JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 86, NO. C8, PAGES 7267-7272, AUGUST 20, 1981
Vertical Profilesof Ethaneand Propanein the Stratosphere
J. RUDOLPH, D. H. EHHALT, AND A. TC)NNISSEN
Institutfiir Chemie,
Atmosphdrische
Chemie,Kernforschungsanlage
JiilichGmbH,D-S170Jiilich,FederalRepublicof Germany
Stratospheric
measurements
of the C2H6mixingratio up to 30 km and of the C3Hsmixingratio up to
18km altitudearereported.The observed
verticalgradientof C2H6is muchweakerthanthat calculated
from a one-dimensional
steadystatemodel,indicatinglower concentrations
of atomicchlorinein the
lowerstratosphere
thanthosepredictedby models.From the measuredC2H6profilea tentativeestimate
for the CI concentration
is derived.
INTRODUCTION
Balloon-bornecryogenic
collectionprovidesrelativelylarge
samples(10 1 STP) of uncontaminated
stratospheric
air. This
facilitatesthe simultaneousmeasurementof a largenumberof
tracegasesto high stratospheric
altitudes.We havenow extendedour programto includethe measurement
of light nonmethanehydrocarbons,
C2 to Cs,and we reporthereour first
measurementsof ethane, C2H6, and propane, C3Hs, in the
stratosphere.
ppt for C2H6at 30 km altitudeand 10ppt for C•Hs at 18 km
altitude.The errorsof the gaschromatographic
measurement
are 10%for tropospheric
mixingratios;they.increaseto a fac-
tor 2 for samples
withmixingr•tiosnearthedetection
limit.
RESULTS
The stratosphericdata were obtained from two balloon
•ts
over southernFrance at 44øN on June 16 and 28, 1979.
The troposphericsampleswere collectedduring an aircraft
flight on June 16, 1979.The samplingwaspart of a joint project for the measurementof stratospherictrace gasesby the
KernforschungsanlageJalich, the Max-Planck-Institut for
The tropospheric
backgroundmixing ratiosof both are
quitelow, about2 ppb for C2H6and lessthan ! ppb for C•Hs
[Rudolphet al., 1979].The fluxesof thesegasesinto the stratospherearesmall,and theirimpacton the stratospheric
carbon Aeronomie in Lindau, and the Max-Planck-Institut
for
and hydrogenbudgetis negligible.Nevertheless,C2H6reacts
Chemie in Mainz. In addition to C2H6 and C•Hs the troporapidly with CI atoms,and its presenceshouldsignificantly
spheric samplesalso showed measurableconcentrationsof
decreasethe CI atom concentrationin the lower stratosphere
C2H4, C2H2, n-C4H•o,i-C4H•o, n-CsH•2, and i-C5H•2. Only
[Aikinet al., 1979].Furthermore,alreadythe firstmodelcalcuC2H2,C2H6,and C3Hscould be detectedin stratosphericair
lations [Chameidesand Cicerone,1978]indicatedthat the resamplesabove 15 km altitude.
actionwith C1atomsis by far the dominantlossmechanismof
The C•Hs and C2H6data are summarizedin Figures I and
C2Hsin the stratosphere.
Henceits verticaldistributionshould
2. The measuredC•Hs mixing ratio decreasesextremelyfast
be controlledby the verticaldistributionof the CI concentrawith altitudeabovethe tropopause(11 kin). Above 18 km altition. Consequently,
measuredprofilesof C2H6couldserveas
tude it is alreadybelow the detectionlimit of 10 ppt.
a convenientmethodfor determinationof the vertical profile
The measuredstratosphericC2H6mixing ratios (Figure 2)
of CI atomsin the lower stratosphere,a region where direct
exhibit a similar rapid decreasewith altitude. Becauseof its
observationsof CI are not yet feasible.Here we use our preshighertropospheric
mixingratio, 2 ppb, and a lower detection
ent C2H6profilesto derive an estimatefor the CI concentralimit, 2 ppt, the C.•H6can be observedto about 30 km altitude.
tion in the lower stratosphere.
EXPERIMENTAL
PROCEDURES
The stratospheric
air sampleswere collectedby a balloonbornecryosampler
similarto the designdevelopedby Lueb et
al. [1975].The samplingprocedureshavebeenpresentedelsewhere [Fabian et al., 1979a]. The troposphericair samples
were collectedaboard an aircraft by grab samplingin electropolishedstainlesssteelcontainersof 2-1volume.After return to the laboratorythe air samplesof 1-5 1 STP were analyzed for their hydrocarbon content using a specially
equippedgaschromatograph:
The hydrocarbons
are first enrichedon a precolumnpackedwith Spherosiland Carbosieve
B and cooledto temperatures
of about 150K, then thermally
desorbedand separatedon a column packedwith Spherosil
XOB 075 (6 m long and 0.8 mm inner diameter),and finally
detectedwith a flame ionization detector.The gas chromatographicmeasurements
werecalibratedwith standardmixtures
of 0.5-3 ppb of C2H6and C•Hs in syntheticair, which were
preparedby three-step
dilutionin a staticdilutionsystem.The
detectionlimits dependedon actual samplesize and were 2
Copyright
¸ 1981by the AmericanGeophysical
Union.
Paper number IC0462.
0148-0227/81/001C-0462501.00
7267
Betweenthe tropopauseand 30 km the C2Hs mixing ratio
dropsmore or lesssteadilyby 3 ordersof magnitude.However, the uppermostsamples,although collectedduring descent,showelevatedC2H6mixing ratiosfor both •ghts. This
is a clear indication of C2H6 contamination. Since the other
trace gasesmeasuredfor theseflights do not show such a reversal in the vertical gradient, the elevated C2H6 concentration cannotbe ascribedto stratospherictransport.
There are various stepsin the sample collection and handling proceduresat which contaminationcan occur:(1) leakage in the vacuumlinesusedfor sampletransfer,(2) leakage
throughthe valvesof the samplecontainersduringstorage,(3)
outgassingof the various sample containers,(4) outgassing
from the inner walls of the cryogenicsamplerduring collection (e.g.,inlet line), and (5) outgassingfrom the externalsurfacesof balloonand payloadduring samplecollection.Points
I and 2 can be excludedwith somecertainty:Leakagewould
admix troposphericair to the stratospheric
samplesand would
causecontaminationin all tracegaseswith high troposphericstratosphericconcentrationdifferences.This has not been observed. Point 3, C2H6 outgassingof the sample containers,
seemsto be negligible,as shownby blank experiments.This
7268
RUDOLPHET AL.: STRATOSPHERIC
PROFILESOF C2H6 AND C3H8
œ, and the contaminationwill decreasewith decreasingaltitude at leastas 1/p. An estimateof contaminationdecreasing
as 1/p with altitude basedon the assumptionof externaloutgassingwith constant rate will therefore be rather con-
I
30-
ß
16 June 1979
servative.
20-
<[10 -
N
Applying this estimateto the actual flights and assuming
that the C•_H6measuredin the samplesat the secondhighest
altitudes (28.9 and 27.9 km, respectively)were completely
causedby contamination,the next lowest samples(26 km)
would have a contributionby contaminationof lessthan 30%,
and the lower samplesof lessthan 10%.The latter value is less
than the precisionof the gas chromatographicmeasurement.
This rapid falloff in contaminationwith decreasingaltitude is
-
also indicated by the rapid drop of a factor of 2--4 in mixing
ratio betweenthe highestand next highestsamplesobserved
C3H8 mixing ratio
during the flightsin June 1979(Figure 2). Although there reFig. 1. Vertical profile of the C3Hs mixing ratio measuredin the mains an element of uncertainty until the actual source of
lower stratosphereover southernFrance, 44øN latitude. Solid and contaminationis identifiedand removed,it appearssafeto asdashedcurvesrepresentmodel-predictedC3Hs profiles.
sumethat theC•_H•mixing ratios at and below 26 km are little
affectedby contamination.
leavesinternalor externaloutgassing
of C•_H6in flight as most
The stratosphericdata pointsshownin Figure 2 fall essenlikely sourcesof contamination.
tially on a straightline. Sincecontaminationbelow30 km altiIndeed,samplesfrom a balloonflight in November1979 tude is small, the measureddecreasein C•_H•mixing ratio is
over southernFrance, which had to be collectedduring ascent virtually exponential,certainlyup to 26 km altitudeand possirather than descentbecauseof limited flight time, showed bly up to 30 km altitude. A least squaresfit gives a scale
substantially
highermixingratiosof C•_H6and C3Hsthan height of 3.5 ñ 0.15 km for the decrease.It was calculatedexthosepresented
here,especially
above20 km altitude.This cludingthe contaminatedsamplesabove 30 km and the two
strongly
indicates
in-flightcontamination.
Thesedataalsoin- stragglingpointsat 18 and 22 km altitudefrom the profile on
dieatethat the C•_H6outgassing
rate dropsrapidlywith time, June 16, 1978.The fitted exponentialdecreaseis alsoshownin
about an order of magnitudeper hour.
Figure 2 (dash-dottedline).
10-11
10-10
10-9
Having narrowedthe likely sourcesto in-flight contamination,we cantry to estimateits extent.The samplecollectionrateof the cryosampler
is inverselyproportionalto the
DISCUSSION
Very few publisheddata coveringthe lower stratosphere
squareof theair pressure
p [Luebet al., 1975,Figure3]. Thus and upper troposphereare availablefor comparison.We
in the case of internal contamination the ratio of con-
couldnot find any other C3Hsmeasurements
for that altitude
taminationrateto samplingratewill decrease
with decreasing
rangein the literature,and for C•_H•the only measurements
sampling
altitudeat leastas 1/p•-evenif we admita constant published
seemto be thoseof ½ronnandRobinson
[1979a,b].
outgassing
rate.In thecaseof externaloutgassing
thereleased These authors measuredthe C2H• mixing ratio in about 60
contaminationwill be diluted with surroundingair of pressure
I
!
I
"--..
30-
ß 16June
1979
..,{era
)
ß•.,• -,,,
ß28June
1979
samplescollectedaboardan aircraftover the San Francisco
Bayarea(37øN)duringApril 1977at altitudesrangingmostly
from 2 km below to 3 km above the tropopause[½ronnand
Robinson,1979a]. The tropopausealtitude ranged between
11.3and 12 km. Despitea considerable
scatter,whichthe authorsascribedpartly to the experimentalimprecision,
the data
showeda clear and steepdecreaseof the C•_H•mixing ratio in
the lower stratosphere.
To avoid confusion,only the rangeof
the C2H6valuesby CronnandRobinson[1979a]is indicatedin
Figure2 by thehatchedarea.The presentdatafall well within
that range,indicatingreasonableagreementin the absolute
calibration.
<1:lO
I
,,,,,
10-12
•
,
,I
,
10-11
, ......
I
.........
10-10
I
10-9
I
......
10-8
C2H
6 mixingratio
Fig. 2. Vertical profilesof the C•_H6mixing ratio in the stratosphereoversouthernFrance,44øN latitude.The dash-dotted
line representsa least squaresfit of an exponentialprofile to the data excludingthe data in parentheses,
which are obviouslycontaminated.
The hatched area showsthe range of data by Cronn and Robinson
[1979a].The solid curve representsthe C•_I-]•profile predictedby a
one-dimensionalsteadystatemodel. The dashedcurveis a prediction
neglectingreactionof C•_H6with C1.
The rapid decreasein the C,_H6mixing ratio observedby
Cronnand Robinson[1979a]in the lower stratosphere
is contimed and extendedto higher altitudesby our measurements.
It is due to the fast destructionof C,_H6by C1 atomsand OH
radicals:
C•_H6
+ C1--> C,_H•+ HC1 Kl -- 7.3X10-l• exp(-61/2)
(g2)
C,_H6
+ OH -->C,_H•+ H,_O K,_-- 1.86x10-• exp(-1230/T)
[Manningand Kurylo,1977;Greiner,1970].
Similarly, C•H8 is destroyedby the reactions
RUDOLPHET AL.: STRATOSPHERIC
PROFILESOF C2H6 AND C3H8
!
(R3)
C3H8+ C1--• C3H7+ HC1 K3 = 3.2x 10- exp (-340/T)
(R4)
C3H8+ OH--• C3H7-I-H20 K4-- 1.4x10-!! exp(-675/2)
[Trotman-Dickenson
and Milne, 1967; Greiner, 1970].
At stratospherictemperaturesthe rate constantsfor the re-
[
7269
!
•
Cl ,-
• 20
'/'
action with CI are much faster than those for reaction with
OH. Thus reactionwith CI is a significantor even the dominant losspath in both cases,despitethe fact that the stratosphericconcentrationsof C1 are much lower than those of
OH. On the basisof model-calculatedvertical profilesof C1
and OH concentration(cf. Figure 3), 90% of the stratospheric
destructionof C2H6 is due to reaction with C1.
Becauseof its fast reactionwith C1 atoms the presenceof
C2H6 tends to lower the C1 concentration at those stratoo,;11
'
;,.,•,; •,,,
,.,+
'
e•lna•.•t•
o1.;.11,-14e
where.,C2H6is •,•sx•
presentIn s,ts-...•,a-• mlxing ratios[Aikin et al., 1979].This is alsodemonstratedin Figure 3 by the C1 profilespredictedfrom our one-dimensional
(I-D) steadystatemodelof stratospheric
chemistry:Below 18
km altitude the C1 profile influencedby C2H6 (dash-dotted
10
i
10•
• i1,,.I
•
102
• i •ll,11
,
103
, ,illill
,
10&
, Illlid
I
105
I , illill
,
106
, ......
107
Cbncenfrofion[moLecI cm3 ]
Fig. 3. Vertical profilesof CI atom and OH radical concentrations
in the stratosphere.The profilesC1½and OH½were calculatedfrom a
one-dimensional steady state model. The calculated CI profile
changesto the dash-dottedcurve when the presenceof C2H6 is taken
into account.The upper limit for the CI concentrationestimatedfrom
the measuredC2H6 data is given by the dashedcurve.
curve)fallssignificantly
belowtheC1profile,whichneglectstitudethe measured
mixingratiois I orderof magnitude
thepresence
of C2H6(solidcurve).Themaximum
reductionhigherandat 25 km altitude,2 ordersof magnitude
higher
of abouta factorof 3 isreached
around
thetropopause.
Ow- thanthemodel-calculated
values.
Sucha comparison
couldbe
ingtothesteep
decrease
of C2H•in themodel,itsinfluence
on questioned.
Themodel,whose
transport
hasbeenreduced
to
the C1 profile above 18 km is negligible.
The presenceof C3H8 also reducesthe C1 concentration.
The reductionis largestaround the tropopause,about 40%,
and dropsrapidly with increasingaltitude. Above 14 km altitude the effectis negligible.The effectof C3Hsis not included
in the C1 profilesshownin Figure 3.
The C1 and OH profiles in Figure 3 were calculated for
spring,45øN latitude,and a tropopausealtitude of 11 km, in
order to match the averagesolarflux, temperature,and transport conditionsprevailingduring the time of samplecollection. They are diurnally averaged.The total chlorinemixing
ratio (C1, C10, C1ONO•, and HC1) in the model is 2.5 ppb at
30 km altitude.The model utilizesthe chemistryand rate constantsdescribedby Hudsonand Reed [ 1979].The detailshave
been describedelsewhere[R6th et al., 1980]. Both C1 and OH
profilescomparefavorablywith thosepredictedby other I-D
modelsusing similar chemistry[cf. Chameidesand Cicerone,
1978;National Academyof Sciences,1979;J. S. Chang, private
communication,1979].
The model calculationsalso predictedthe C•H• and C3Hs
profilesat 45øN. The abovereactionswere the only destruc-
simplevertical eddy diffusion,constructsa temporallyand
horizontally averagedprofile, whereasthe experimentalprofiles are subjectnot only to temporal variationsin the local
C2H• mixing ratio but alsoto fluxes,which can have vertical
and horizontal, turbulent and advective components. It is
likely that the measuredC•H• data do deviateto someextent
from the localaverage,certainlyfrom the globalaverageas it
is definedby a I-D model. The questionis whether a local
and temporarytransportperturbationcan enhancethe C•H•
mixingratioby asmuchasis observedhere.If not, we haveto
admit the possibilityof a lower stratospheric
destructionrate
of C2H•.
To that end, the variousmodelsof transportneedto be discussedand checkedagainstthe available information. We
firstnotethat the experimentaldata consistof two setswhich,
althoughsampledabout 2 weeksapart, superimposequite
well to form the samegeneralprofile.The temporalvariations
were small at most altitudes. On the other hand the model-
calculated lifetimes of C•H6 for chemical destruction, •, is
ditionsat thegroundwerebasedon measured
mixingratiosat
mid-latitudes:2 ppb for C•H• and 0.4 ppb for C3Hs.The predicted profilesare also includedin Figures 1 and 2 (solid
curves).In orderto demonstrate
the importanceof the reaction with C1 atoms,profilesneglectingthe C1 reactions,(R l)
and (R3), were alsocalculated(dashedcurves).
The C3Hsdata (Figure 1) are too few at presentto warrant
detailedinvestigation;
nevertheless,
within the observedscatter and experimentalerror the data and predictedprofiles
short.It decreases
from 20 daysat 20 km altitudeto 2 daysat
30 km altitude(Figure4). Thusif the profilecollectedon June
16, 1979, had been due to a momentaryperturbationof the
modeledaverageprofile, the mixing ratios in the upper part
should have relaxed toward that averageprofile by June 28,
1979,when the next profilewas collected.Sucha relaxation
was not observed.Either stratosphericdestructionof C2H•
was much slowerthan was predictedby the model,or it was
matchedby a large divergenceof the C•H• ttux. In any case
the transportpattern which establishedand maintainedthe
measuredC•H• profile must have persistedlonger than the
C•H• lifetime at the higheraltitudes,at leastfor a few weeks.
With that, one mode of transportcan be dismissedas unlikely. Transportby a meanverticalwind componentwould
seem to agree.
requirevelocities
around2 cm/s at 30 km and 0.5 cm/s at 25
tion pathsincludedfor the higherhydrocarbons;
reactionwith
OlD remains negligible.There are no known production
mechanismsfor C•H• in the stratosphere.
The boundarycon-
km altitude to maintain the observedC•H• profile against a
they showa significantand systematic
deviationovera large destructioncharacterizedby %. Persistenceof that mode for
The C2H6data are much more interestingin the sensethat
altituderangefrom the rapid decreasepredictedby the I-D
steadystatemodel.The deviationis ratherlarge:At 20 kmal-
severalweekswouldpushthe mixingratiosof the longer-lived
tracegasesCFL, N20, CF•CI•, andCFC13at 25 or 30 km alti-
7270
RUDOLPHET AL.: STRATOSPHERIC
PROFILESOF C2H6 AND C3Hs
,o
w i ' ' ' '"!
,o
'i
,o ,seFo,n,ds,,
'
12 ' , , '1'1
I•hz
• Kz
30
-•
•.,.•..
20-
-
•0-
1
10
•00
Lifelimeof [2H6 [days]
00
on any transport-caused
deviationfrom the averageC2H• profile. CFCI3 and CF2C12reach vertical gradientsand chemical
lifetimes in the middle stratospheresimilar to the ones of
C2H6 in the lower stratosphere.In fact, at mid-latitudes the
measuredgradientof CFCI3 approachesthe model-calculated
one of C2H6 already at 20 km altitude. The lifetime of CFCI3
is 1 month at 30 km altitude. Therefore by analogy,C2H• profiles in the lower stratosphereshould respond to similar
changesin the transportwith similardeviationsfrom the average,as do CFCI3 and CF2C12in the middle stratosphere.
The
scatterof the CFCI3 data shouldprovide an estimatefor the
expecteddeviationsfrom the average C2H• profile. The observedCFCI3 and CF2C12mixing ratios around and above 30
km altitude deviate not more than a factor of 5 from the mea-
sured average[Fabian et al., 1979b].This should representa
reasonableupperlimit on the transport-caused
deviationfrom
the averageC2H• profile. The limit is conservativebecauseit
rfpr½sfms
•½ modelprfdi•io•, •d ½•is d½fi•½d
from•½ mccared includes the error of the CFCI3 measurement, which becomes
CzH•profile.T•½lfad•8 •½• of ½½,
•z/K,, is alsos•o•.
quite large for the smallconcentrations
above30 km altitude.
The upperlimit of a factorof 5 is muchlessthan the deviation
tudeto muchhighervaluesthan wereactuallyobservedin the betweenmeasuredand model-calculatedC2H• profiles,which
presentflights[Fabianet al., 1979b].
has increasedto a factor of 100 at 25 km altitude (cf. Figure
Increasedvertical eddy diffusionis not soreadily dismissed. 2).
In this case, which implies vertical mixing, the time with
None of the argumentsgivenaboveis sufficientlystrongto
which the profile respondsto a changein transportrate de- excludetransportas being at least partly responsiblefor the
pends on the chemical lifetime of the molecule considered. deviation betweenmeasuredand calculatedC2H6 profiles.In
Since C2H6 is much shorterlived, its profile might have ap- fact, suchdeviationsare to be expected.However, becausethe
proacheda form suchas that measuredwithout a noticeable, difference between the measuredC2H• profile and the one
simultaneouschangein the measuredCH4 or N20 profiles.To predictedby the I-D steadystatemodelis so large,it is diffimaintain the observed C2H6 profile, values of the vertical cult to blame it all on a peculiar transport pattern. More
eddy diffusion coefficient4 times higher than those used in likely, the model-calculateddestructionrate of C2H• is overour I-D modelare required,that is, Kz -- 3 x 10• cm2/sat 20 estimated.Becausereactionwith OH contributesonly 10%of
km and Kz -- 2 x 105cm2/s at 30 km altitude. Such values, the total destructionabove 20 km altitude, that reaction path
however, are rather high for the seasonand latitude consid- can be excluded.Apparently,the measuredC2H• profile deered [cf. ClimaticImpact Assessment
Program, 1975;$chmelte- mandsa lower CI concentrationthan that predictedby our or
kopfet al., 1977]and are not likely to persistfor a long time.
other present I-D models,sincethe reaction rate constantK,,
Finally, we have to considerhorizontal flow. This possi- by Manning and Kurylo [1977],usedhere appearsto be essenbility still requiresfast upward transportsomewhere,to gener- tially correct. Except for an old measurementby Ferrisand
ate high C2H• concentrationsat higher altitudes. Further- Knox [1964] which gave a rate constantnearly a factor of 2
more, the samplingflightswere launched during a period of slower,the publisheddata of Daviset al. [1970]and Baulchet
weak easterlyflow in the stratosphereover the Eurasian conti- al. [1980], who cited unpublisheddata of R. J. Lewis et al.
nent which persistedduringmostof June,as evidencedby the (1980), R. T. Watsonet al. (1980), and R. T. Watson and G.
constantpressurechartsbetween50 and 10 mbar. This leaves Ray (1980), agreewith the measurements
of Manningand Kulittle chancefor large-scale,horizontal transportfast enough rylo [1977]to betterthan 20% for the whole stratospherictemto overcome the fast model-calculated
destruction and inperaturerange. To explain the observedC2H• profile, the rate
crease the local C2H• mixing ratios to the observedvalues. constantK, would have to be slowerby a factor of 4.
There is, however,someindication that horizontal transport
Becausethe measuredC2H6profile in Figure 2 may differ
can causefluctuationsin the observedmixing ratios. Many considerablyfrom the globalaverage,a definiteprofile of the
stratosphericprofilesof the longer-livedsourcegases,for ex- CI atom concentration cannot be derived. To estimate how
ample, CH4, N20, and CF2C12 measured over southern muchthe CI concentrationin the lower stratosphere
may difFrance, and the presentonesare no exception,show mixing fer from the model-predictedone, we proceedwith the asratios slightly (about 10%) but systematicallyincreasedover sumptionsthat the measuredC2H• profile representsthe
the latitudinal average at 25-30 km altitudes. Though less global averageand that transportcan be describedby vertical
pronounced,the feature is very similar to that observedover eddy diffusionas in the I-D model. With that we can estimate
30øN latitude and has been ascribedto meridional transport the verticalflux divergenceof C2H•, which in steadystateis
[Ehhalt and T6nnissen,1979]. On the average,however, this balancedby the destructionrate of C2H•. It is expressed
as the
mode of transportseemsslow, since H2 which is produced inverseof the destructiontime, or chemical lifetime, 'r•:
during the destructionof CH• on a .time scaleof years is also
slightly increased.Becauseit is a relatively slow processand
becausethe fluctuations.induced by it on the longer-lived
trace gasesare small, meridional transport is not likely to
where M is the measuredC•H• mixing ratio, p the number
causethe large discrepancyobservedin the C2H• profile.
usedin our
There is also a more generalargumentwhich placesa limit densityof air, andK, theeddydiffusioncoefficient
pM' a• p' K,.
=K,[CI]
+ K•[0H] (1)
RUDOLPHET AL.: STRATOSPHERIC
PROFILESOF C2He AND C3Hs
model.The resulting(experimental)
•r is shownin Figure4.
Sincethe measuredmixingratioprofilefitsan exponentialdecreasewith a scaleheighth -- 3.5 :i: 0.15km (seeabove),the
heightdependence
of •r is dominatedby that of p and K,; •
isoftenapproximated
by ha/K,,whichis alsoshownin Figure
4. Fromit the form of our K, profilecanbe easilyderived.For
7271
cence,is restrictedto higheraltitudes.EventhoughCIO can
be measuredto as low as 25 km altitude,the resonancefluorescence
techniquedoesnot providemeasurements
of atomic
CI below35 km altitude[Anderson
et al., 19'/7].For this rea-
sonthereis alsono altitudeoverlapwith our estimateof CI
from Cartemeasurements,
and thusa directcomparisonwith
comparison the model-predicted lifetime of CaH• is also the CI data by Andersonet al. [1977]is not feasible.Becausea
shownin Figure 4. It is givenby
considerable
fraction,aboutonehaft, of the O3destruction
by
CIOx proceedsbelow 30 kin, the implicationof lower CI concentrationsat theselower altitudesis important in the estimate of anthropogenicperturbations,and a measurementof
wherethe quantitiesto the rightare all takenfrom the model. the CI at theselower altitudesis of great interest.If the prob-
?,,-'
--K,[CI]½
+Ka[OH]½-I ez
ct[ r,. ctM,,]
ezj (2)
The comparisongivenby Figure4 showsclearlythat ?• is lem of contamination can be overcome, which seemsfeasible,
of CaH• by our techniquecouldprobablybe
substantiallylongerthan •½above 14km altitude. In the lower the measurement
extended
to
35
km
and provide data for calculationof an avstratosphere
the experimental
lifetimesof CaH•,?•, rangebetween 200 and 20 days,which would alsotend to decreasethe erageverticalCI profilein the lower and middle stratosphere.
transport-caused
deviations
from
theaverage
Calls
profile.Acknowledgments.
Wewould
like
tothank
P.Fabian
ofthe
MaxObviously,
theexperimentally
deduced
destruction
rateof Planck-institut
farAeronomie
in Lindau,
whomade
available
the
Carteby CI issmallerthanthatpredicted
bythemodel.In or- stratospheric
samples.
Likewise,
we thankW. Seilerof theMaxderto obtainan estimatefor the CI profilethat wouldexplain Planck-Institutfar Chemie in Mainz, who providedthe tropospheric
our Call6measurements,
we useequation(1); • is takenfrom samples.This paper is dedicatedto K. H. Lieser in honor of his sixtieth birthday.
Figure4, and K• from Manningand Kurylo[1977].Reaction
with OH is neglected.Consequently,
the C1concentrations
are
REFERENCES
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and the derivedCI profile presentsrather an
A. C.,J.R.Herman,
andE.J.Maier,Ethane
andethylene
beupperlimit. It is shownin Figure3 as profileCI. The CI con- Aiken,
Proceedings
of the NATO Advanced
centrations
derivedfromthe measured
Call6are considerably haviourin the atmosphere,
StudyInstituteon Atmospheric
Ozone,AldeiadasAcoteias,
Porlower(up to a factorof 10)than the model-predicted
profile.
tugal,Rep.FAA-EE-80-20,
pp. 191-208,Fed. Aviat. Admin.,
Below 20 km altitude an increasingfraction of Call6 reacts
Washington,D.C., 1979.
G. J., J. J. Margitan,andJ. H. Stealman,
Atomicchlorine
with OH. There the neglectof reactionwith OH leadsto a Anderson,
andchlorine
monoxide
radicalin thestratosphere:
Threein situobconsiderable overestimate of the CI concentration, which
servations,
Science,198, 501-503, 1977.
causes
thederived
upper
limittocurve
tohigher
CI concentra-Baulch,
D. L., R. A. Cox,R. F. Hampson,
Jr.,J.A. Korr,J.Troe,and
tions.Introductionof the new reactionrate for OH and HNO3
[Wine et aL, 1981] would decreasethe model-calculatedCI
R. T. Watson,Evaluated
kineticandphotochemical
datafor atmosphericchemistry,
J. Phys.Chem.Ref. Data, 9, 425, 1980.
W. L.,andR. J.Cicerone,
Effects
ofnonmethane
hydroprofilein the lowerstratosphere
by a factorof 1.5-2 (S. Liu, Chameides,
carbons
in theatmosphere,
J. Geophys.
Res.,83,947-950,1978.
private communication,1980). Even so, the derived upper
Climatic
ImpactAssessment
Program,
ClAPMonograph
I: TheNatlimit remainsconsiderablylower than the model-calculated uralStratosphere
of 1974,Rep.DOT-TST-75-51,
Dep.of Transp.,
Washington,D.C., 1975.
CI profile.Clearly, if subsequent
measurements
give a global
Call6 profile similar to the present measurements,a sub- Cronn,
D., andE. Robinson,
Tropospheric
andlowerstratospheric
stantial revision of the CI concentration in the lower strato-
verticalprofilesof ethaneandacetylene,
Geophys.
Res.Lett.,6,
641-644, 1979a.
spherewill be required.The aboveC1concentrations
are averCronn,
D. R.,andE. Robinson,
Determination
oftracegases
in Learagesover the lifetime of Call6. Becausetransportwithin the
jetandU-2whole
airsamples
during
theIntertropical
Convergence
estimatedlifetimesof CaH• (20-200 days) can be extensive,
ZoneExperiment,
1977Intertropical
Convergence
ZoneExperiment,NASA Tech.Memo, TM 78577,61-65, 1979b.
the CI valuesshouldalsorepresenta large-scale
horizontalav-
Davis,
D. D.,W.Braun,
andA.M. Bass,
Reactions
ofC1aP3/a:
Absolute
rate
constants
for
reaction
with:
Ha,
CH4,
CaH•,
CHaCIn,
C-aCln
Given the preliminaryand limited natureof the CaH• data,
'andc-Celica,
Int. J. Chem.Kinet.,2, 101,1970.
much of the foregoingdiscussion
is somewhattentative.Nev- Ehhalt,
D. H., andA. T6nnissen,
Hydrogen
andcarbon
compounds
ertheless,
the presentanalysisshowsfor our assumptions
and
in thestratosphere,
Proceedings
oftheNATOAdvanced
StudyInstitute
onAtmospheric
Ozone,
AldeiadasAcoteias,
Portugal,
Rep.
for one particularcasethat the averageCI concentrationin
erage.
FAA-EE-80-20,
pp. 129-152,
Fed.Aviat.Admin.,Washington,
D.
the lowerstratosphere
is lowerthan that predictedby current
C., 1979.
models.It is interestingto notethat the CIO measurements
by Fabian,P.,R. Botchers,
K. H. Weiler,U. Schmidt,
A. Volz,D. H. EhAndersonet al. [1977]in the lower stratosphere
also give valhalt,W. Seiler,andF. Milller,Simultaneously
measured
vertical
profiles
of Ha,CH4,CO,NaO,CFCI3,andCFaCIain themid-latiues lower by up to a factor of 5 than the I-D model calcustratosphere
andtroposphere,
.L Geophys.
Res.,84,3149-3154,
lations.The analysisalso showsthat extensivestratospheric tude
1979a.
CaH• measurements
of sufficientaccuracyare a usefultool for Fabian,P.,R. Borehers,
K. H. Weiler,U. Schmidt,
A. Volz,D. H. Ehdeterminingthe averageCI concentrationin the lower stratohalt,W. Seiler,
andF. Miiller,Thevertical
distribution
ofHa,CH4,
sphere.
NaO,CFC13andCFaCIaat midlatitudes,
paperpresented
at 17th
GeneralAssembly,
IUGG, Canberra,
Australia,
Dec.2-15, 1979b.
CONCLUSION
Fettis,
G. C.,andJ.H. Knox,Therateconstants
ofhalogen
atomreactions,Prog.React.Kinet.,2, 1-38, 1964.
N. R.,Hydroxyl
radical
kinetics
bykinetic
spectroscopy,
V.
It has been shownthat the measurementof Call6 can be Greiner,
Reactions
withalkanes
in therange
300-500
K, J. Chem.
Phys,,
53,
usedto derive profilesof atomic chlorine in the lower strato1070-1076, 1970.
sphere.This is especiallyinteresting,becausethe only avail- Hudson,
R. D., andE. J. Reed(Eds.),Thestratosphere:
Present
and
able techniquefor measuringCI directly, resonancefluoresfuture,NASA Ref. Publ., 1049, 1979.
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