Jan 20, 1996 - Heterogeneous atmospheric bromine chemistry. D. J. Lary and M. P. Chipperfield. Centre for Atmospheric Science, Cambridge University, ...
JOURNALOF GEOPHYSICALRESEARCH,VOL. 101,NO. D1, PAGES1489-1504, JANUARY20, 1996
Heterogeneous atmospheric bromine chemistry D. J. Lary and M. P. Chipperfield Centrefor AtmosphericScience,CambridgeUniversity,Cambridge,England R. Toumi
Department,of Physics,Imperial College,London, England T. Len•on
Centre for AtmosphericScience,CambridgeUniversity,Cambridge,England
Abstract.
This paper considersthe effect of heterogeneous brominereactionson
stratospheric photochemistry. We have consideredreactions on both sulfate aerosols
andonpolar stratospheric clouds(PSCs). It is shownthat the hydrolysisof BrONO2 on sulfate aerosolsenhancesthe HOBr concentration,which in turn enhancesthe OH and HO2 concentrations,thereby reducingthe HC1 lifetime and concentration.
The hydrolysis of BrONO2leadsto a nighttimeproductionof HOBr, makingHOBr a major nighttimebrominereservoir.The photolysisof HOBr givesa rapid increase in the OH and HO2 concentrationat dawn, as was recentlyobservedby $alawitch et al. [1994].The increasein the OH and HO2 concentration, and the decrease in the HC1 concentration,leadsto additional ozonedepletionat all latitudes and for all season.At temperaturesbelow210 K the bulk phasereactionof HOBr with HC1 in sulfateaerosols becomes important.The mostimportantheterogeneous bromine reactionson polar stratosphericcloudsare the mixedhalogenreactionsof HC1with HOBr and BrONO2 and of HBr with HOC1 and C1ONO2.
Introduction
phase chemistry, fortherapidconversion ofHC1into C1Ox(=Cl+C10+2C1202). Sincethe timescalefor HC1
TherecentWorldMeteorological Organization (WMO) productionis severaldaysit is only recycledslowly. assessment [1992]reportedthat for the first time there Therefore,the heterogeneous reactionsconsiderably perare statistically significantdecreasesin ozonein all sea- turb the chlorine partitioning. In contrast, because sonsin both the northern and southernhemispheres at bromine speciesare short-livedheterogeneous bromine middle and high latitudes during the 1980sand that reactions are important as they allow the formation of most of this decreaseis occurringin the lower strato- catalytic cycles for the conversionof H20 into HOx
sphere.This findinghas alsobeensupportedby trends (=OH+HO2), HC1 into C10 and NOx (=NO+NO2) derivedfrom ozonesondes [Logan,1994]. This paper into HNO3, as well as for the rapid recyclingof the showsthat at leastpart of this ozonelossis likely to be brominereservoirspeciesBrONO2 and HBr. This leads dueto in situ heterogeneous brominereactions. to ozonelossat all latitudesand for all seasons, particThe atmospheric chemistryofreactivebrominespeciesu!arly whenhighloadingsof sulfateaerosolare present
is characterized by their shortlifetimes.The longest- in the atmosphere. lived reactive bromine speciesis HBr, which has a lifetime of up to a day but constitutesonly a smallfraction Calculation of Heterogeneous Reaction
of the total reactivebromine(BrOy) presentin the at- Rates mosphere [Lary,1995]. In contrast,the longest-lived
Table 1 showsthe heterogeneousbromine reactions reactive chlorinespeciesis HC! which typically has a lifetime of over a weekin the lowerstratosphereand of- used in this study. This set of reactions was constructed chlorinereten constitutesthe largest fraction of the total reactive by analogywith the known heterogeneous
chlorine(ClOy) presentin the atmosphere.
•aions. a•c•ly,
,'•ction• (1) •nd (2)in T•bl• • h•v•
Papernumber95JD02839. 0148-0227/96/95JD-0283 9505.00
as bulk phase reactions on sulfate aerosolsbecause of
"7 Heterogeneous chlorinereactionsare important be- beenstudiedby Abbatt[1994]on ice. The measured causethey providea mechanism,not providedby gas valuesare very similar to the value of 0.3 for the reaction HOC1with HC1onwaterice[HansonandRavishankara, Copyright 1996bytheAmerican Geophysical Union. 1991;Abbattand Molina, 1992]. Reactions(1) to (3)in Table 1 have been treated 1489
1490 Table
LARY ET AL.: HETEROGENEOUS 1.
ATMOSPHERIC
CHEMISTRY
AH as K
Surface
kJ/Mole
Type
A
A,I,II A,I,II A,I,II I,II I,II I,II A,I,II I,II
B B B
HeterogeneousBromine ReactionsUsed in This Study
Reaction
(R1) (R2) (R3) (R4) (R5) (R6) (R7) (R8)
BROMINE
* *
* * *
HBr HC1 HBr HBr HC1 HBr H•.O HBr
4+ 4+ + + 4+
HOBr ) HOBr ) HOC1 ) BrONO•. > BrONO• > C1ONO•. ) BrONO•. • N•.O5 --4
Br•. BrC1 BrC1 Br2' BrC1 BrC1 HOBr BrONO
4+ 4+ + + 4+
H•.O H•.O H20 HNO3 HNO3 HNO• HNOa HNOa
-95.3 -55.6 -115.8 -118.2 -78.5 -107.3 -22.9 -5.6
7 I
II
0.1 0.1 0.1 0.3 0.3 0.3 0.45 0.006 0.005õ
0.12• 0.25t 0.3 0.3 0.3 0.3 0.3 0.005õ
The assumed radiiusedin thisstudyfor sulfateaerosol (A), PSCI (I) andPSCII (II) are0.1pro,0.1pro,10pm
respectively.B, a bulk phasereaction. ,, a key reaction.
õFromHansonandRavishankara [1992]. tFromAbbatt[1994]. *FromHansonandRavishankara [1995].
their diffusoreactivelength. For example, as mentioned
Heterogeneous Bromine Catalytic
by Danilin and McConnell[1995],the diffusoreactive Cycles lengthof reaction(2) exceedsi pm for 60 wt % H2SO4 solution. The rates of the bulk phase reactions are calThe hydrolysisof BrONO2 is the rate-limitingstep culated as a function of temperature by usinga Henry's law coefficient and an aqueous phase bimolecular rate
coefficientas describedby Cox et al. [1994].The bulk phasereactions are fastest at cold temperaturesand for high water concentrationsand are therefore most important in the region closeto the tropopauseor whet'ever the temperature falls below 210 K.
of a catalytic cyclein which H20 is split and converted into HO2. Three ozonemoleculesare destroyedfor each moleculeof BrONO2 hydrolyzed. Cycle A
+ + +
H20 hv 03
HOBr
+
hv
a function of temperature and effectivehydrogencon-
OH Br
+ +
03 03
centrationin the mannerdescribed by Coxet al. [1994].
BrO
+ NO2 M> BrONO2
In each case the bimolecular
rate coefficient
for the
liquid phasereactionis taken to be 105M -• s-•. The effective Henry's law coefficient for HC1 is calculated as
The effective Henry's law coefficient for HBr is calcu-
BrONO2 HNO3 OH
> HOBr > OH > HO2 >
OH
' > HO2 > BrO
+ + +
HNO3 NO2 02
+
Br
q+
02 02
+ 303 > 2H02 + 302 lated after DeMoreet al. [1994](seealsoBrimblecombe H20 and Clegg[1988]).The effectiveHenry'slaw coefficient CycleA is represented schematically in Figure1. for HOBr is takento be 10ø M/arm in accordance with Cycle A has a long chain length for enhanced levels the resultsof HansonandRavishankara [1995]at 210 K. of sulfate aerosol reaching a peak of over 10 • between In marked contrast to the hydrolysis of C1ONO2 on sulfate aerosols, the hydrolysis of BrONO2 on sulfate
aerosols(reaction(7) in Table 1)is not a strongfunc-
I
Conversionof H20 into OH
tion of temperature[HansonandRavishankara, 1995] (seeFigure3 later). Hansonand Ravishankara [•9921 studied the heterogeneousreaction of HBr with N205
(reaction(8) in Table 1). Where7 valueswereunavailable, the 7 values used for the bromine reactions were taken to be the same as those of their chlorine ana-
logues. The key heterogeneous bromine reactionsare marked
with a largestar in Table 1. They involvethe relatively abundant bromine speciesHOBr and BrONO2. The
net effectof thesereactionsis to convertBrOy from BrONO2 and HBr into HOBr and BrC1. The HOBr
cansubsequently be photolyzedor heterogeneously con- Figure 1. Reactionschemeshowingthe effectsof into BrC1. BrONO2 hydrolysison sulphateaerosols.
verted
LARY ET AL.: HETEROGENEOUS
ATMOSPHERIC
BROMINE
BrONO2Hydrolysis catalyticcycle 1o'•
10ø
10'
102
10•
CHEMISTRY
1491
HOBr+ HCIcatalyticcycle 104
30
10•
30
30 _
10•
, i •l•l
_
10'
• , illrill
100
10' i
• I J,,,,,I
i iiillll
10• i
i iiiiii
_
_
AerosolLoading
_
_
_
......
_
25--
•,
-25
_
Background
........... Volcanic
25-
_
-25
_
E
_
..•
_
_
_ _
(i) 20•
,
-
•
-
•
_
(i) 2o-
-20
,,,,
_
_
"o •
-
•
-
-20 t
'
_ _
• 15--AerosolLoading ...... Background
J
//
/
,,/
/
lO'
-15
. .....
15-
-15
_ _
......
.....Volcanic _..-_..•:.•.-•-""/'""
lO
_
100
_
lO
lO
o4
10
o3
lO'
10'•
ChainLength
lO0
10'
10•
ChainLength
Figure 2. The chain lengthsof the ozonedestroyingBrONO2 hydrolysisand the HOBr+HC1 catalytic cyclesfor backgroundand volcanic loadingsof sulphate aerosol.
about 15 km and 20 km (Figure 2). The chain length centration can reduce the HC1 lifetime by up to a facis a measure of how many times the cycle is completed tor of 3. The reduced HC1 lifetime, and the accombefore the chain center is removed. Because the chain panying increasein the C10• concentration,alters the length is a ratio of two rates, it is dimensionless. It is C1ONO2/HC1ratio, enhancingthe effectiveness of the
discussed in moredetailin the companion paper[œary, two gasphaseC10/BrO catalyticcycles. this issue]whereit is definedasthe rate of propagation Both the production and destruction of HNOa in(the rate of the rate-limitingstep), kr•sdividedby the volve OH. However, owing to the relative rates of these rate of production or destruction of the source gases. two reactions, the increase in the OH concentration ink dest. creasesthe production of HNOa more than it enhances
chainlength,;V' =
]Crls
]Cdest
the HNOa
(1)
destruction.
As a result the ratio of the
HNOa production timescaleto the HNO• losstimescale increases fi'om between
1.5 and 2 in the lower strato-
sphereto approximately 3 when heterogeneousbromine The rate of the rate-limiting step reaches a peak of reactions on enhanced loadings of sulfate aerosolsare approximately1600molecules cm-3 s-1 closeto 18 km included for noon at mid-latitudes at equinox. This
for enhancedlevels of sulfate aerosol, and approximately
increase in OH leads to an increase in the HNOa con-
150molecules cm-3 s-1 for background levelsof sulfate centration at the expense of the NO2 concentration. aerosol.
At cold temperatures the HOBr formed by BrONO2 The stickingcoefficientfor hydrolysisof BrONO2 on hydrolysis can react with HC1 within sulfate aerosols sulfate aerosolsis not temperature dependent. Cycle A to produce BrC1 instead of being photolyzed. This cycan proceed whenever sunlight is present. It is therecle couplesthe atmosphericchemistryof chlorine and fore important for ozone loss at all latitudes and for all bromine, releasingactive chlorinefrom HC1. Each time seasonsin the lower stratosphere. For example, over the cycle is executed, HC1 is converted into C10 and a 40-day mid-latitude simulation of a vertical profile three ozone molecules are destroyed. in a one-dimensionalmodel at the equinox, including heterogeneousbromine reactions reduced the ozone col- Cycle B
umn by 11.2%for volcanicaerosolloadingsand by 5.4% BrONO2
for background aerosol loadings. The ozone loss due to heterogeneousbromine reactions took place in the troposphereand the lower stratosphere. Although this study did not include the effects of rain out in the troposphere, it is clear that heterogeneousbromine reac-
HNO3 OH HOBr
+ + + +
H20 h• 03 HC1
BrC1
+
Br
tions are alsoimportant in the troposphere[Fan,and C1 Jacob, 1992; Finlayson-Pitts et al., 1990; McConnell et
al., 1992;Toumi,1994].
BrO
) > >
HOBr OH HO2 BrC1
+ + + +
HNO3 NO2 02 H20
h•
>
Br
+
C1
+ q-
03 03
> >
BrO C10
+ q-
02 02
+
NO2 M> BrONO2
--•
+ 303 • HO2 q- C10 q- 302 Cycle A enhancesthe OH concentrationand thereby HC1 indirectly couples the atmospheric chemistry of chloThe rate of the bulk phasereactions(1) to (3)in rine and bromine, because the increase in the OH con- Table 1 are a strong function of both the temperature
1492
LARY ET AL.: HETEROGENEOUS
ATMOSPHERIC
and the water vapor concentration. Therefore cycle B is only effective in the cold temperatures found in the very low stratosphere.For enhancedaerosolloadingsit
has a chainlengthapproaching100 (Figure2). Figure 3 showsthat the hydrolysisof BrONO2 on sulfate aerosolsis effectiveover a wide range of temperatures.
It can be seen that
in absolute
terms
it has a
relatively low rate, underlining the fact that its importance is due to its being part of a catalytic cycle. It is interesting that even though the sticking coefficient is not a function of temperature, the absolute rate of
BrONO2 hydrolysisin units of molecules cm-3 s-• is temperaturedependent(Figure3). This is becausethe BrONO2 concentration is very sensitiveto the amount of NO2 present, which is in turn a function of the tem-
BROMINE
CHEMISTRY
crease in OH and HO2 is in agreement with the recent SPADE observations of OH and HO2 reported
by $alawitchet al. [1994]. The simulationsshownin Figure 4 used the initial conditionsgiven in table i of
$alawitchet al. [1994]and assumed 14 pptv of BrOy. $alawitchet al. [1994]explainedthe suddenincreasein OH and HO2 at sunriseby the heterogeneous conversion of HO2NO2 into HONO. However, Figure 4 showsthat at least part of the sudden sunriseincreasein OH and HO2 is due to BrONO2 hydrolysisenhancingthe HOBr
concentration.Hansonand Ravishankara [1995]mentioned that BrONO2 hydrolysisproducesenoughHOBr during the night to give a releaseof OH at dawn. When using the HOBr crosssectionsof Orlando and
Burkholder[1995]the inclusionof heterogeneous bromine peratureand ozoneconcentration [Lary,1991];Lary et reactions leads to a slightly lower BrO concentration al., 1994]. A similareffectis observedin the rate of for a short period immediately after dawn as HOBr is N205 hydrolysis(Figure3). By comparingthe ratesof photolyzed slightly more slowly than BrONO2. The BrONO2, N205 and C1ONO2 hydrolysisshownin Figure 3 it illustrates that the reduction in NO x and en-
hancementin HNO3 that occurswhen BrONO2 hydrolysis is included is not due to the hydrolysis of BrONO2 alone, a relatively slow process, but is also due to the increasein OH releasedby the photolysisof the HOBr that
is formed.
In agreementwith the findingsof Hanson and Ravis-
decreasein BrO in the short period just after dawn would not occur if HOBr photolysis was faster than BrONO2 photolysis. The bulk phasereaction of HOBr with HC1 proceedsat night causinga slow,but steady,
increaseof BrC1duringthe night (Figure4). At high latitudes in the cold stratosphereunder volcanic conditions the reaction of HOBr with HC1 proceedsat a nmch higher rate, leading to a couplingof bromine and chlo-
(seealsoDanilinandMcConnell[1995]). hankara[1995]it wasfoundthat at temperatures below rinechemistry approximately 210 K the fastest stratosphericheterogeneousbromine reaction is the bulk phasereaction of
HOBr with HC1. At the tropopauscandbelow,the high Partitioning water concentrationsenable the bulk phase reaction of HOBr with HC1 to proceedvery rapidly.
of Reactive Species
The inclusionof heterogeneousbromine reactionsal-
terstheBr/BrO, C1/C10,NO/NO2 andOH/HO2 ratios as well as altering the absoluteconcentrationsof these species. There is an increasein the BrOx, C1Ox and
Diurnal
Cycles
HO• concentrations and a decrease in the NOx con-
centration. The Br/BrO ratio is reducedwhen hetThe hydrolysis of BrONO2 has a marked effect on the shape of the BrONO2 and HOBr diurnal cycles (Fig-
erogeneousbromine reactions are included due to the decrease in the NO concentration, and hence the rate
ure 4). Duringthe dayBrONO2is rapidlyproduced by of the reactionof BrO with NO. The C1/C10 ratio is the three-body reaction of BrO with NO2, and the hydrolysisof BrONO2 is not fast enoughto competewith the photolysis of BrONO2. Therefore at mid-latitudes BrONO2 hydrolysis has a relatively small effect on the daytime BrONO2 concentration. However, after sunset, BrONO2 production ceasesand any BrONO2 presentis converted into HOBr on the timescale of a few hours, so that at the end of the night little BrONO2 remains
if enhancedaerosolloadingsare present(Figure 4). BrONO2 would otherwisebe a major BrOy reservoir
reducedwhen heterogeneousbromine reactionsare included due to the decrease in the NO concentration, and hence the rate of the reaction
of C10 with NO. The
NO/NO2 ratio is reducedwhenheterogeneous bromine reactions are included due to the increase in the C10, BrO, HO2 and CH302 concentrations,and hence, the
rate of their reactionswith NO. The OH/HO2 ratio is reduced when heterogeneousbromine reactions are included due to the decrease in the N O concentration the increase
in the C10
concentration.
This
and
decreases
as the reaction of BrO with NO2 goes to completion. the rate of the reaction of HO2 with NO and increases Consequently,the largest differencein the calculated the rate of the reaction of C10 with OH. Duringperiodsof enhancedaerosolloadingthe HC1/ BrONO2 concentrationdue to heterogeneousbromine
reactionsoccursjust beforedawn(Figure4).
ClOy ratio is reducedowingto the increasein OH by the
The increase in HOBr is due to the hydrolysis of BrONO2 during the night causesa suddenincreasein
catalytic hydrolysisof BrONO2 and a correspondingde-
creasein the HC1lifetimeandconcentration (Figure5).
the OH and HO2 concentrations at dawn as HOBr is
The effect is most pronouncedin the lower stratosphere.
rapidly photolyzed(Figure 4). This suddendawn in-
The decreasein the HC1/C1Oyratio is accompanied
LARY ET AL.: HETEROGENEOUS
ATMOSPHE
,RIC BROMINE
BrONO• + H•O-+ HOBr + HNO• 0
I
2
3
4
CHEMISTRY
1493
HOBr + HCI-+ BrCI + H•O
5
0
240 I , , , , • , , , , I , , ,_, • , , , ;---!--•_-L•_-'•, _-_'....-'_... 240
I
2
I ....
,,
240 I , , ,,
3
.,.
4
5
......
•240
_
230
230
230
230
:::::::::::::::::::::::::::::::
160 ................. •::• ..........
220
.... •i:•ii220
•
::::::::::::::::::::::::::::::
,•,
700"'"'"'"'"'"'"':':•::'•:•:. ............ :•:•
•' 220
220 600,--:.,,,...
80':::%: :,7 210
.210
210 :::::::::::::::::::::::::::::::::::::::::::::::::::::::::: "-''"'-•"-•'"'""••:'"'"•'•"•••:;: 210300',•:'", "•
:::::;::::::::":•'•"...\•':• -.=========:=====:==,===== 200
O0 ..::::.. ................ .: ::::::::::::::::::::::::::::::: -":••••••:::':':'"':•:•:::'•':':::-:-:'-. ....................................... •":-:•• 200 ::::::::::::::"'::•"' :•'"•'"?:4•:: '.' ß:::::
::...::::::::::::::::::::::::::::::::: ................. !::•i:::•::::•:i:•::.q:i•:...`i•`•::i•:`•.!•::•..4•.•?:::.`.•::::•-q!::•i•.``.•.:•..•::•::•: i.......... :.-::::.-..:.•:.s:::..-.:.::::::::..:..]!:i•::5•:5::!:•:ii::::::!•:•:•!•!•i??iii!!i•:::i•:•::..:;•:::::..`.•:..x4•.X:`..:[•.%i::i.`.::[!•!•: :.•....:..::'.-:--I, •.:::..---?-:--': .-.: :.i:i:[Sii•i!i!ii:.:.:.!:...-.:•.x.?.•iiiiiSiiii:;:-Li:::...:..-.'•..-.w-:....-?:•f.(•:?:.-:.!:::i ' .:Y.{:':.'.Y::.!:::::':':.'..-.::?--::!':-!-::'::-'!:
:
Contour from .1 to .8 by .1 (X 1) 0.2
0.3
0.4
0.5
0.6
0.7
0.8
:
Contour from .1 to .8 by .1 (X 1) I
0.1
:
[•i•i•i•i•i•i•½•f•½t'"'"'•:':C12+H20 on ice and nitric-acid
reducingthe HC1 and NOx concentrations.The addi-
tional C1Ox and BrO.• activation that results enhances
103 for enhancedaerosolloadings. The enhancement
in the OH concentration can substantially reduce the
HC1 lifetimeand HC1/C1Oyratio in the lowerstrato-
trihydrate: reaction probabilities and stratosphericimplications, Geophys.Res. Left., 19 (5), 461-464, 1992. Abbatt, J.P. D., Heterogeneousreaction of HOBr with HBr
and HC1 on ice surfaces at 228 K, Geophys. Res. Left., 21 sphere.The nighttime hydrolysisof BrONO2 leadsto a (8), 665-668, 1994. nighttimeenhancementof HOBr, sothat at dawnHOBr Brimblecombe, P., and S.L. Clegg, The solubility and bephotolysisleads to a rapid rise in OH and HO2 as has haviour of Acid gases in the marine aerosol, J. Atmos. recentlybeenobservedby $alawitchet al. [1994]. Chem., 7, 1-17, 1988. For a simulation
of the winter
of 1992-1993
on the
475 K isentropicsurfaceconstrainedby ECMWF analyses, under nonvolcanic conditions the hydrolysis of BrONO2 led to an additional O3 depletion at northern mid-latitudes of up to 18 ppbv during the 2-month model run. With a volcanic aerosol loading the northern mid-latitude ozone depletion increasedto 40 ppbv, while in the summer of the southern hemispheresignificant additional ozone depletion of over 130 ppbv was producedalong with changesto ClO and H02. On PSCs the most important heterogeneousbromine reactions are the mixed halogen reactions of HC1 with HOBr and BrONO2 and HBr with HOC1 and C1ONO2. Acknowledgments. The authors wish to thank J. A. Pyle for his support, R. A. Cox and J. Sesslerfor useful conversations and D. R. Hanson• A. R. Ravishankara, J. J. Orlando, J. B. Burkholder and M. Danilin for making their results available to us before publication. The Centre for Atmospheric Scienceis a joint initiative of the Depart-
Burkholder, J. B., A. R. Ravishankara and S. Solomon, UV visible and IR absorption cross-sectionsof BrONO2, J.
Geophys.Res., 100 (D8), 16,793-16,800, 1995. Chipperfield, M.P., D. Cariolle, P. Simon, R. Ramaroson and D. J. Lary, A three-dimensional modeling study of trace speciesin the Arctic lower stratosphere during winter 1989-1990, J. Geophys. Res., 98, 7199-7218, 1993. Chipperfield, M.P., D. Cariolle, and P. Simon, A 3D chemical transport model study of chlorine activation during EASOE, Geophys. Res. Left., 21, 1467-1470, 1994. Chipperfield, M.P, A 3D Model comparisonof PSC process-
ing during the Arctic winters of 1991/92 and 1992/93, Ann. Geophys., 12, 342-354, 1994. Chipperfield, M.P, J. A. Pyle, C. E. Blom, N. Glatthor, M. H;Spfner, T. Guide, C. Piesch and P. Simon, The variability of C1ONO2 and HNOa in the Arctic polar vortex: Comparison of Transall MIPAS Measurements and 3D Model Results, J. Geophys. Res., 100, 9,115-9,129, 1995.
Cox, R. A., A. R. MacKenzie, R. H. Muller, T. Peter and P. J. Crutzen, Activation of stratospheric chlorine by reac-
tions in liquid sulfuric acid, Geophys.Res. Left., 21 (13), 1,439-1,442, 1994.
1504
LARY ET AL.: HETEROGENEOUS ATMOSPHERIC BROMINE CHEMISTRY
Danilin, M. J., and J. C. McConnell, Stratosphericeffects McConnell, J.C., et al., Photochemicalbromine production of bromine activation on/in sulfate aerosol,J. Geophys. implicated in Arctic boundary-layerozonedepletion,NaRes., 100 (D6), 11,237-11,243,1995. ture, 355 (6356), 150-152,1992. DeMote, W. B., et al., Chemical kinetics and photochemical Mellouki, A., R. K. Talukdar and C. J. Howard, Kinetics of data for use in stratosphericmodeling, Evaluation Numthe reactions of HBr with O3 and HOa: the yield of HBr ber 10, Jet Propul. Lab., Pasedena, Calif., Publ. 9•-26, from HOa + BrO, J. Geophys.Res., 99 (Dll), 22,9491994.
Fan, S.M., and D. J. Jacob, Surfaceozonedepletionin Arctic spring sustainedby bromine reactionson aerosols,Nature, 359, 6395, 522-524, 1992. Hanson, D., and K. Mauersberger,Laboratory studiesof the nitric acid trihydrate: Implications for the south polar stratosphere, Geophys.Res. Left., 15, 855-858, 1988.
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Orlando, J.J., and J. B. Burkholder, Gas phaseUV/visible absorption spectra of HOBr and BraO, J. Phys. Chem., 99 (4), 1,143-1,150,1995. Salawitch, R. J., et al., The diurnal-variation of hydrogen, nitrogen, and chlorine radicals: implications for the heterogeneousproduction of HNO=, Oeophys._Res.Lett., œ1 (23), 2,551-2,554,1904.
Hanson,D.R., and A. R. Ravishankara,Investigationof the reactive and nonreactiveprocesses involvingC1ONO2and Sessler, J., M.P. Chipperfield, J. A. Pyle and R. Toumi, HC1 on water and nitric-acid dopedice, J. Phys. Chem., StratosphericOC10 measurementsas a poor quantitative indicator of chlorine activation, Geophys.Res. Lett., œœ 96 (6), 2682-2691,1991. Hanson, D.R., and A. R. Ravishaukara, Heterogeneous (6), 687-690, 1995. chemistryof HBr and HF, J. Phys. Chem.,96 (23), 9441- Toumi, R., BrO as a sink for dimethylsulfide in the marine 9446, 1992. atmosphere,Geophys.Res. Lett., œ1(2), 117-120, 1994. Hanson, D.R., and A. R. Ravishankara, Heterogeneous WMO, ScientificAssessmentof StratosphericOzone: 1991, chemistry of bromine speciesin sulfuric acid under stratoWMO Global Ozone Research and Monitoring Project, Report œ5,Geneva, Switzerland, 1992. sphericconditions, Geophys.Res. Lett., 2œ(4), 385-388, 1995.
Lary, D.J., Photochemical studies with a 3D model of the atmosphere,PhD. thesis, Cambridge Univ., Cambridge, England, 1991. D. J. Lary, M.P. Chipperfield and T. Lenton, Centre Lary, D.J., Gas Phase Atmospheric Bromine Photochemfor Atmospheric Science,Department of Chemistry, Camistry, J. Geophys.Res., this issue. Lary, D. J., J. A. Pyle and G. Carver, A 3D model study bridge University,Lensfield Road, Cambridge, CB2 1EW, atm.cm.cam.ac.uk) of nitrogen-oxidesin the stratosphere, Q. J. R. Meteorol. U.K. (eraall:david@ Soc., 1œ0(516), 453-482, 1994. R. Toumi, Department of Physics,Imperial College,LonLary, D.J., M.P. Chipperfield and R. Toumi, The potential don, SW7 2BZ, U.K. impact of the reaction OH+C10-•HCI+O2 on polar ozone photochemistry,J. Atmos. Chem., œ1(1), 61-79, 1995. Logan, J.A., Trends in the vertical distribution of ozone: An analysisof ozonesondedata, J. Geophys.Res., 99 (D12), (ReceivedMarch 9, 1995; revisedJune 28, 1995; 22,553-25,585, 1994. acceptedAugust 24, 1995.)
