GEOPHYSICALRESEARCHLETTERS,VOL. 27,NO. 17,PAGES2605-2608,SEPTEMBER1, 2000
Ozonedestructionand productionratesbetweenspringand
autumn in the Arctic stratosphere
D. W. Fahey1,2,
R. S.Gaol,2,
L. A. DelNegro3,
E.R.Keim4,
S.R. KawaS,
R.J.
Salawitch6,
P.O.Wennberg7,
T. F. HaniscoS,
E. J.LanzendorfS,
K. K. PerkinsS,
S.A.
Lloyd9,
W. H. Swartz9,10,
M. H. Proffittl,2,
J.J.Margitan6,
J.C.Wilson11,
R.M.
StimpfieS,
R.C.Cohen12,
C.T. McElroy13,
C.R.Webster6,
M. Loewenstein14,
J.W.
Elkins3,T. P. Bui14
Abstract. In situ measurements
of radicalandlong-livedspecies
were made in the lower Arctic stratosphere(18 to 20 km)
03 destructionand productionprocesses
Stratospheric
03 abundances
representa balancebetween
betweenspringand early autumnin 1997. The measurementsdestruction
andproduction
processes
andtransport.Thereactions
include
0 3, C10,OH, HO2,NO, NO2,N20, CO, andoverhead listed in Table 1 representthe principal chemical processes
03. A photochemical
boxmodelconstrained
bytheseandother controlling03 productionanddestruction
in the lower summer
observationsis used to compute the diurnally averaged stratosphere
[Nevison
et al., 1999;Laryet al., 1997]. Ozoneis
destruction
andproduction
ratesof 03 in thisregion. The rates destroyedin catalytic cycles involving nitrogen,hydrogen,
showa strongdependence
on solarexposure
andambient03. chlorine,and brominespeciesand in reactionwith O atoms.
Total destruction rates, which reach 19%/month in summer,
Ozoneproduction
occursprimarilythroughoxygenphotolysis
revealthe predominant
role of NOx andHOx catalyticcycles (R14). Production
termsfrom CO andCH4 oxidationare small
throughout
theperiod. Production
of 03 is significant
onlyin and are neglectedhere. The destruction
andproduction
terms
midsummer
air parcels.A comparison
of observed
03 changes associated
with theprocesses
in Table 1 aregroupedin Table2.
with destructionrates and transport effects indicates the The groupingby reactivefamily is not uniquesince some
predominant
roleof destruction
in spring
andanincreased
roleof catalyticcyclesinvolvereactivespeciesfrom more than one
transportby early autumn.
family. Thetermsuse[X] for theconcentration
of species
X, ki
for the kinetic rate coefficientof Ri, Ji for the photolysisrate
Introduction
coefficient
of Ri, andCi for branching
terms.The 03 destruction
ratesfor an air parcelareobtained
by integration
Measurements
of a wide rangeof reactiveand long-lived andproduction
species
wereobtained
in thelowerstratosphere
usingtheNASA of the termsin Table 2 over a diurnal cycle. In additionto rate
coefficientsand pressure,the integrationrequiresthe diurnal
ER-2high-altitude
research
aircraftaspartof thePhotochemistry
abundances
of 12 species:OH, HO2, NO, NO2, C10, BrO,
C1ONO2,
BrONO2,
O, 02, 03, andCO.
projectin 1997. POLARISwasdesigned
to explorethedecrease
of Ozone Loss in the Arctic Region In Summer(POLARIS)
of 0 3 thatoccurs
between
springandautumnat northern
high
latitudes[Newmanet al., 1999;FaheyandRavishankara,
1999]. Observed and derived parameters
Ozonedestruction
andproduction
ratesin sampledair masses
are
Measurements
providedby instruments
on boardthe ER-2
calculated
usinga photochemical
box modelconstrained
by the aircraft are used directly and indirectly to constrain a
available in situ and remote observations.
photochemical
box modeland the integrationof diurnalO3
change.ThoseusedhereareNO, NO2,OH, C10,CO, O3,NOy,
N20, halon-1211,
CFC-11,SF6,surface
area(SA) of background
1Aeronomy
Laboratory,
NationalOceanicandAtmospheric
Administration, Boulder, CO
2Cooperative
Institute
forResearch
in Environmental
Sciences,
Universityof Colorado,Boulder,CO
3NOAA ClimateMonitoringandDiagnostics
Laboratory,
Boulder, CO
4TheAerospace
Corporation,
LosAngeles,CA
5NASA GoddardSpaceFlightCenter,Greenbelt,MD
6NASAJetPropulsion
Laboratory,
Pasadena,
CA
7Divisionof GeologyandPlanetarySciences,
California
Instituteof Technology,Pasadena,
CA
8Department
of Chemistry,
HarvardUniversity,
Cambridge,
MA
9TheJohnsHopkinsUniversityAppliedPhysicsLaboratory,
Laurel, MD
10Department
of Chemistry
andBiochemistry,
University
of
Maryland,CollegePark,MD
1•Department
of Engineering,
Universityof Denver,Denver,
CO
12Department
of Chemistry,
Universityof California,
Berkeley,CA
13Atmospheric
Environment
Service,Downsview,
Ontario,
Canada
14NASA Ames ResearchCenter, Moffett Field, CA
Copyright
2000bytheAmerican
Geophysical
Union.
Papernumber2000GL011404.
0094-8276/00/2000GL011404505.00
sulfate aerosol, overhead O3 column, effective surface
reflectivity,pressure
(P), temperature
(T), latitude,longitude,
and
measurement
time. The sourceand uncertaintyfor mostof these
in situ measurementsare describedelsewhere[Del Negro et al.,
1999; Gao et al., 1997; Herman et al., 1999]. An air parcelis
definedby a 100saveragemeasurement
alongthe flight track
when the solarzenith angle(SZAs) is lessthan 85ø. The full
diurnaldependences
of OH andC10 are estimated
for eachair
parcelby scaling
theSZArelationships
in Wennberg
etal. [1994]
to therespectiveair parcelmeasurement.
Photolysis
ratecoefficients
for anair parcelareavailablefrom
two independent
calculations
[Salawitchet al., 1994;Swartzet
al., 1999]. Both calculations
usea spherical,isotropicmultiplescattering
modelof theatmospheric
radiationfield,incorporating
photolysis
cross-sections,
observed
overhead
03 (columnamount
abovethe aircraft),andsurfacereflectivity. Changesin overhead
0 3 vary from climatologicalvaluesalong the flight track,
significantlyaffectingthe local radiationfield. The j values
calculated
for POLARIS generallyshowgoodagreement
(+_15%)
with eachother[Del Negroet al., 1999]. Valuesofjls, 03, and
pressure
arecombined
to calculate
thediurnaldependence
of O
atomsusingthesteadystaterelation[O] = j15103]/k16102][M].
A diurnalphotochemical
box modelis usedhereto calculate
the diurnaldependence
of NO2, HO2, C1ONO2,BrONO2,and
2605
2606
FAHEY ET AL.: OZONE MEASUREMENTS IN THE ARCTIC STRATOSPHERE
Table 1. Reactions
usedin diurnalintegration
of 03 change.
1
2
3
4
OH+O3 -->HO2+202
HO2+O3 -->OH+O2
C10+HO2 -->HOCl+O2
BrO+HO2 -->HOBr+O2
10
11
12
BrO+C10-• Br+CI+O2
BrONO2+hv-• Br+NO3
NO2+O(3p)_,xNO+O2
13
O(3p)+o3_,x202
(panelsG- I) which rangefrom 0.3 to 1.3 partsper billion by
volume
(ppbv).SinceNOyvalues
arenearlyconstant
(panels
JL), theNOx/NOyratiochanges
in a similarmanner
to NO2. The
enhanced
valuesof NO2 and NOx/NOyin midsummer
are
attributedto the extent of continuousSE that occursat high
latitudes near solstice [Farman et al., 1985; Fahey and
5 C10+O(3p)-->CI+O2
14 O2+hv-• 20(3p)
Ravishankara,1999; Gao et al., 1999]. Continuousexposureof
6 C1ONO2+hv-->CI+NO3
15 O3+hv _,xO(3p)+o2
stratospheric
air parcelscausesN205 productionto ceasebecause
7 NO3+hv-->NO+O2
16 O(3p)+O2+M-• O3+M
NO3, the intermediatein the productionof N205, is rapidly
8 NO3+hv-->NO2+O
17 OH+CO+O2 -,, HO2+CO2
photolyzed.
9 BrO+O(3p)-->Br+O2
18 ' HO2+NO --> OH+NO2
After NOx, HOx cyclesare the next largestcontributor(2040%) to 03 destruction rates in all phases. The smallest
contributions
arefrom the C1/BrandO cycleswhichsumto about
BrO. Themodelincludes
theNOyinterconversion
reactions
as 20% in the spring and midsummerand slightly more in early
usedby Gaoet al. [1999]to simulate
theNOx/NOy
ratioin autumn. The averagemixing ratiosof HO2, C10, and BrO are all
POLARIS. All rate coefficientsare from DeMore et al. [1997] lessthan0.03 ppbv and significantlylessthanNO2 values(panel
exceptfor the OH + HNO3, OH + NO2, andNO2 + O reactions G- I). The largestabsolutevaluesof the HO2 andC1/Brradicals
[see referencesin Portmannet al., 1999]. ObservedSA values and their largestcontributionto 03 destructionoccurin early
(0.5 - 1.5 !am2cm-3)are includedin the modelto determinethe autumn. This is consistentwith minimum values of NO2
rateof the heterogeneous
reactionsN205 + H20 andBrONO2 + observedin late summerbecauseNOx moderatesthe abundance
H20 [DeMore et al., 1997]. Other heterogeneous
reactionsare of thesespecies[e.g.Nevisonet al., 1999;Wennberget al., 1994].
not importantat POLARIS temperatures(~ 220 - 230 K) [Del
Forcedincreasesin NOx at constantNOy do not
Negro et al., 1999]. Initial BrO concentrationsfor the box model proportionatelyincreasemodeled03 loss in the high-latitude
areprovidedby calculations
of the steadystatepartitioningof the summerstratosphere
becauseof the NOx moderatingeffecton the
Bry reservoir. Bry in an air parcelis estimated
from the other losscycles [Nevisonet al., 1999]. This was also confirmed
measurementsof N20, halon-1211, CFC-11, and SF6 as
with selected box model runs in the POLARIS
describedin Wamsleyet al. [1998]. The box model includesthe
principal inorganicbromine speciesand their interconversion
reactions[Lary et al., 1996].
The box model is constrainedby measuredC10, the diurnal
POLARIS destructionratesdependmore fundamentallyon 03
and SE as shown in Figure 2 for the data in Figure 1. The
positive correlationof the rates with 0 3 at constantSE is
data set.
The
intriguing feature of the entire POLARIS data set. A similar
dependence
of OH,andconstant
values
of 03, SA,Bry,P, andT. correlationis also found separatelyin eachphase. Underlying
Themodelis initialized
withmeasured
NO andNOyandwith this correlation are the overall positive correlations of the
approximate
steadystatevaluesof NO2, C1ONO2,N205, HNO3,
HO2, and BrO. Good agreementhas generally been found
betweenmeasuredand steadystatevaluesof NO2, C1ONO2, and
HO2 in thelowerstratosphere
[Del Negroet al., 1999;Stimpfieet
al., 1999; Wennberget al., 1994]. The modelis integratedover
24 hrsfrom the measurement
time usinga 100stime step. After
24 hrs,outputvaluesof N205, C1ONO2, HNO3, andBrO andthe
initialinputvaluesof NO andNOyareusedto reinitialize
the
model. Integrationand reinitialization occursfor additional24-
daytime-averaged
abundances
of NO2, HO2, andC10 with 03 in
thedataset(figuresnot shown).At constant03 in Figure2, total
destructionrates increase with SE. The SE changesare a
combination of latitudinal and seasonal differences which are not
separablehere (Figure 1). Diurnally averageddestructionrates
will in general dependstrongly on SE since it increaseswith
length-of-dayand sincedestructionand productionratesare zero
at night. The extentto whichthe 03 andSE dependences
found
hereapplyto otherregionsof the stratosphere
mustawait further
hourperiods(about6) until furtherchangesin N205, C1ONO2, study.
HNO3, and BrO valuesare negligible. With the model results
The decreasein 03 valuesin the POLARIS aircraft data set
and otherparameters,03 destructionand productionratesin an (60 - 70øN, 18-20 km) are very consistent(absolutevaluesand
air parcelare obtainedby integrationof the respective
processes month-to-month changes) with those in the more extensive
in Table 2 overa diurnalcycle.
Results
The modelandobservational
resultsare shownin Figure1 for
the spring,midsummer,and early autumndata as a functionof
latitude. Average total 03 destructionrates at 18 to 20 km
(panels AC) are approximately 5%/month or greater
throughout the data set with a maximum of about 19%/month
above80øNin midsummer.The total destruction
rate is offsetby
03 productionto yield the net destructionrate. The net 03
destructionratesare positive(decreasing03 tendency)for all of
POLARIS exceptfor low latitudesin midsummer(panelB). The
solarexposure(SE) valuesshownin panelsD throughF are the
fractionof time that the SZA for an air parcelhasbeenlessthan
93ø in the past 1 or 5 daysas calculatedusingback trajectories.
SE valuesmaximize in midsummer,reachingunity (continuous
illumination)for parcelsfoundpolewardof 65øN. The difference
between 1 and 5 day SE values is significant only for high
latitudesin spring.
The fractionalcontributionsto the total rates(panelsD- F)
by NOx, HOx, C1/Br, and O processesindicatesthe predominant
role of NOx, particularlyin the midsummerphase. The NOx
contributioncorrelateswell with the averagedaytimeNO2 values
satellitedata sets[Rosenlof, 1999] and with the sonde/satellite
climatology for 1988 to 1996 [Logan and McPeters; 1999].
Average03 valuesfor 18 - 20 km for themonthpairsApril-May,
June-July,andAugust-September
are 2.6, 2.1, and 1.9 partsper
millionby volume(ppmv),respectively,
from POLARIS and2.4,
1.9, and 1.8 ppmv,respectively,from the climatology. The 03
decreasesin the aircraft data set are proportionatelysimilar to
Table 2. 03 destruction
andproductionterms
Destruction
Term
by HOx
by NOx
by C1/Br
byO
{Clkl [OH]+k2[HO2]}[03]
2 k12[NO2][O]
2 (j7/(j7+Js)){ j6[C1ONO2]+jii[BrONO2]}
(1+C2){k3[C10]+k4[BrO] } [HO2]
2{ks[C10]+k9[BrO]}[O]+ 2 kio[C10] [BrO]
2k1310][O3]
Production
Term
by 0 2
2 J14102]
HereCl = k2103]/{k18[NO]+k2103]+k3[C10]+k4[BrO
]}
andC2 - kl[O3]/{k17[CO]+kl[O3]}
FAHEY ET AL.' OZONE MEASUREMENTS
Phase1, April 22 - May 13
o
• 1.o
i I ,
'=
I
•0.8
IN THE ARCTIC STRATOSPHERE
Phase2, June26 - July 7
•...........
!..........
D'. •el
I
2607
Phase3, September8 - 23
•i ..lll_•[;$111111111111111111114111111111
/
/ /•
'[ • NO• • C1& Br[•
.....
::2•
..............
I • HOx
m•+O
¸
• 0.4
ß•- 0.2 - •
•
0.2
• 0o0
oo
30•
1.5
2o •
•o•
0.0
o
3.0
lO 2:
2.5
c72.o
1.5
o
50
60
70
80
90
50
60
70
80
90
50
60
70
80
90
Latitude(degrees)
Figure 1. Observationaldata and resultsof the photochemicalbox model calculationsas a functionof northernlatitudefor the three
phasesof POLARIS. The total destructionrate is offset by the productionrate to obtainthe net destructionrate. Data are averagesof
sampledair parcelsfound in 5ø latitudebins for ambientpressuresbetween50 and 80 hPa (-- 18 - 20 km). The numberof flights and
100s datapointsincludedin eachphaseare, respectively,9 and 600; 4 and 590; 6 and 530. More than one-half of the data pointsare
obtainedbetween60øN and 70øN latitude in eachphase. The lines in panels(D-F) are the calculated1-day (thick-dashed)and 5-day
(thin-dashed)solar exposure(SE) factors. Panels(D-F) representthe fractionalcontributionof the destructionprocessesin Table 2 to
the total destructionrates. Panels (G-I) show the calculateddaytime averagemixing ratio of key radical speciesas used in the box
model.Panels(J-L)showaverage
observed
0 3 andNOy. Theverticalbarsshowthesamplevariance
in eachlatitudebinfor the
respectiveparameters.Ozonevaluesare expressedaspartsper million by volume(ppmv).
decreasesin the associated0 3 column amounts[Newmanet al.,
1999].
The net chemicaldestructionratesin Figure 1 for 60- 70øN
havebeencomparedwith observed03 changesandthoseinferred
from modeled transport terms [Rosenlof, 1999]. In spring and
midsummerthe net destructionratesand observedratesof change
role only in the Arctic summer period. The results show the
predominanceof the NOx catalytic cycle over the HOx and
C10/BrO cycles, arising from enhanced solar exposure. The
(%/month)
areverysimilar.In earlyautumnthenetchemical
destruction
rateexceedsthe observed
rateof change.Transport
processes
arefoundto increase
0 3 morestronglyin earlyautumn
thanspring.A quantitative
comparison
indicatesthatspringand
midsummer0 3 changesare dominatedby chemicaldestruction
g 25 "
•'
0.6
0.7
0.8
SE
09
1.0""
mI
20
whereastransport
dominates
in early autumn. Independent
evidence
for thepredominant
roleof chemically
induced
03
• 15
changes
in springandsummer
comesfromanalysis
of theO3/HF
column
abundance
ratios
[Toon
etal.,1999]
and
fractal
analysis •
of the0 3 datatime series[Tucket al., 1999].
Summary and conclusions
10
!
,
l,
,
I
,,,
I
1.5
2.0
2.5
3.0
In situ observations
of radicaland long-livedspeciesmadein the
lower Arctic stratosphere(18 - 20 km) between spring and
03 (ppmv)
autumnof 1997 were combinedwith a photochemicalbox model
to calculatetotal and net 03 destructionrates. The ratesare 10Figure 2. Total 03 destructionratesfrom Figure 1 plottedversus
20%/month in spring and midsummer, decreasing to near observed03 in ppmv. The datapointsare 100saverageswith the
5%/monthin early autumn. Productionof 03 plays a significant 1-daySE value indicatedby the color legend.
2608
FAHEY ET AL.: OZONE MEASUREMENTS IN THE ARCTIC STRATOSPHERE
reevaluationbased on laboratory studies, Geophys.Res. Lett., 26,
destruction
ratesincreasewith solarexposureandambient03
throughout
thedataset. A comparison
with transport
calculations 2387-2390, 1999.
showthat chemical03 destruction
predominates
overtransport Rosenlof,K., Estimatesof the seasonalcycleof massandozonetransport
at highnorthernlatitudes,J. Geophys.Res.,104, 26511-26523,1999.
effectsin springandthattransport
andchemical03 changes
are
more comparable in late summer/early autumn. Ozone Salawitch,R. S., et al., The diurnalvariationof hydrogen,nitrogen,and
chlorineradicals:Implicationsfor the heterogeneous
productionof
destructionrates and transport processesare both altitude
dependent. Hence, the resultspresentedhere may not be
generalized
to loweror higheraltitudes.Theseresultsprovidean
HNO 2, Geophys.Res.Lett., 21, 2551-2554, 1994.
Stimpfle,R., et al., The couplingof C 10NO2, C 1O, andNO2 in thelower
stratosphere
from in situobservations
usingthe NASA ER-2 aircraft,J.
observationally
basedreferencepointfor thecontinuedevaluation
Geophys.Res., 104, 26705-26714, 1999.
of observedspring/summer
03 changesand of atmospheric Swartz, W. H., et al., A sensitivitystudy of photolysisrate coefficients
models used to calculate present and future abundancesof
stratospheric
03.
Acknowledgements
Theauthors
aregratefulfor support
fromtheNASA
UpperAtmospheric
ResearchProgramand the Atmospheric
Effectsof
AviationProject,to J. A. Loganfor 0 3 data,to P. A. Newmanfor
backtrajectories,
andto S. G. Donnellyforinstrument
support.
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(ReceivedJanuary17, 2000; revisedMay 26, 2000; acceptedJune16,
2000)