Reactive nitrogen oxides and ozone above a taiga woodland
The Harvard community has made this article openly available.
Please share how this access benefits you. Your story matters.
Citation
Bakwin, Peter S., Daniel J. Jacob, Steven C. Wofsy, J. William
Munger, Bruce C. Daube, John D. Bradshaw, Scott T. Sandholm,
et al. 1994. “Reactive Nitrogen Oxides and Ozone Above a Taiga
Woodland.” Journal of Geophysical Research 99 (D1): 1927.
doi:10.1029/93jd02292.
Published Version
doi:10.1029/93JD02292
Accessed
June 15, 2017 3:00:36 PM EDT
Citable Link
http://nrs.harvard.edu/urn-3:HUL.InstRepos:14121871
Terms of Use
This article was downloaded from Harvard University's DASH
repository, and is made available under the terms and conditions
applicable to Other Posted Material, as set forth at
http://nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.termsof-use#LAA
(Article begins on next page)
JOURNAL OF GEOPHYSICAL
RESEARCH, VOL. 99, NO. D1, PAGES 1927-1936, JANUARY 20, 1994
Reactive nitrogen oxides and ozone above a taiga woodland
PeterS. Bakwin, DanielJ. Jacob,StevenC. Wofsy, J. WilliamMunger,
BruceC. Daube, JohnD. Bradshaw,
5 ScottT. Sandholm,
5 RobertW. Talbot,4
HanwantB. Singh,
5 GeraldL. Gregory,
6 andDonaldR. Blake7
Measurements
of reactive
nitrogen
oxides
(NOxandNOy)andozone(03) weremadein theplanetary
boundarylayer(PBL)abovea taigawoodland
in northern
Quebec,
Canada,duringJune-August,
1990,aspartof
NASAArticBoundary
LayerExpedition
(ABLE)3B. Levelsof nitrogen
oxides
and03 werestrongly
modulatedbythesynoptic
scalemeteorology
thatbrought
airfromvarious
source
regions
to thesite.Industrial
pollutionfromtheGreatLakesregionof theU.S. andCanadaappears
to bea majorsource
for periodicelevation
of
NOx,NOym•d03. WefindthatNO/NO2ratios
atthissiteatmidday
wereapproximately
50%those
expected
froma simplephotochenfical
steady
statebetween
NOxand03, in contrast
toourearlierresults
fromtheABLE
3A tundrasite. The differencebetweenthe taigaandttmdrasitesis likely due to muchlargeremissions
of
biogenichydrocarbons
(particularly
isoprene)
fromthetaigavegetation.Hydrocarbon
photooxidation
leadsto
relatively
rapidproduction
of peroxy
radicals,
whichconvert
NO toNO2,atthetaigasite.Ratios
of NOxto
NOy weretypically2-3 timeshigherin thePBLduringABLE3B thanduringABLE3A. Thisis probably
the
resultof highPANlevelsandsuppressed
formation
of HNO3 fromNO2 duetohighlevelsof biogenic
hydrocarbons at the ABLE
3B site.
1oINTRODUCTION
Recent investigationshave suggestedthat the abundanceof
We reportmeasurements
of 03 andnitrogenoxide(NO, NO2,
and total NOy) mixingratiosin the planetaryboundarylayer
(PBL) of the atmosphere
aboveandwithina taigawoodlandcano-
ozone
(03)isincreasing
inthetroposphere
and
that
the
rate
ofin- py,atalocation
remote
from
anthropogenic
sources.
Themeascrease
isespecially
rapid
athigh
northern
latitudes
insmnmer
urements
were
made
during
June-August,
1990,
aspart
ofNASA
[OltmansandKomhyr,
1986;Bojkov,
1988;FergusonandRosson,
Arctic
Boundary
Layer
Expedition
(ABLE)
3B.Observations
1992].
Ozone
regulates
theoxidizing
power
oftheatmosphere
were
made
ona31-m-high
tower
and
from
theNASA
Electra
airand is radiativelyactive,so that increasedozonelevelsmay have
an importantinfluenceon atmosphericchemistryand climate.
Ozoneis alsotoxic to vegetation,changesin 03 may directlyimpactthebiosphere.Tropospheric
03 levelsareregulatedprimarily
by photochemistry,
whichis sensitivelydependent
on nitrogenoxide (NOx = NO andNO2) mixingratios[Liu et al., 1987], surface
deposition,andby inputsfrom the stratosphere.
Industrialprocesses
andbiomassburningareprobablythe largest sourcesof NOx, with smaller contributionsfrom soil emissions
craft. Turbulentfluxesof 03 andtotalNOywerealsomeasured
at
the tower and will be reportedin a future publication(J. W.
Munger et al., •nanuscriptin preparation,1993, hereinafterreferred to s M93).
Section2 of this paperfocuseson the analyticalmethodsand
experimentaldesignusedat the tower; otherpapersin this issue
discussmethods used on board the aircraft [Talbot et al., this issue;Sandholmet al., this issue]. Section3 describesthe measure-
ments,and section4 examinesthe photochemical
steadystatefor
and stratospheric
inputs [Logan, 1983]. Photochemistry
in the
NO, NO2 and 03 (section4.1) and NO,JNOyratios(section4.2).
troposphere
convertsNO• to higheroxides,suchas HNO3 andor- Conclusions are summarized in section 5.
ganic nitrates. Many of thesespeciesare relativelyresistantto
furtherphotochemical
processing
and/ordepositionandsomay be
2. EXPERIMENT
transported
over large distances.The thermaland/orphotochemical decomposition
of someof the higheroxides,especiallyperoxOverflightsof the ABLE 3B groundsite by the NASA Electra
yacetylnitrate(PAN) andHNO3,retumsNO• to the troposphere. airplanewere madeon six days: Juliandays211 (mission10),
213 (11), 215 (12), 219 (14), 220 (15), and223 (17). On day 217
the Electra flew in the PBL so•newhat to the southest of Scheffer-
•Divisionof AppliedSciences,
HarvardUniversity,
Cambridge,
Massachusetts.
ville (mission 13). We will examine observationsof NO, and
2Now
atClimate
Monitoring
and
Diagnostics
Laboratory,
National
Oce-NOy,HNO3,PAN,03,C2H2
andC2Chobtained
in theboundary
anicand
Atmospheric
Administration,
Boulder,
Colorado.
layeraboardthe Electraduringtheseflights.The experimental
3School
of Atmospheric
Sciences,
Georgia
Institute
of Technology,
methods
usedto obtainthesedataaregivenby Talbotet al. [this
Atlanta, Georgiaø
issue]andSandholmet al. [this issue],andreferencestherein. The
4Complex
Systems
Research
Center,University
of New Hampshire,
arrayof NOv species
(NO,, PAN andHNO3)andothertracers(hydrocarbons,halocarbons,CO) measuredaboardthe Electra makes
5NASA AmesResearchCenter,Moffett Field, California.
6NASALangleyResearch
Center,Hampton,Virginia.
Paper number93JD02292.
the aircraftdata set particularlyusefulfor identifyinginfluences
on trace gas climatologies,such as industrial pollution and
biomassburning[see Wofsyet al., this issue]. We examineaircraft data obtained in the PBL in the region surroundingthe
Scheffervillegroundsite only; otherpapersin this issuefocuson
0148-0227/94/93 JD-02292505.00
data
7Department
of Chemistry,
University
of Califomia,Irvine.
Copyright1994by the AmericanGeophysical
Union.
1927
obtained
above
the
PBL
and
over
a broader
area
of
1928
BAKWIN
ETAL.:
NOx,NOyAND
03 ABOVE
ATAIGA
WOODLAND
northeastern
Canadaandthe easternUnitedStates(e.g.,Talbotet air at the inlet of the converterof =2 cm3 STP of a NationalInstial., Sandholm
et al., Wofsyet al.).
tutefor Standards
andTechnology(NIST) (Gaithersburg,
Mary-
Talbotet al. [thisissue]segregate
theaircraftdataobtained
in land)traceable
standard
gascontaining
4.42ppmvNO in N2.
variousaltitudeintervalswith air masstype,on thebasisof CO
Checkson the conversion
efficiencyfor NO2 wereperformed
mixingratios.We takea differentapproach
andaverage
thePBL twicedaily. For an efficiency
checktheNO standard
wasadded
datafor eachaircraftmission
to determine
thedominant
influencesto 50 cm3 STP of "zero"air containing
=2 ppmv03 in a 4 cm3
on thechemicalcomposition
of PBL air duringthetimeperiodof volumejust beforebeingintroduced
into the converter,
so that
eachflight.We founda highcorrelation
between
C2H2andCO in =99% of NO wasconverted
to NO2. The conversion
efficiency
biomassburningand industrialpollutionplumesand therefore remained
>95%for thefull observation
period.No measurements
focuson measurements
of C2H2asa tracerfor buming[seeWofsy of the conversionefficiencyfor higherN oxidesweredonein the
et al., this issue]. Mixing ratio data for CO are not availablefor field. In laboratorytestsusing HNO3 in humidified"zero" air,
muchof the flight time in the PBL becausethe CO instrumentwas efficientconversion
to NO wasobtainedat sampleflowratesup to
operatedin a fastresponse
modefor eddyflux measurements.
5000cm3 STP. Also,conversion
efficiencyfor NH3 in humidified
Thetowerdataprovidea nearlycontinuous
recordof NOx,NOy air (>20% relativehumidity(RH) at 23ø C) wasfoundto be negliand03 mixingratiosfor June27 to August17 (Juliandays178to giblein agreementwith resultsfrom otherlaboratories((3. Hltbler,
229), 1990,andincludenighttimeandperiodsof inclementweath- personalcommunication,1990).
er duringwhich the aircraftdid not fly. Furtherdetailsof the
Occasionallylocal pollution (mainly from the generator)was
tower measurements
are givenbelow.
sampledat the tower. During theseperiodsthe varianceof the
The towermeasurements
werecarriedoutin a blacksprucetai- NOymeasurements
wasgreatlyincreased
(coefficient
of variation
ga woodland13 km northwestof Schefferville,Provincede Que- > 2 for a 5-min period), so that such intervalswere easily
bec,Canada(54ø 50' N, 66ø 40' W), a townof approximatelyidentified and were removed from the data set.
3000 inhabitants.No othersignificant
habitations
existwithin200
A separatedetectorwas usedto measuremixingratiosof NO
km of the site. The woodlandcanopywas openwith ---600trees andNO2. Nitric oxidewasmeasured
by chemiluminescence
with
ha-l, andthemeancanopyheightwas5-6 m. A 31-m-high
tower 03, andNO2 wasmeasured
followingphotolysis
to NO [Bakwinet
(Rohn 25G) was erected and instrumentedfor chemical and mi- al., 1992]in a 165cm3 quartzcell at a sampleairflowrateof 800
crometeorological
measurements.
Chemicalanalyzers
and data
acquisition
andcontrol
computers
werelocated
in a tentabout20
m southeast
fromthebaseof thetower.Electrical
powerwasprovidedby a 12.5-kVAdieselgenerator
located
300m southeast
of
cm3 STP andpressure
of 300 torr. The reduced
pressure
in the
photolysis
cell minimized
theconversion
of NO to NO2by ambient03 [Ridleyet al., 1988;Bakwinet al., 1992]. Duringsamplingfromeachaltitude,
2 minwerespentin anNO modeand2
the tower.
•ninwerespentin anNO2 (photolysis)
mode.
The experimental
designwas similar to that describedby
To zero the NOx detector, a solenoid valve was used to introBakwinet al. [1992]. Mixingratiosandturbulent
fluxesof NOv ducea flow of 50 cm3 STP"zero"aircontaining
=100ppmvof 03
and03 weremeasured
at 29 and31 m height,respectively.Mix- to the sampleair just upstreamof the quartzcell, with no photoing ratiosof 03, NO andNO2 weremeasured
by samplingthrough lysis, so that NO was removed. At night,reactionwith ambient
0.635 cm OD. Teflon tubes with inlets fixed at 0.05, 0.85, 2.8, 6.2, 03 is expectedto completelyremoveNO, providinga checkon
9.5, 18.2, and30.8 m heighton or nearthe tower. The sampling the zeroingprocedure.The mean (standarddeviation)nighttime
sequencewas from highestto lowest,eachlocationwas sampled NO mixing ratio for 2.8 to 30.8 m was 0.2 (1.1, n=2124) pptv
for 4 min duringeachprofile. The NOx detectorwaszeroedfol- (parts per trillion by volume), with no significantdifference
lowingsamplingfrom the0.05-m tube.
betweensamplingheights(seeFigure3). Nitric oxidemixingraReactivenitrogenoxides(NOv) wereconvertedto NO by gold- tios at 0.05 m were elevated somewhat due to emission of NO
catalyzedreactionwith H9•at 300øC [Fahey et al., 1986] and from the surface(seebelow). Previously,we reportedan artifact
quantifiedusingchemiluminescence
with 03. The convertercon- of --1.7 pptv for our NO measurements
[Bakwinet al., 1992]. Insistedof a 90-cm-long,0.635 cm ID gold-plated(2.5 gm thick- troductionof a solenoidvalve to switchthe O3-1aden
zeroingair in
ness)coppertubeandwas locatedat the inlet endof the sampling andout of the sampleairstreamappearsto haveeliminatedthisartube. Calibration gasesand H9•were added to the sample air tifact(<0.5 pptv).
throughtwo 0.16-cm-OD stainlesssteeltubesthatintrudedseveral
Calibrationsfor NO andNO2 wereperformedevery3 hoursuscentimeters into the inlet of the converter tube. The converter
ing the methodsdescribedby Bakwin et al. [1992]. The NO
designminimizedinstrument
response
time to NOy speciesby (compressed
gas)andNO2 (permeationtube)calibrationstandards
minimizing contact of sample air with nonconvertingsurfaces were comparedin the field usinggold-catalyzedreactionwith H2
[Bakwinet al. 1992; M93]. The instrumentrespondedto a pulse to completelyconvertNO2 to NO. The NO standardwas coninputof HNO3 with a 90% risetimeunder2 s.
sideredthe primarystandardin the fieldandwasreferenced
before
After passingthroughthe converter,sampleair passedthrough andafter the field campaignto two NIST standards
maintainedin
=40 m of 0.635-cm-ODTeflontubingto theNO analyzer.Sample our laboratory. No significantchangewas observedin the workflow rate was900 cm3 min-• STP (cm3 STP). An instrument
zero ing sta•,dardbetweenthese two comparisons.Estimatesof the
was obtainedevery40 min by additionof 50 cm3 STP of "zero" precisionand accuracyof the NO and NO2 measurements
are
air containing=100 ppmv(partsper millionby volume)03 (gen- givenby Bakwinet al. [1992].
eratedusinga Hg vaporlamp) to the sampleair just downstream An ultraviolet(UV) photometer(Dasibi 1003-AH) was usedto
of the converter, so that NO was converted to NO9.. Calibrations determine03 mixingratios. The zerolevel of the photometer
was
for NO were carriedout every 3 hoursby additionto the sample determinedfrequentlyby passingthe sampleair througha screen
BAi(wn•
P.T
AL.:NOx,NO]/AND
03 A•ovp.AT•a•AWOODLAND
1929
impregnatedwith MnO2 and was foundto be stableto betterthan
+0.5 ppbv (partsper billion by volume)duringthe field experiment. To ensurea consistentcalibrationfor groundand aircraft
ozoneobservations,
the photometerwas comparedin the field to a
similarinstrumentcalibratedat NASA LangleyResearchCenter.
Ozone was also measuredcontinuously
at 30.8 m heightusinga
Bendix C2H4-chemiluminescence detector that was modified for
fastresponse,andthe datawere usedto computeturbulentfluxes
of 03 (M93).
Solar UV radiationwas measuredat the tower site usinga ra-
diometeridenticalto thoseflownon theElectra(EppleyLaboratory, Newport, Rhode Island). The radiometerwas mountedon a
pole at 6.1 m height,just abovethe topsof mostnearbytrees(5-6
m high). The radiometeroutputwas usedto computethe photo-
180
190
200
210
,IUI_IAN DAY,
i]20
230
1990
lysisrateforNO2,JNO
2,following
Madronich
[1987]:
1
JNO,
=1.35E(0.56
+0.03Z)
cosXo
+0.21
- 0.015Z
+2 (1)
'- :'I..: ,:'•i:' ,l,,I , ,' : [il,
whereE is theradiometer
signal(mW cm-2),Xo is thesolarzenith
angle,A is the albedofor UV radiation,andZ is the stationelevation (0.5 km abovesealevel). The UV albedowas obtainedfrom
extrapolationto the surfaceof the ratio of nadir to zenith looking
UV radiometerreadingstaken aboardthe Electra during lowaltitudeoverflightsof the groundsite (670-1300 m abovesealevel), givingA--O.03.For Xo < 70ø,equation(1) is expectedto yield
180
190
values
forJNO2
accurate
to-l-20%forbothclearandovercast
skies
[Madronich, 1987; Shetteret al., 1992].
Samples for hydrocarbonand halocarbonanalysiswere ob-
tainedat 10 and30 m heighton the toweron Juliandays220-224.
Methodsusedfor samplecollectionand analysiswere similar to
thoseusedfor aircraftsampling[Blakeet al., this issue]. We discusshere resultsfor acetylene(C2H2),perchloroethylene
(C2C14),
andisoprene.
200
210
,It II IAIq ()A¾,
',, I • , i ;!
I II•!:•i,111
220
230
1990
i. Ii"
, ,:! , I' ,!I.,,
.
3. OBSERVATIONS
3.1. MixingRatiosof NO,,, NOy , and0 3
Hourlymeanmixingratiosof NOx,NOy, and03 at 30 m above
thesurfacerangedfrom 15 to >150 pptv,<50 to >1500 pptv,and5
to49 ppbv,respectively
(Figure1). Themeanandmedian
diurnal
180
190
200
210
220
230
outIANDAY,1990
cycles
forNOx,
NOy,
and03at30mheight
areshown
inFigure
2. Fig.1.Time
series
of(a)NO•,(b)NOy,
and
(c)03mixing
ratios
at31m
MaximumNOyand03 levels,typicallyabout270 pptvand28 height
above
theground
ontheScheffervilletower.
ppbv, respectively,were observednear midday,coincidentwith
themaximumrateof verticalmixing. At mght,NOy and03 levels
in the surfacelayerweredepressed
dueto deposition
anddecou- Fitzjarrald and Moore [this issue] discussclimatological
pling from the atmosphere
above(M93). Mixing ratiosof NO, changes
thatoccurred
duringtheperiodof ourobservations.
They
were also somewhatlower at night than in the daytime. The reporta shiftin thesynoptic
regimearoundJulianday 197,froma
nighttime
lossrateforNO, (about1.3pptvh4 on average)
prob- coolperiodof frequent
precipitation
andwesterly
to northwesterly
ably reflectsnet deposition
to the surface(seebelow)as well as flow to a warmer,drierperiodcharacterized
by southwesterly
flow
reactionof NO2 with 03 to form NO3, whichmay be lostby depo- and generally deeper afternoonboundarylayers. A rerum to
sitionor via furtherreactions.
coolerweatherandwesterlyto northwesterly
flow occurredabout
Statistics
for NOx, NOv, and03 mixingratiosduringmidday
(1000-1600 easternstandardtime (EST)) for Juliandays 178 to
229, 1990,aregivenin Table 1. Probabilitydistributions
for NOx
andNOy weresomewhat
skeweddueto a relativelysmallnumber
of observations
with very high mixingratios: medianNO, and
NOv mixingratioswerelowerthanthemeans.The 03 datawere
morenearlynormallydistributed.
day 221. Thesechanges
in climatearereflectedin the NO, and
NOy mixing ratios(Figure 1); on average,higherdaytimelevels
were observedduringthe periodof generallysouthwesterly
flow
thanduringthe coolerperiods(Table 1). Ozonelevelswere not
significantly
correlated
with theclimatological
changes.
Figure3 showsthemeanverticaldistributions
(0.05to 31 m) of
NO, NO2, NOx, and 03 at eachheightfor nighttime(2000-0400
1930
BtocWIN
ETAL.:NOx,NOyAND0 3ABOVE
ATAIGA
WOODLAND
was emitted from the surface.
The emission rates for NO con-
sistentwith the observedgradientsare very small,lessthan 1 x
108moleculescm-2 s-l. Duringthe daytilne,emissions
of NO
from the soil appearto havebeenaboutbalancedby deposition
of
NO2 to theplantcanopyandground,resultingin little overallvertical gradientfor NO,, while at nightNO2 depositionslightlyex-
ceeded
NO emission.
Thenetfluxof NO, at night(FNo.)
canbe
estimatedas [Bakwin et al., 1992]
FNo,
=Fo,d[NO,l/dz
d[O3]/dz
..
(2)
-1
5
10
15
20
LOCAL IlMF
At night,Fo,averaged
about
5 x 10lømolecules
cm-2s-• (M93),
the NO, and 03 gradients(30.8-0.05 m) wereroughly5 pptv and
15 ppbv,respectively
(Figure3), yieldingFNo,= 1.7 x 107
moleculescm-2 s-l, or assuminga 100-m-deepnocturnalstable
layer,about0.3 pptv h-x, roughly20% of the observed
nighttime
loss rate for NO,.
3.2. PollutionInfluences
0
5
10
15
The time seriesof NO,, NOy, and 03 (Figure 1)clearly show
coherentvariations,=1 (e.g.,day 195) to 8 (e.g.,days193 to 201)
daysduration,correlatedwith surfacepressurechangesindicating
the influenceof synopticscaleair masscharacteristics.
Typically,
NOx,NOy, and03 wereenhanced
duringperiodsof fallingsurface
pressure,which tendedto be associated
with air originatingfrom
the southwestquadrant,accordingto 5-day back trajectoriesfor
surfaceair. Mixing ratios were relativelylow duringperiodsof
risingpressure,mostoften associated
with trajectoriesfrom theN
hemicircle,indicatingArctic air. Regionsto the southwestwere
apparently
significant
sources
of NOx,NOv, and03 at thesurface.
Mixing ratiosof NO, and NOy measuredat the towerappearto
have been somewhathigher than thosemeasuredsi[nultaneously
aboardthe aircraft. Direct comparison
is difficultsincethe aircraft
datarepresentmeanstaken over [nanykilometers,andbecauseof
the small numberof datapoints. The groundsite may havebeen
2O
lOCAl 11MF (l•o•lrs)
located in a zone of somewhat
elevated N oxide levels due to na-
tural processesor local anthropogenic
pollution. However, the
0
5
10
15
20
overall agreementof NOdNOy ratiosbetweenthe groundsite and
the airplane(seebelow and Figure7) indicatethat localpollution
lOCAl.. 11MF (hours)
wasprobablynot a significantproble•nat thegroundsite.
Fig. 2. Median(solidcurves)andmean(asterisks)
diurnalcyclesof (a)
Table2 showsmixingratiosof C2H2,C2Ch,NOy,and03 on the
NOx,(b)NOy,and(c)03 mixingratios
at31m height
above
theground
on tower and from the Electra (PBL only) for selectedflights. Acethe tower. Upperandlowerquartilesareshownby dottedcurves.
tyleneis emittedby bimnassandfossilfuel burningandhasa lifetimeof in thetroposphere
of 2-3 weeks,while C2Chis a purelyinEST) and midday(1000-1600EST). Ozonewas depletedat the dusthalproductwith a lifetimeof 12-14weeks. Mixing ratiosof
T ...........
1.....
i
F
--r-
---
lowestaltitudes
dueto surface
uptake,whichwasstrongest
during NOy and03 at the groundsitewerenearor belowtheirdaytime
thedaytime(M93). Mixing ratiosof NO weresomewhat
elevated background
valuesof 247 pptvand28 ppbv(asdefinedby mediat 0.05 m heightcompared
to otheraltitudes,
indicatingthatNO ansfor days178-196;seeTable1),respectively,
ondays215,219,
TABLE1. Statistics
forObserved
NOx,NOyand03 MixingRatios
Measured
at30m HeightontheSchefferville
Tower
Interval
NOx,pptv
NOy,pptv
03, ppbv
1990
178-229
Mean
s.d.
Median
LQ
UQ
n
Mean
s.d.
Median
LQ
UQ
n
Mean
s.d.
n
49
30
41
27
60
185
343
273
269
182
401
256
28
7
201
178-196
31
14
27
20
40
71
261
110
247
180
337
84
28
5
75
197-221
66
31
57
44
80
90
434
346
342
237
470
126
28
9
97
222-229
41
31
28
26
42
24
228
130
189
158
218
46
26
5
29
LQ denoteslowerquartile; s.d.denotesstandarddeviation;UQ denotesupperquartile;n, numberof observations.
BAKWIN
ETAL.:
NOx,NOyAND
0 3ABOVE
ATAIGA
WOODLAND
height (m)
height (m)
10
15
I
I
20
I
1931
20
25
25
30
0
5
10
15
I
i
I
I
I
I
5
10
15
20
25
I,
I
I
I
I
I
I
30
,
I
height (m)
height (m)
10
15
2O
25
3O
0
I
I
I
I
i
I
30
i .
_
.
•
0
_
I
.
Fig.3. Meanmixingratiosof NO,NO2,NOx,and03 at eachsampling
heightonthetowerfordaytime
(pluses,
1000to 1600
EST)andnighttime
(circles,
2000to 0400EST)(Julian
days178-228).Observations
lyingmorethan1.5timestheinterquartile
distance
fromtheupperandlowerquartiles
(seeFigure2) havebeenexcluded
fromthemeans.
220,222,223,and224,whichinclude
thetimeperiods
foraircraft polluted
PBLovermidlatitude
areas
during
mission
22,indicating
missions
12, 14, 15, and17oThesespecies
weresignificantly
thatthe air sampled
wasstrongly
influenced
by anthropogenic
abovebackground
levelson days211,213,and221,andalso sources.
Elevated
mixingratiosof NO•,NOy,andO3wereobC2Chmixingratiosexceeded
apparent
"background"
levelsof served
attheground
siteforabout
2.5dayspriortomission
10,in9.7-12.7pptv(rangeof datatakenonotherdays)on days211 dicating
thatthepollution
source
wasregional,
and5-daybacktra(mission
10)and221(noaircraft
flightovertheground
site).Dur- jectories
showthatairthatreached
thesiteduring
mission
10had
ingaircraft
mission
10,C2ChandC2H2
mixing
ratios
in thePBL passed
overtheGreatLakes
region
oftheUnited
States
andCanaoveroursitereached
levelscomparable
to thoseobserved
in the da (trajectories
arepresented
by Shipham
et al. [thisissue]),a
TABLE2a. MixingRatiosof C2H2,C2C14,
NOy,0 3,andNOxObtained
onthe
NASA ElectraAirplaneandontheSchefferville
TowerDuringOverflights
by theElectra
Aircraft
JDAY,
FLT
1990
211 a
213
215
217b
219
220
223
227 c
10
11
12
13
14
15
17
22
C2H2,
Tower
0 3,
NOx, NOy,
03,
NOx,
pptv
C2C14, NOy,
pptv
pptv
ppbv
pptv
pptv
ppbv
pptv
313
70
115
106
83
83
70
337
31.8
12.4
10.8
11.4
10.5
9.7
11.9
46.6
877
312
nd
209
133
202
112
3798
52
43
27
24
28
20
25
68
151
31
nd
33
31
38
31
728
1429
408
233
nd
267
256
188
49
40
23
nd
24
21
27
229
65
49
nd
55
69
39
Here nd denotes no data.
"Scheffervillespiralonly.
bFlightsoutheast
of Schefferville.
CTransitflight (midlatitudes).
1932
BaxwIN
ETnt,.:NOx,NOyAND
0 3ABovE
^ TAm^WOODLAND
TABLE 2b. TowerDatafor IntervalsWhenGrabSamples
Were Takenfor Hydrocarbon/Halocarbon
Analysis
JDAY,
1990
C2H2,
pptv
C2C14, NOy,
pptv
pptv
03,
ppbv
supportedby our data from the ABLE 3A tundrasite [Bakwinet
al., 1992],whereNOxmixingratiosweretypically12•.4pptvand
wereapparently
little affectedby recentemissions.The frequency
distribution
for NOx in the modelagreeswell with the observa-
NOx,
pptv
tionsat thehighpercentiles,
andthe modeltime series(not shown)
showsepisodes
of elevatedNO• and03 of similarmagnitude
and
duration
to
those
observed
(Figure
1),
indicating
that
the
transport
222
72
11.7
125
24
28
of NO• (or NO• precursors
suchas PAN) from industrialsources
223
67
12.4
172
27
36
is realisticallysimulatedfor thissite.
224
65
12.7
235
29
nd
The modelpredictslargenorthwardtransportof NO• and03 in
thePBL at 54øN overeasternCanadaduringJulyandnegligible
highly industrializedarea. The enhancements
of C2C14and C2H2 transportof NO• and 03 above the PBL. Examinationof the
at the toweron day 221 weremuchsmaller,indicatingthatanthro- model time series for NOx and 03 over the easternUnited States
pogenicpollution,thoughpresent,wasmoredilutethanduringthe andCanadarevealsthatthesespeciesaretransported
to Schefferepisodeof days209-211. Theseresultsindicatethatdistantindus- ville episodically
duringtheapproach
of low-pressure
systems,
in
220
99
10.2
276
21
66
221
125
16.3
334
38
67
trialsources
hada pronounced
influence
onNOx,NOv,and03 lev- harmonywith our observations
of generallyelevatedNO•, NOv,
els observedat the groundsite. The highermixingratiosof 03 in and03 levelsduringperiodsof fallingpressure.Theseperiodsare
thepollutedair massesmostlikely reflectnetphotochemical
pro- characterized
by subsidence
over the studyarea, which actsto
duction(or suppressed
destruction)in the presenceof elevated confine industrialpollution within the PBL [Fitzjarrald and
Moore, thisissue].
Enhancements
of C2H2(and otherhydrocarbons)
observedon
days217 (mission13) and220 were not associated
with increased
4. INFLUENCE
OFPHOTOL•IEMISTRY
ONNO• ANDRADICALS
C2C14or NOv and hencewere mostlikely due to borealbiomass
SteadyStatefor NO•, and 0 3
fires. Detailed investigationsof biomassburningand industrial 4.1. Photochemical
pollutionplumesobservedfrom the Electraover Alaska(ABLE
Duringthedaytime,NO, NO2,and03 arecycledon a timescale
3A [Wofsyet al., 1992]) andnortheastern
Canada(ABLE 3B [Talbotet al., thisissue;Wofsyet al., thisissue])showthatNOv/CO of minutesby thereactions
and NOv/hydrocarbon
emissionratiosare low in biomassfires
comparedto industrialemissions.
NO + 03 -->NO2 + 02
(3)
Jacob et al. [1993] have useda chemicaltracermodel (CTM),
with transportfieldsfrom the GoddardInstitutefor SpaceStudies
global circulation model [Hanson et al., 1983], and with
NO2 + hv -• NO + O
(4)
parameterized
photochemistry
[Spivakovsky
et al., 1990],to simulate mixing ratios of 03 and its precursorsover North America.
The modelproducesmixingratiosof 03, NO•, andCO in general
0+02+ M --> 03+ M
(5)
agreementwith observations
takenat a numberof sitesthroughout
the United States,and successfully
simulates
episodesof high03
in the easternUnitedStatesthatoccurduringperiodsof stagnant wherehv represents
photonswith wavelengths
<420 nm. If isolatmeteorology
in summer(seeJacobet al. [ 1993]for details).
ed from strongsources
or sinksfor NO, or 03, thesereactions
may
Table3 comparesthefrequencydistributions
for NO• generated reacha photochemical
steadystatesuchthat
from the modelfor 1430 EST duringJune-August
in the (4ø x 5ø)
grid cell containingthe Scheffervilletower,with thoseobservedat
the tower (1000-1600 EST). We comparethe modelresultsand
observations
for daytimeonly becauseat nightthe observedmixing ratiosare somewhatdepletedbelowthe shallowinversionby
surfacedeposition
andchemistry(seeFigure2). The observed
NO•mixing
ratios
are10-24
pptvhigher
thanthemodel
foreach
percentile.
Sincetheonlysources
forNOxin themodelareindustrial, theseresultsindicatethat "background"
NOx levelsat the
Schefferville
site(i.e.,air masses
thatareunaffected
by recent
NO• inputs)arein therangeof 10-24pptv. Thisinterpretation
is
TABLE 3. ObservedandSimulated(CTM) NOx (pptv)
FrequencyDistributionsat the ScheffervilleSite
Percentile
Observations
0
Model
I
I
I
5
10
15
20
t_OCALlIME (hours)
5
18
17
24
2
2
50
42
18
from measurements
of NO, NO2, 03, temperature
(k), andtheoutputof a
UVradiometer
(J•4o:),
plotted
against
timeofday.Hourly
means
(+1s.d.)
83
72
58
95
120
110
CTM, chemical tracer model.
Fig.4. Valueof P = JNo:[NO2]/k[NO][O3],
whichhasbeencomputed
areshownby thedottedcurves.Pointswith P < -1 or P > 13 havebeenexcludedbasedon examination
of theprobabilitydistribution
functionfor the
data(52 outof 1799points).
BAKWIN
ETAL.:NOx,NOyAND0 3 ABOVE
ATAm^WOODLAND
p=k[NOl[O31
JNo:[NO2]
1933
(6)
wherek is the rate constantfor (3) andis a functiononly of temperature. At steadystate,P shouldexceedunity if reactionsother
than(3)convert
NO toNO2.WithJNo,
computed
fromtheoutput
of theUV radiometer(equation(1)), all of theparameters
required
to computeP were measuredat thissite.
The valueof P, computedfor NOx and03 measurements
taken
abovethe treetopsat 6.2, 9.5, 18.2, and30.8 m, is plottedagainst
time of day in Figure4. We find that P is not stronglydependent
onsunangleduringmostof thedaytime
noronJNo,
(notshown).
Duringtypicalmidday
conditions,
JNo,
= 0.0055s-• andP = 2.9
0.0
0.002
0.004
0.006
0.008
JNo:(S1)
(mediansfor 1200-1400 EST). These resultsindicate that reac-
tions
ofNOwithcompounds
other
than
03playanimportant
role Fig.
6. Computed
peroxy
radical
mixing
ratios
(equation
(7))required
to
explainobservedNO/NO2 ratios,plottedagainstthe NO2 photolysisrate,
in determiningthe ratio of NO2 to NO at this site, in agreement
with
theother
measurements
inthe
rural
and
remote
troposphere
JNO
2.The
output
ofanEppley
UVradiometer
has
been
used
tocompute
[Ritter
etal.,1979;
Kelly
etal.,1980;
Parrish
etal.,1986;
RidleyJN%
following
Madronich
[1987],
asoutlined
inthetext.
The
slope
ofthe
etal., 1992].
regression
lineis26240
pptv*s,
R2=0.37.
Reactionof NO with peroxyradicals(HO2 and RO2, whereR
represents
anorganic
group)
wouldleadto a valueof P > 1. The whichwerealsoobtained
ata remote
(lowNOx)site.Thestrong
peroxy
radicalabundance
required
toproduce
theobserved
depar-relationship
between
computed
peroxy
radical
levelsandUV radi-
turefromthesimple
photochemical
steady
state
of(3)-(5)
isgivenation
(JNo,)
isexpected,
since
peroxy
radical
production
isphoto-
approximately
by
chemically
controlled.
Ourfindings
fortheABLE
3Bforest
site
k
[HO•.]+ [RO•.]= [O3](P-1)
differ
significantly
from
those
for
the
ABLE
3A
tundra
site
where
(7) biogenichydrocarbon
emissions
andperoxyradicalproduction
rateswererelativelyslow [Jacobet al., 1992].
where
k'isthe
rate
constant
forthe
reaction
ofNOwith
HO•.
(note
4.2.NO•,/NOy
Ratios
that the rate constantsfor reaction of NO with HO2, CH302, and
C2H502
are
similar
[Demore
etal.,1990]).
The
computed
peroxyRatios
ofNOx
toNOy
obtained
onthetower
and
aboard
the
radical
mixing
ratios
areshown
inFigure
5. Atmidday
wefindElectra
when
flying
inthePBL
over
northeast
Canada
show
very
that
HO2+RO2
=71(median,
quartiles
=28and
153)
pptv.
About
similar
distributions
(Figure
7).The
ratios
areremarkablely
con-
half of the variancein the computedperoxyradicalmixingratios
stantovertherangeof NOymixingratiossampledandthemeans
is explained
by a linearrelationship
withJN%(Figure6), andthe (+ s.d.) for the tower (0.20-!-0.10,n=808) and aircraft (0.19+0.09,
relationship
between
HO2+RO2
andJso:
isverysimilar
tothatre- n=268)
areverysimilar.
These
lowratios
indicate
thatfresh
inportedbyParrishet al. [1986]at NiwotRidge,Colorado,for summetperiodswithNO• mixingratiosbetween250 and1000pptv.
However,NOx levelsat our site are muchlowerthat at Niwot
Ridge,rarelyexceeding
150pptv,andwe findno significant
relationshipbetweenperoxyradicalsandNO• at our site. The latter
putsof NO• hadnotoccurred
recentlyrelativeto theNO• lifetime
(about1 day). TheNOx/NOyratiosappearto increase
somewhat
at thelowestNOyabundances,
butthismaybe duein partto randommeasurement
errorsat lowNO• andNOy. Dataobtained
during ABLE 3A over the tundraof SW Alaskaalsoshowedlower
resultis in agreement
withtheobservations
of Ridleyetal. [1992], NO,JNOy
ratios,0.08(+_0.02,
alsoapparently
uncorrelated
withthe
mixingratio of NOy [Bakwinet al., 1992], indicatingimportant
differencesbetweenprocesses
that controlNO• mixing ratiosin
thesetwo regions.
5. DIscussioN
The low mixing ratiosof NO•, NOv, and 03 and the low
NOx/NOyratiosobserved
confirmthatthiswoodland
siteis indeed
remote from direct industrialinfluence. During periodswhen
"background"
(Arctic) air was sampled,NOv mixingratios(generally 180-340pptv) wereamongthe lowestseenat anycontinental location, and were similar to levels we observed at a tundra site
LOCAL TIME (hours)
in southwest
AlaskaduringABLE 3A [Bakwinet al., 1992]. NO•
mixingratioswerealsolow in "background"
(Arctic)air, typically
2040 pptv,but were2-3 timeshigherthanat the ABLE 3A tundra
site. Background
NO• levelsat thetaigasitewereneartheexpected crossoverpointfor net production/destruction
of 03 by photo-
Fig.5. Computed
(equation
(7))peroxy
radical
mixing
ratios
0tO2+RO2)chemistry.
required
to explain
observed
NO/NO2
ratios,
plotted
against
timeof day. Elevatedmixingratiosof NO•, NOv,and03 wereobserved
epHourlymeans
(:!:1s.d.)areshown
bythedotted
curves.
isodicallyat boththe tundra(ABLE 3A [Bakwinet al., 1992]) and
1934
BAKWIN
ETAL.:
NOx,NOyAND0 3 ABOVE
ATAIGA
WOODLAND
al. [1993] show that essentiallyall of the transportof industrial
pollutionoccursin thePBL.
,
***%
......
I
1
200
400
[
600
I
I
800
1000
T .....
1200
[
1400
[I'•Oy
]
In theCTM, roughly5% (0.9 x 109g N d-1) of theNOxemitted
by industrialsourcesin the UnitedStatesandCanadais transported to the Arctic northwardof 60øN duringsummer. This is approximatelyequivalentto eachof the sourcesof NO• to the Arctic
troposphere
from biomassburning[Jacobet al., 1992; Wofsyet
al., this issue] and from the stratosphere
[Jacob et al., 1992].
North Americansourcessupplyapproximately
35% of the global
sourceof NO• fromindustrialprocesses,
anda largeportionof the
remainderis emittedat midlatitudesin EuropeandAsia. If a similar fraction(5%) of emissions
from all industrialsources
is export-
edto or emittedin theArctic,thetotalindustrial
sourceof NOyto
theArcticin summerwouldbe about2.6 x 109g N d-1. Examination of statistics for NO• emission from industrial sources com-
piled by Harneedand Dignon [1988] indicatesthat the 5% estimate may be reasonablefor Europeand Asia, where industrial
centers reside farther north than in North America.
7
Measuredwet and dry depositionof NOy at our site totaled
about35 g N ha-] month
-] (M93), verysimilarto deposition
rates
at theABLE 3A tundrasiteat 62øN (36 g N ha-1 month-1 [Bakwin
et al., 1992; Talbot et al., 1992]). If we assumethat deposition
7
74
•l•7
37 5
rates measuredat thesetwo sites are representativeof the world
northwardof 60øN(3.4 x 109 ha) in summer,we wouldcalculatea
oo
oo
ø ø•g'ø%o• o
o
T
0
....
1 .......
200
T
400
I
600
I
800
-T .....
1000
T......
1200
l' -
1400
[N%] (pptv)
depositionflux of 4.0 x 109 g N d-1, giving a roughbudgetfor
NOy for the Arctictroposphere
in summer.Sourcesfromindustrial pollution(2.6 x 109 g N dq) wouldaccountfor =50%of thetotal, with the balancefrom biomassburning(0.9) and the stratosphericinput(0.9), approximately
balancedby wet anddry deposition(4.0). Mixingratiosof NOyobserved
in the Arcticaremuch
Fig.7. NOx/NOy
plottedagainst
NOyfordataobtained
(a) attheScheffer- higher in winter than in summerdue to increasedtransportfrom
ville tower,and(b) in the planetaryboundarylayer (PBL) by instruments midlatitudesandreducedlossrates[Honrathand Jaffe, 1992].
aboardthe NASA Electraairplane. Aircraftdataare shownby numbers
Levels of NO• in the PBL were low under backgroundcondiwith 0-7 indicatingdatafrommissions10-17,respectively
(excludingmistions(20-40 pptv), leadingto slowratesof netphotochemical
prosion 16). No data were obtainedin the PBL duringmission 12 due to
duction
of
03,
about
0.8
ppbv
day
-•
(S.
M.
Fan
et
al.,
manuscript
equipmentfailure.
taiga (ABLE 3B) sites associatedwith pollutionfrom industrial
and/orbiomass-burning
sources.Pollutioneventsare especially
evidentin the ABLE 3B data set (Figure 1). It is difficultor impossibleto separatethe effectsof industrialprocesses
from those
of biomass
fireson thebasisof theNOx,NOy,and03 dataalone,
in preparation,1993, hereinafterreferredto as F93). Lossof 03
by depositionto the surfacewas somewhatlarger,about1.6 ppbv
d-• (M93). Intervalswith NOx levelsin the range50-150 pptv,
persistingfor severaldays,were observedat this site;the elevated
NO• was contributedat leastin part by industrialpollutionfrom
theGreatLakesregionof the UnitedStatesandCanada.Biomass
fires may also have played a role but cannotbe unambiguously
distinguished.Periodsof elevatedNO• were associatedwith
elevated03 (Figure 1), and the CTM results[Jacobet al., 1993]
howeverthe hydrocarbonand halocarbondata (Table 2) clearly
indicatethat industrialpollutionis a sourcefor tracegasesmeasured at the taiga woodland site. Future studiesshouldinclude indicate that the 03 enhancements could result from enhanced
measurements
of "fingerprint"
compounds
suchas C2Ch simul- photochemical
production
(or suppressed
loss)withintheindustrial pollution plumes. Potential 03 productionrates are much
taneouswith nitrogenoxideand03 measurements.
Our finding of an importantindustrialpollution influenceis greaterat this site thanat the ABLE 3A tundrasitedueto higher
somewhat counter to that of Talbot et al. [this issue], who con- mixing ratios of large amountsof biogenichydrocarbons
at this
cludedthat biomassburningwas the main sourceof elevatedN(')• site.
NO• levelsduringa 3-weekperiodof generallyfair weatherand
andNOy mixingratiossampledaboardthe Electra.This differflow (Juliandays 197-221,Table 1) wereon averenceis likely due to differencesin the datasetsaddressed
in the southwesterly
two papers. In particular, Talbot et al. excludedfrom their age twice thoseobservedduring coolerperiodsof westerlyand
flow (178-196and222-229). HigherNOxis expectanalysisthe industrialpollutionepisodeencountered
in the PBL northwesterly
duringmission10 (as well as industrialpollutionencountered
in edto leadto greaternetproduction
of 03; however,03 levelswere
the marineboundarylayer off northeastCanadaduringmission not significantlydifferent betweenthese two broad intervals.
16), andtheyfocusedlargelyon dataabovethe PBL. The tower
data clearly show that the episodeon days 209-211 was not
unique,reflectinga patternthat repeatedseveraltimes. The
meteorological
conditions
leadingto transport
of industrialpollution from the GreatLakesregion(i.e., highpressure
overmuchof
northeast
Canada)are associated
with subsidence,
andresultsfroin
the three-dimensional
chemicaltracermodel(CTM) of Jacobet
Southwesterly
flow is generallyassociated
with subsidence,
with
stronglycappedPBLs[FitzjarraldandMoore,thisissue],sothat
the supplyof 03 fromaloft may be reduced.Also,sincetheloss
of 03 by surfacedeposition
is abouttwiceasfastasphotochemical
production,our result is perhapsnot surprising.Further,the
periodsof strongestsouthwesterly
flow and highestlevelsof industhalpollution,suchas the episodesof days209-211 andday
BAKWIN
ETAL.:
NOx,NOyAND
0 3ABOVE
n TAIGA
WOODLAND
1935
221, we observed
a clearenhancement
of 03 overbackground
lev- "missing"duringdownslopeperiods[Atlaset al., 1992], at our
els (Figure1). The overallimpactof industrialpollutionon re- ABLE 3A siteabouthalfof theobserved
NOyis "missing"
andapgional03 levelsis moderated
by therapidlossof NOxwithinthe pearsto consist
of fairlystablespecies
thatareresistant
to deposiPBLandbydeposition
of 03 to thesurface.
tion[Bakwinet al., 1992]. At thePennsylvania
site[Buhret al.,
We find thatNO/NO2ratiosobserved
at the taigasiteare not 1990] andour ABLE 3B taigasite [Sandholm
et al., thisissue],
well described
by a simplephotochemical
steadystateinvolving nearlyall of NOy is accounted
for by measuredspecies.This
only NOx and03, indicatingthatotheroxidantsare importantin comparison
may indicatethat the "missing"
NOy speciesdo not
converting
NO to NO2. Peroxyradicalsproduced
from isoprene playa majorrolein thebudgets
of NO• at thesesites.
oxidationare likely the major causeof low the NO/NO2 ratios
(F93). Oxidationof NO by 03 alone is sufficientto explain Acknowledgments.
Thisworkwassupportedby
NASAgrantNAG1-55
NO/NO2ratioswe observed
at the tundrasiteduringABLE 3A to Harvard
University
andby theAlexander
HostFoundation.
We are
[Bakwin,1989],consistent
withestimates
of low peroxyradical grateful
toM. Shipham
foruseful
discussions
concerning
themeteorologi-
mixingratiosandproduction
ratesfromhydrocarbon
precursors
calcontext
forthese
measurements,
toJ.Barrick
forloan
ofthecalibrated
[Jacob
etal.,1992].
UVradiometer,
andtoS.Fanforhelpful
discussions
concerning
photo-
Though
NOylevels
were
similar
in"background"
airatthetun- chemistry
attheABLE
3Bsite.
Wealso
thank
D.Barr
and
A.McNally
of
dra(ABLE
3A)andtaiga
(ABLE
3B)sites,
NOx/NOy
ratios
weretheMcGill
Subarctic
Research
Station,
J.Drewry
ofNASA
Langley
2-3times
higher
atthetaiga
site.Further,
PANi•qOy
ratios
wereResearch
Center,
and
D.Fitzjarrald
and
K.Moore
ofthe
State
University
of New York (Albany)for theireffortsin the field.
muchhigherin the PBL over the taigasite(0.2-0.5 [Sandholm
et
al., this issue])than over the tundrasite (--0.05 [Sandholmet al.,
1992]).Theseresults
likelyreflect
differences
in theNO•budgets
at these locations.
REFERENCES
At the tundra site the balance between PAN
decomposition
andHNO3formation
appears
toregulate
NO•lev- Atlas,
E.L.,B.A.Ridley,
G. Hitbler,
J.G.Walega,
M.A.Carroll,
D.D.
els[Jacob
etal.,1992].Thisbalance
must
alsoholdforthetaiga Montzka,
B.J.
Huebert,
R.B.Norton,
F.E.Grahek,
and
S.Schauffer,
Par-
site,
since
theessentially
alloftheNOy
measured
inthePBLisac- titioning
and
budget
ofNOy
species
during
theMauna
Loa
Observatory
counted
forbyobserved
species
(i.e.,NO•,PAN,HNO3,
and PhotochemistryExperiment,
J.Geophys.
Res.,97,10,449-10,162,
1992.
NOs-)
[Sandholm
etal.,thisissue].
A major
difference
between
Bakwin,
P.S.,
Reactive
nitrogen
oxides
inremote
areas:
Atmospheric
con-
these
twosites
istherelatively
high
isoprene
emission
rates
from centrations
and
atmosphere/biosphere
exchange,
Ph.D.
thesis,
Div.of
Appl.Sci.,HarvardUniv.,Cambridge,
Mass.,1989.
the taiga vegetation(isopreneemissionsfrom the tundra were
Baitwin,
P.S.,S.C.Wofsy,andS.M.Fan,Measurements
of NOxandNOy
essentiallyzero). Trainer et al. [1991] found that increasing
concentrations
and fluxes over Arctic tundra,J. Geophys.Res., 97,
isopreneemissions
in theirphotochemical
modelof theruralPBL
16,545-16,557, 1992.
causeda shiftof NOx oxidationfrom HNO3 to organicnitrates,inBlake,D. R., T.W. Smith,Jr.,T.-Y. Chen,W. J. Whipple,andF.S. Rowcluding PAN. The reason for this is threefold: (1) increased land,Effectsof biomassbuntingon summertime
nonmethane
hydrocarisopreneleadsto higherratesof peroxyacetyl(PA) radicalprobonsin the Canadianwetlands,
J. Geophys.
Res.,thisissue.
duction during the daytime, suppressingthe decompositionof Bojkov,R.D., Ozonechanges
at thesurface
andin thefreetroposphere,
in
PAN; (2) peroxyradicalsfrom isopreneoxidationconvertNO to
TroposphericOzone,edited by I.S.A. Isaksen,pp. 83-96, D. Reidel,
NO2, leadingto an increasein theNO2/NO ratio andfurtherlimitNorwell, Mass., 1988.
ingPAN decomposition;
and(3) isoprene
anditsoxidation
pro- Buhr,
M.P.,D.D.Parrish,
R.B.Norton,
F.C.Fehsenfeld,
R.E.Sievers,
and
ductscompetedirectlywith NO2 for reactionwith OH, so that
HNO3 formationis reducedas isoprenelevelsare increased.The
J.M.Roberts,
Contribution
of organic
nitrates
tothetotalreactive
nitrogenbudget
ata ruraleastern
U.S.site,J. Geophys.
Res.,95,9809-9816,
resultsof Trainer et al. [1991] are in harmonywith our comparis- !990.
on of the ABLE tundraand taiga sites;the local biota appearto Carroll,M.A., B.A. Ridley,D.D. Montzka,G. Hitbler,J.G.Walega,R.B.
exerta stronginfluence
onNO2/NOandPAN/NOyratios.These Norton,
B.J.Huebert,
andF.E.Grahek,
Measurements
of nitricoxide
ideasarebeingexplored
furtherthrough
photochemical
modeling andnitrogen
dioxide
during
theMauna
LoaObservatory
Photochemistry
of theABLE3B dataset(F93).
Experiment,
J.Geophys.
Res.,
97,10,361-10,374,
1992.
Ratios
ofNO•toNOymeasured
ataruralsiteinPennsylvania
Demore,
WoB.,
S.P.Sander,
D.M.Golden,
M.J.Molina,
R.F.Hampson,
during
thedaytime
in summer
werealsoabout
0.2,though
NO,• M.J.Kurylo,
CoJ.
Howard,
andA.R.Ravishankara,
Chemical
kinetics
andNOv mixingratiosweremuchhigherthanat ourtaigasitedue
andphotochemical
datafor usein stratospheric
modeling,JPL Pub.901, Calif. Inst. of Technol., Pasadena,Calif.,•1990o
to theproximityto emissions
[Buhret al., 1990]. At nightat the
Fahey,D.W., C.S. Eubank,G. Hitbler,andF.C. Fehsenfeld,
Evaluationof
Pennsylvania
site,NOdNOyratiosincreased
to 0.6-0.8 as NO•
emissionscontinuedwith reducedrates of conversionto higher
oxides [Trainer et al., 1991]. At our site no such nocturnalin-
a catalyticreductiontechniquefor the measurement
of total reactive
odd-nitrogen
(NOv)in the atmosphere,
J. Atmos.Chem.,3, 435-468,
1986.
creasein NOx/NOywasobserved.Theseresultsindicatethatthe Ferguson,E.E., andR.M. Rosson(Eds.),Climatemonitoringanddiagnosapproachto equilibriumbetweenNOx andNOv is achievedin a
ticslaboratory,Suture.Rep.20, 1991, Natl. OceanicandAtmos.Admin.,
fewhours
under
conditions
of vigorous
photochemical
activity Boulder,
Colo.,
1992.
andmaybemaintained
foratleast
several
days,
even
asNOyis Fitzjarrald,
D.R.,
and
K.E.Moore,
Growing
season
boundary
layer
climate
depleted
bydilution
anddeposition.
At sites
where
reactive
hy- andsurface
exchanges
inthenorthern
subarctic
woodland,
J.Geophys.
drocarbons
arenotabundant,
suchastheMaunaLoaObservatoryRes.,
thisissue.
(MLO) [Carrollet al., 1992]andour ABLE 3A tundrasite[ Hanson,
J.,G.Russell,
D.Rind,
P.Stone,
A.Lacis,
S.Lebedeff,
R.Ruedy,
Babeinet al., 1992],equilibrium
NOx/NOyratiosaresomewhat andL. Travis,
Efficient
three-dimensional
global
models
forclimate
stulower, typicallyaround0.1.
dies:ModelsI andII, Mon.Weather
Rev.,111,609-662,1983e
The differencemay be explainedin part by the by the relative Hameed,
S., andJ. Dignon,Changes
in thegeographical
distributions
of
abundance of
"missing" NOy
species (i.e.,
[NOy]-
([NO•]+[HNO3]+[NO•-]+[PAN])).At MLO, about25% of NOy is
global
emissions
of NOx andSOx fromfossilfuelcombustion
between
1966and1980,Atmos.
Environ.,22,441-449,
1988.
1936
BAKWIN
ETAL.:NOx,NOyAND0 3 ABOVE
ATAIGA
WOODLAND
poundsin the troposphere
overAlaskaandCanada:ABLE 3B, J. Geophys.Res.,thisissue.
Shetter,R.E., A.H. McDaniel, C.A. Cantrell, S. Madronich,and J.G. Cal20,630, 1992o
vert,Actinometer
andEppleyradiometer
measurements
of theNO2phoJacob,D.J.,et al., Summertime
photochemistry
of thetroposphere
at high
tolysisratecoefficientduringthe MaunaLoa Observatory
Photochemisnorthemlatitudes,
J. Geophys.
Res.,97, 16,421-16,432,1992.
Jacob,D.J., et al., Climatologicalsimulations
of summertime
ozoneover
try Experiment,
J. Geophys.
Res.,97, 10,349-10,360,1992.
Shipham,M.C., A.S. Bachmeier,D.R. Cahoon,Jr., G.L. Gregory,B.E.
NorthAmerica,J. Geophys.
Res.,98, 14,797-14,816,
1993.
Anderson,
andE.V. Browell,Meteorological
interpretation
of theArctic
Kelly,T.J.,D.H. Stedman,
J.A.Ritter,andR.B. Harvey,Measurements
of
BoundaryLayer Expedition(ABLE) 3B flight series,J. Geophys.Res.,
oxidesof nitrogenand nitric acid in dean air, J. Geophys.
Res.,85,
Honrath,R.E., andD.A. Jaffe,The seasonal
cycleof nitrogenoxidesin the
arctictroposphere
at Barrow,Alaska,J. Geophys.
Res.,97, 20,615-
7417-7425, 1980.
this issue.
Liu, S.C., M. Trainer,F.C. Fehsenfeld,
D.D. Parrish,E.J.Williams,D.W.
Fahey,G. Hlibler,andP.C. Murphy,Ozoneproduction
in the ruraltro-
Spivakovsky,
C.M., S.C.Wofsy,andM.J. Prather,A numerical
methodfor
parameterizafion
of atmospheric
chemistry:computation
of tropospheric
posphere
andthe implications
for regionalandglobalozonedistribu- OH, J. Geophys.Res.,95, 18,433-18,439,1990.
Talbot,R.W., A.S. Vijgen,andR.C. Harriss,Solublespecies
in the sumtions,J. Geophys.
Res.,92, 4192-4207,1987.
Acidic gases,aerosols,
and precipitation,
J.
Logan,J.A., Nitrogenoxidesin the troposphere:
Globaland regional mer Arctic troposphere:
Geophys.
Res.,97, 16,531-16,544,1992.
budgets,
J. Geophys.
Res.,88, 10785-10807,1983.
Logan,J.A., M.J. Prather,S.C. Wofsy,andM.B. McElroy,TroposphericTalbot, R.W., et al., Summertime distributionsand relations of reactive
chemistry:
A globalperspective,
J. Geophys.
Res.,80,7210-7254,1981.
Madronich,
S., Intercomparison
of NO2 photodissociation
and U.V. ra-
oddnitrogen
species
andNOyin thetroposphere
overCanada,
J. Geophys.Res.,thisissue.
Trainer,M., et al., Observations
andmodelingof thereactivenitrogenpho-
diometermeasurements,
Atmos.Environ.,21,569-578, 1987.
tochemistry
at a ruralsite,J. Geophys.
Res.,96, 3045-3063,1991.
Oltmans,S.J., and W.D. Komhyr,Surfaceozonedistributions
andvariationsfrom 1973-1984measurements
at the NOAA geophysical
monitor- Wofsy, S.C., et al., Atmosphericchemistryin the Arctic and subarctic:
Influenceof naturalfires,industrialemissions,
and stratospheric
inputs,
ing for climaticchangebaselineobservations,
J. Geophys.
Res., 91,
J. Geophys.
Res.,97, 16,731-16,746,1992.
5229-5236, 1986.
Parrish,D.D., M. Trainer,E.J.Williams,D.W. Fahey,G. Hlibler,C.S. Eu- Wofsy,S.C., S.M. Fan,D.R. Blake,J.D. Bradshaw,S.T. Sandholm,H.B.
andR.C. Hatriss,Factors
influencing
of atmospherbank,S.C. Liu, P.C. Murphy,D.L. Albritton,and F.C. Fehsenfeld, Singh,G.W. Sachse,
over subarcticNorth Americaduringsummer,J. GeoMeasurements
of the NOx - 03 photostationary
stateat Niwot Ridge, ic composition
phys.Res.,thisissue.
Colorado,
J. Geophys.
Res.,91, 5361-5370,1986.
Ridley,B.A., M.A. Carroll,G.L. Gregory,
andG.W.Sachse,
NO andNO2
in thetroposphere:
Technique
andmeasurements
in regions
of a folded
P.S. Bakwin, Climate Monitoringand DiagnosticLaboratory,NOAA,
tropopause,
J. Geophys.
Res.,93, 15,813-15,830,
1988.
325 Broadway,Boulder,CO 80303.
Ridley,
B.A.,S.Madronich,
R.B.Chatfield,
J.G.Walega,
R.E.Shetter, D.R.Blake,
Department
ofChemistry,
University
ofCalifomia,
Irvine,
M.A.Carroll,
andD.D.Montzka,
Measurements
andmodel
simulations
CA92717.
ofthephotostationary
state
during
theMauna
LoaObservatory
Photo- J.D.Bradshaw
andS.T.Sandholm,
School
ofAtmospheric
Sciences,
chemistry
Experiment:
Implications
for radical
concentrations
and Georgia
Institute
ofTechnology,
Atlanta,
GA30332.
ozoneproduction
andlossrates,J. Geophys.
Res.,97, 10,375-10,388, B.C. Daube,D. J. Jacob,J. W. Munger,and S.C. Wofsy,Divisionof
1992.
AppliedSciences,
HarvardUniversity,Cambridge,
MA 02138.
Ritter,J.A., D.H. Stedman,andT.J. Kelly, Groundlevel measurements
of
G. L. Gregory,NASA LangleyResearch
Center,Hampton,VA 23665.
nitricoxide,nitrogendioxideandozonein ruralair, in Nitrogenous
Air
H. B. Singh,NASA AmesResearchCenter,Moffett Field,CA 94035.
R. W. Talbot,ComplexSystemsResearchCenter,Universityof New
Pollutants:ChemicalandBiologicalImplications,
editedby D. GrosjeHampshire,
Durham,NH 03824.
an, Butterworth,Stoneham,Mass., 1979.
Sandholm,
S.T., et al., Summertime
tropospheric
observations
relatedto
NxOy
distributions
andpartitioning,
J.Geophys.
Res.,
97,16,481-16,510,
1992.
(Received
August12, 1992; revisedAugust10, 1993;
Sandholm,
S.T.,etal.,Summertime
partitioning
andbudget
ofNOycom- accepted
August
10,1993)