gases as a function of altitude. Results are appro- priate for 30°N latitude at equinox and are from the Harvard one-dimensional model. Results are shown also for CFCl3 in the tropics. 40 35 30 20 - _ 5 _ 0 _ . 5 l l l till ~ X1012 - 1 D Model with mixing surfaces - Sze et al. Mi Her et al. , , ,,, , , , ,,,, ~ 1 , , 45°( ~ ~ ~ <~> m.1 ,~ ~ 11 lo lo CF2 Ct2 (mole fraction) FIGURE C.lO Calculated profiles CF2 C12 at 0°, 30°, and 45°N latitude.

195 \ 40 30 - - Cl 20 -\ , _ . 10 Oo 0.5 CH4 MIXING RATIO ( ppm) a Ehhalt 44°; 48°N 28/6/79 X15/11/77 16/6/79 +15/12/77 ° 21/12/77 \30°N \\ \~ ~ 45°: .; .~1 \~\ \ Bush et al 41°N 2/14/78 0 5/11/18 Farmer et al 2/76 32°N ~1 Shhalt et al. 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) CH4, (b) N2 O. (c) CF2 C12, (d) CFC13, (e) CH3 C1, and (f) C2 H6 compared with observations. The measurements are discussed in Hudson et al. (1982), and model profiles are from the Harvard one-dimensional model with mixing surfaces, unless otherwise indicated.

196 40 35 30 Y 2 lo c 401 35 30 25 . LIJ => 20 <a 15 0 5 20 C _ _t 10 -12 30°4 0°N~ 45°{~ o '\~ -~SoW~\~ o o i. 5 - I-D With mixing surfaces I ---Sze et al. oL 5_ 10 1 O NOaa 4~1°N ~ K FA 44° N b 1 1 ! 1 1 1 1 1 1 100 N2O ( ppb) 1 1 1 1 1 1 1 1 \ , I I I I 1 1 1 30°N\ 0°N\ O o \ \ A ~45°N~\>,~,~ 0 0 1 1 1 1 1 1 1 1 1 1 'I 1 1 1 1 1 ~o°~ - ^Oo~.. - 1 year chemica I lifetime 1000 ~ . .! ~1 ~ o NOAA 41° N KFA 44°N_ · NOAA 5°N ~.1 . . . . . . . . ~11 lo-lo CF2 Ct2 (mole fraction) FIGllRE C.11 (Continued) lyre Tc it 9

197 40 35 30 25 20 15 10 d _ 10 -12 40 30 r 11~ 25 -- 20 ct 35 15 10 0 0 ° o 5 lo-12 --r ~ I t- I I I I I ~l I ~ /\ 0 \ ~ 6/78 44°N ° 6/28/79 0 6/16/79 1 1 1 1 1 1 1 10-11 \45°N\30°N V ~ ^\ \ o o \ _ ~ I ~ I I I I ~ ~ I I I I I d~ \ lo-lo CFCt3 MOLE FRACTION \ \~\ ~lyr 10-9 1 1 1 1 1 1 1 1 0 NOAA 41° · 5° ~ K FA 44° · ARC, 5° 0 W~ o~o !,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) lmo. 3 most lyr. (30°N) lyr. (0°N) chemicol lifetime 109

198 35 30 _ 25 - lJJ 20 =) ~ 15 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 ~ ~ 1 1 1 1 1 1 1 1 1 . 10 is f - . - - 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) 10 9 10-8

199 incorrect, even in the lower stratosphere. The results in Figures C.10 and C.ll indicate that the two-dimensional and one-dimensional models agree better with one another than with the measurements of CFC13 and CF2C12. 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. This matter is of con- siderable interest, and the difficulty cannot be blamed on the restrictive nature of one-dimensional models. Chemistry at High Latitudes There is a growing body of evidence that concentrations of NO and NOk are sharply reduced at high latitudes in winter (Noxon 1975, 1979, Coffey et al. 1981), although detailed concentration profiles are not available. Present chemical models (both one-dimensional and two-dimensional) predict column abundances of NO and NOk that are 3 to 5 times as large as those observed above 45° latitude. Hence in present models ozone is slowly consumed below 30 km during the period when it should be building up to the spring maximum. Simulations carried out by M. Ko and N.D. Sze (Atmospheric and · . . F.nv i ronmental Research, Inc., personal communication, 1981) confirm that this slow chemistry suppresses the spring maximum in ozone at least for their model. The influence is significant even at midlatitudes and extends into early summer. The discrepancy implies a major defect in our understanding of the chemistry of NOx species. Detailed in situ measurements at high latitudes are mar ; ~ ~" are hm ',n~ - rotund the chemistry of this 1 1 ~ a_ ~ ~ ~ ~ ~ 1~ _ _ ~ ~ ~ ~ at low temperature. one area of weakly bound species like important region. Data on C10, NO, NO2, and HNO3 would be especially revealing. Laboratory measurements are needed to better define the chemistry of NOk species - of interest is the stability ClNO3 and HNO4, which may become major species at cold temperatures and low levels of light (cf. Prather et al. '979, Fox et al. 1982).

200 Chemistry of Key Radicals Atmospheric observations cannot now provide a definitive test for current modelse Measurements of key species such as OH and O are lacking below 30 km, and few sets of simultaneous measurements exist for reactive species in the important families OK, HOk, NOk, and C1X. There are some hints that major discrepancies may emerge as better data are obtained. The difference between observed and calculated C1O at 40 km is particu- larly troubling, since the discrepancy lies near the peak for catalysis by reaction (20). The distribution of ethane departs from the pattern exhibited by other atmospheric halocarbons and hydro- carbons, in that models predict significantly lower concentrations than observed in the middle stratosphere (see Figure C.ll). Since reaction with C1 atoms is a major sink for C2H6 in the lower stratosphere, the observations suggest that models may overestimate the concentrations of C1 below 30 km. There are possible discrepancies for several other important species, including NO (see Figure C.3). SUMMARY STATEMENT Present models predict lower concentrations of stratospheric OH than models in use during the previous NRC study (NRC 1979). This change reflects new data on rates for reactions between OH, HNO3, and HNO4, which provide important pathways for recombination of odd hydrogen radicals in the lower stratosphere. Reduced estimates for OH concentrations imply sharply lower values for the concentration of C1O and higher values for NO and NO2 below 35 km. Agreement between model results and observations is significantly improved by using new kinetic data, but several potentially important ~ . . . cllscrepancles remain. 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) expected from industrial release of chlorofluorocarbons. Most of the ozone reduction is predicted to occur above 30 km, where transport is relatively unimportant. Hence, with current chemistry, results of chlorine perturbation studies are nearly model-independent.

201 Additions of odd nitrogen to the stratosphere produce relatively large reductions in stratospheric ozone, according to current models. This matter is of some concern since the abundance of atmospheric N2O (the major precursor of NOX) is increasing. Ozone reductions due to NOX are distributed uniformly with altitude, affecting the ozone concentration as low as 20 km. Predictions for these ozone perturbations are quite sensitive to details of the transport mechanisms used in the model. REFERENCES Anderson, J.G., H.J. Grassl, R.E. Shetter, and J.J. Margitan (1980) Stratospheric free chlorine measured by balloon-borne in-situ resonance fluorescence. Journal of Geophysical Research 85:2869-2887. Chapman, S. (1930) A theory of upper atmospheric ozone. Memoirs of the Royal Meteorological Society 3:103-125 Coffey, M.J., W.G. Mankin, and A. Goldman (1981) Simultaneous spectroscopic determination of the latitudinal, seasonal, and diurnal variability of stratospheric N2O, NO, NO2, and HNO3. Journal of Geophysical Research 86:7331-7342. Crutzen, P. (1974) A review of upper atmospheric photo- chemistry. Canadian Journal of Chemistry 52:1569-1581. Dopplick, T.G. (1972) Radiative heating of the global atmosphere. Journal of Atmospheric Sciences 29:1278-1294. . Fox, J.L., S.C. Wofsy, M.B. McElroy, and M.J. Prather (1982) A stratospheric chemical instability. (To be submitted to Journal of Geophysical Research.) Goldan, P.D., W.C. Kuster, D.L. Albritton, and A.L. Schmeltekopf (1980) Stratospheric CFC13, CF2C12 and N2O height profile measurements at several latitudes. Journal of Geophysical Research 8S:413-423. Harwood, R.S. and J.A. Pyle (1980) The dynamical behavior of a two dimensional model of the stratosphere. Quarterly Journal of the Meteorological Society 106:395-420. Horvath, J.J. and C.J. Mason (1978) Nitric oxide mixing ratios near the stratopause measured by a rocket-borne chemiluminescent detector. Geophysical Research Letters 5:1023-1026. Hudson, R.D. and E.I. Reed, eds. (1979) The Stratosphere: Present and Future. NASA Reference Publication 1049.

202 Greenbelt, Md.: National Aeronautics and Space Administration; N80-14641-14648. Springfield, Va.: National Technical Information Service. Hudson, R.D., et al., eds. (1982) The Stratosphere 1981. Theory and Measurements. WHO Global Research and Monitoring Project Report No. 11. Geneva: World Meteorological Organization. (Available from National Aeronautics and Space Administration, Code 963, Greenbelt, Md. 20771.) Hunten, D.M. (1975) Vertical transport in atmospheres. Pages 59-72, Atmospheres of Earth and the Planets, edited by B.M. McCormac. Boston, Mass.: D. Reidel. Johnston, H.S., D. Katterhorn, and G. Whitten (1976) Use of excess carbon 14 data to calibrate models of stratospheric ozone depletion by supersonic transport. Journal of Geophysical Research 81:368-380. Krey, P.W., R.J. Lagomarsino, and L.E. Toonkel (1977) Gaseous halogens in the atmosphere in 1975. Journal of Geophysical Research 82:1753-1766. Lazrus, A.L. and B.W. Gandrud (1974) Stratospheric sulphate aerosols. Journal of Geophysical Research 79:3424-3430. List, R.J. and K. Telegadas (1969) Using radioactive tracers to develop a model of the circulation of the stratosphere. Journal of Atmospheric Sciences 26:1128-1136. Littlejohn, D. and H.S. Johnston (1980) Rate constants for the reaction of hydroxyl radicals and peroxynitric acid. EOS Transactions of the American Geophysical Union 61:966. Logan, J.A., M.J. Prather, S.C. Wofsy, and M.B. McElroy (1978) Atmospheric chemistry: Response to human influence. Philosophical Transactions of the Royal Society 290:187-234. Luther, F.M. (1974) Large Scale Eddy Transport. Lawrence Livermore 2nd Annual Report, DOT-CIAP Program, UCRL-51336-74. Livermore, Calif.: University of California Radiation Laboratory. McConnell, J.C. and W.F.J. Evans (1978) Implications of low stratospheric hydroxyl concentrations for CFM and SST scenario calculations of ozone depletion. EOS Transactions of the American Geophysical Union 59:1078. McElroy, M.B.(1976) Chemical processes in the solar system: A kinetic perspective. Pages 127-211, MTP International Review of Science, Series 2, Volume 9, edited by D.R. Herschbach. London: Butterworths. .

203 McElroy, M.B. (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. Aiken. October 1-13, 1979. U.S. Department of Transportation Report No. FAA-EE-80-20. Washington, D.C.: Federal Aviation Administration. McElroy, M.~., J.W. Elkins, S.C. Wofsy, and Y.L. Yung (1976) Sources and sinks for atmospheric N2O. Reviews of Geophysics and Space Physics 14:143-150. Miller, C., D.L. Filkin, A.J. Owens, J.M. Steed, and J.P. Jesson (1981) A two dimensional model of stratospheric chemistry and transport. Journal of Geophysical Research 86:12,039-12,065. Molina, L.T. and M.J. Molina (1981) W absorption cross sections of HO2NO2 vapor. Journal of Photochemistry 15:97-108. Murgatroyd, R.J. and F. Singleton (1961) Possible meridional circulations in the stratosphere and mesosphere. Quarterly Journal of the Royal Meterological Society 87:125. National Aeronautics and Space Administration (1981) Chemical kinetic and photochemical data for use in stratospheric modelling. Evaluation Number 4, NASA Panel for Data Evaluation, JPL Publication 81-3. Pasadena, Calif.: Jet Propulsion Laboratory. National Research Council (1979) Stratospheric Ozone Depletion by Halocarbons: Chemistry and Transport. Panel on Chemistry and Transport, Committee on Impacts of Stratospheric Change, Assembly of Mathematical and Physical Sciences. Washington, D.C.: National Academy of Sciences. Nelson, H.H., W.J. Marinelli, and H.S. Johnston (1981) The kinetics and product yield of the reaction of OH with HNO3. Chemical Physics Letters 78: 495-499. Noxon, J.F. ( 1975) NO2 in the stratosphere and troposphere measured by ground based absorption spectroscopy. Science 189: 547-549. Noxon, J.F. (1979) Stratospheric NO2. II. Global behavior. Journal of Geophysical Research 84: 5067-5076. Pierotti, D. and R.A. Rasmussen (1976) Combustion as a source of nitrous oxide in the atmosphere. Geophysical Research Letters 3: 265-267. Prather, M.J., M.B. McElroy, S.C. Wofsy, and J.A. Logan (1979) Stratospheric chemistry: Multiple solutions. Geophysical Research Letters 6: 163-164. .

204 Rasmussen, R.A. and M.A.K. Khalil (1981) Atmospheric methane: Trends and seasonal cycles. Journal of Geophysical Research 86:9826-9832. Ridley, B.A. and D.R. Hastie (1981) Stratospheric odd-nitrogen: NO measurements at 51°N in summer. Journal of Geophysical Research 86:3162-3166. Ridley, B.A. and H.I. Schiff (1981) Stratospheric odd nitrogen: Nitric oxide measurements at 32°N in autumn. Journal of Geophysical Research 86:3167-3172. Rowland, F.S. and M.J. Molina (1975) Chlorofluoromethane in the environment. Reviews of Geophysics and Space Physics 13:1-3S. Steed, J.M., A.J. Owens, C. Miller, D.L. Filkin, and J.P. Jesson (1982) Two dimensional modelling of potential ozone perturbations by chlorofluorocarbons. Nature 295:308-311. Stolarski, R.S. and R.J. Cicerone (1974) Stratospheric chlorine: Possible sink for ozone. Canadian Journal of Chemistry 52:1610-1615. Sze, N.D. and M.K.W. Ko (1981) The effects of the rate or OH and HNO3 and HONO2 photolysis on the stratospheric chemistry. Atmospheric Environment 15:1301. Telegadas, K. and G.J. Ferber (1975) Atmospheric concentrations and inventory of Krypton-85 in 1973. Science 190:882-883. Turco, R.P., R.C. Whitten, O.B. Toon, E.C.Y. Inn, and P. Hamill (1981) Stratospheric hydroxyl radical concentrations: New limitations suggested by observations of gaseous and particulate sulfur. Journal of Geophysical Research 86:1129-1140. Weinstock, E.M., M.J. Phillips, and J.G. Anderson (1981) In-situ observations of C1O in the stratosphere: A review of recent results. Journal of Geophysical Research 86:7273-7278. Weiss, R.F. (1981) The temporal and spatial distribution of tropospheric nitrous oxide. Journal of Geophysical Research 86:7185-7196. Weiss, R.F. and H. Craig (1976) Production of atmospheric nitrous oxide by combustion. Geophysical Research Letters 3:751-753. Wine, P.H., A.R. Ravishankara, N.M. Kreutter, R.C. Shah, J.M. Nicovich, and R.L. Thompson (1981) Rate of reaction of OH with HNO3. Journal of Geophysical Research 86:1105-1112.

205 Wofsy, S.C. (1978) Temporal and latitudinal variations of stratospheric trace gases: A critical comparison between theory and experiment. Journal of Geophysical Research 83:364-378. Wofsy, S.C. and M.B. McElroy (1974) HOk, NOk and ClOX: Their role in atmospheric photochemistry. Canadian Journal of Chemistry 52:1582-1591. Zipf, E.C. and S.S. Prasad (1980) Production of nitrous oxide in the auroral D and E regions. Nature 287:525-526.

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