University of New Hampshire
University of New Hampshire Scholars' Repository
Earth Sciences Scholarship
Earth Sciences
3-20-1999
Influence of biomass combustion emissions on the
distribution of acidic trace gases over the southern
Pacific basin during austral springtime
R. Talbot
University of New Hampshire, [email protected]
Jack E. Dibb
University of New Hampshire, [email protected]
Eric Scheuer
University of New Hampshire - Main Campus, [email protected]
D R. Blake
University of California, Irvine
N J. Blake
University of California, Irvine
See next page for additional authors
Follow this and additional works at: http://scholars.unh.edu/earthsci_facpub
Part of the Atmospheric Sciences Commons
Recommended Citation
Talbot, R. W., J. E. Dibb, E. M. Scheuer, D. R. Blake, N. J. Blake, G. L. Gregory, G. W. Sachse, J. D. Bradshaw, S. T. Sandholm, and H. B.
Singh (1999), Influence of biomass combustion emissions on the distribution of acidic trace gases over the southern Pacific basin
during austral springtime, J. Geophys. Res., 104(D5), 5623–5634, doi:10.1029/98JD00879.
This Article is brought to you for free and open access by the Earth Sciences at University of New Hampshire Scholars' Repository. It has been accepted
for inclusion in Earth Sciences Scholarship by an authorized administrator of University of New Hampshire Scholars' Repository. For more
information, please contact [email protected].
Authors
R. Talbot, Jack E. Dibb, Eric Scheuer, D R. Blake, N J. Blake, G L. Gregory, G W. Sachse, J D. Bradshaw, S T.
Sandholm, and H B. Singh
This article is available at University of New Hampshire Scholars' Repository: http://scholars.unh.edu/earthsci_facpub/128
JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 104, NO. D5, PAGES 5623-5634,MARCH 20, 1999
Influence
of biomass
combustion
emissions
on the distribution
of acidic trace gasesover the southern Pacific
basin during austral springtime
R. W. Talbot,• J. E. Dibb,• E. M. Scheuer,
• D. R. Blake,2N.J. Blake,2G. L. Gregory,
3
G. W. Sachse,
3J. D. Bradshaw,
4,sS. T. Sandholm,
4andH. B. Singh6
Abstract. This paperdescribes
the large-scaledistributions
of HNO3,HCOOH, andCH3COOH
overthe centraland SouthPacificbasinsduringthe PacificExploratoryMission-Tropics(PEMTropics)in australspringtime.Becauseof the remoteness
of thisregionfrom continentalareas,low
partper trillion by volume(pptv)mixingratiosof acidicgaseswereanticipatedto be pervasive
overthe SouthPacific basin.However,at altitudesof 2-12 km over the SouthPacific,air parcels
wereencountered
frequentlywith significantlyenhancedmixingratios(up to 1200pptv) of acidic
gases.Most of theseair parcelswerecenteredin the 3-7 km altituderangeandoccurredwithinthe
15ø-65øSlatitudinalband.The acidicgasesexhibitedan overallgeneralcorrelation
with CH3C1,
PAN, and03, suggestive
of photochemical
andbiomassburningsources.Therewasno correlation
or trendof acidicgaseswith commonindustrialtracercompounds
(e.g.,C2C14
or CH3CC13).
The
combustion
emissions
sampledoverthe SouthPacificbasinwererelativelyagedexhibiting
C2H2/COratiosin the rangeof 0.2-2.2 pptv/ppbv.The relationships
betweenacidicgasesandthis
ratioweresimilarto whatwasobservedin agedair parcels(i.e., >3-5 dayssincetheywereovera
continental
area)overthewesternNorthPacificduringthePacificExploratoryMission-West
Phases
A andB (PEM-WestA andB). In the SouthPacificmarineboundarylayera median
C2H2/COratioof 0.6 suggested
thatthisregionwasgenerallynot influencedby directinputsof
biomass
combustion
emissions.
Herewe observed
the lowestmixingratiosof acidicgases,with
medianvaluesof 14 pptvfor HNO3, 19 pptvfor HCOOH, and 18 pptvfor CH3COOH.These
valueswerecoincidentwith low mixingratiosof NOx(<10 pptv),CO (•50 pansper billion by
volume(ppbv)),03 (< 20 ppbv),andlong-livedhydrocarbons
(e.g.,C2H6<300 pptv).Overall,the
PEM-Tropicsdatasuggest
an importantinfluenceof agedbiomasscombustion
emissions
on the
distributions
of acidicgasesoverthe SouthPacificbasinin australspringtime.
1. Introduction
Acidicgasesareimportantparticipants
in tropospheric
chemical
processes.
They are major end productsof oxidativecycles,with
wet and dry removalof HNO3 and H2SO4 from the atmosphere
principalsinksfor tropospheric
NOx(NO + NO2) andSO2[Logan,
1983; Hales and Dana, 1979]. In remote regions the
monocarboxylicacids HCOOH and CH3COOH are often the
dominantacidicgasesandaciditycomponents
of cloudwaterand
precipitation[Keene et al., 1983; Andreae et al., 1988, 1990].
Formic acid is also a major sink for OH radicalsin cloudwater
[Jacob,1986].
Formicacidmay be producedby aqueousphaseOH oxidation
of hydratedformaldehyde(H2C(OH)2)in cloudwaterand subse-
mInstitute
fortheStudyof Earth,Oceans,
andSpace,Universityof New
Hampshire,Durham.
2Department
of Chemistry,Universityof California,Irvine.
'•NASALangleyResearch
Center,Hampton,
Virginia.
4Department
of EarthandAtmospheric
Science,
GeorgiaInstituteof
Technology,Atlanta.
5Deceased
June16, 1997.
6NASAAmesResearchCenter,Moffett Field,California.
Copyright1999by theAmericanGeophysical
Union.
quentlyprovidesan importantsourceof gasphaseHCOOH in the
remotetroposphere[Chameidesand Davis, 1983;Jacob, 1986].
Aqueousphaseproductionmechanisms
for CH3COOHappearto be
quiteslowandprobablyarea negligiblesourceof thisspecies
to the
troposphere[Jacob and WoJ•y, 1988]. The major sourcesof
HCOOH and CH3COOH to the globaltroposphere
appearto be
emissions
from combustion[Kawamura et al., 1985; Talbot et al.,
1988;Helaset al., 1992;Leferet al., 1994],vegetation[Keeneand
Galloway, 1986; Talbot et al., 1988, 1990], and possiblysoils
[Sanhuezaand Andreae, 1991; Talbot et al., 1995]. Permutation
reactionsof peroxy radicalshave been proposedas potentially
important sourcesof carboxylic acids [Madronich and Calvert,
1990; Madronich et al., 1990], but recent measurementsat a
continental site indicate that this pathway may be relatively
unimportant[Talbot et al., 1995].
There are potentially numerousproductionmechanismsfor
HNO3 in the troposphereincluding, NO2 + OH, recycling of
reactivenitrogenreservoirspecies,and evaporationof NO3' in
aerosol and aqueousphases[Roberts, 1995]. Many of these
processes
arethoughtto very slowin the uppertropicaltroposphere
dueto low 03 mixing ratiosand cold temperatures
retainingmost
of the reactivenitrogenin the form of NO during the daytime
[Folkinset al., 1995].
Measurements conducted in winter 1992 at 10-12 km altitude
betweenTahiti and California showedan abruptdecreasein the
Paper number98JD00879.
mixingratiosof 03 andNOy(i.e., the sumof reactivenitrogen
0148-0227/99/98JD-00879509.00
species)at the southernedgeof the IntertropicalConvergence
Zone
5623
5624
TALBOT ET AL.' ACIDIC GASES OVER THE SOUTHERN PACIFIC BASIN
(ITCZ) [Folkinset al., 1995].Owingto theremoteness
of the South
Pacificbasinfrom continentalareas,the observedtrendin O3and
NOyisnotsurprising.
In fact,lowmixingratioswouldbeexpected
to bepervasiveoverthe SouthPacificbasinfor mosttropospheric
tracespecies,includingacidicgases.
In this paperwe presentthe large-scaledistributions
of HNO•,
HCOOH, andCH•COOH overthecentralandSouthPacificbasins
during the NASA Global Tropospheric Experiment/Pacific
Exploratory Mission-Tropics(GTE/PEM-Tropics) in September/October1996.Objectivesof PEM-Tropicsincludedobtaining
baselinedata for importanttroposphericgases,evaluatingthe
oxidizingcapacityof thetroposphere
andfactorsinfluencingit, and
improvingour understanding
of the naturalsulfurcycle over the
South Pacific basin.
The firstpartof thispaperfocuseson the distributions
of acidic
flow, a diffuserwasmountedover the end of the inlet pipeparallel
to the DC-8 fuselage.This device provideda "shroud"effect,
slowingtheflow of ambientair throughit slightlybelowthetrueair
speedof the DC-8 andadding50-100 hPa of pressurization
to the
samplingmanifold.This effectivelyeliminatedthe reverseventuri
effect(•40 hPa)on the samplingmanifold.An additionalfeatureof
the diffuse was a curved step aroundthe manifold pipe which
provided the streamlineeffects of a backwardfacing inlet. Its
functionwasto facilitateexclusionof aerosolparticlesgreaterthan
• 2 •m in diameterfrom the samplingmanifold.Aerosolssmaller
thanthis were removedfrom the sampledair streamusinga 1
pore-sized
Zefluorteflonfilter thatwasreadilychangeable
every510 min to minimize aerosolloading on the filter and gas/aerosol
phasepartitioningfrom ambientconditions.
In addition to the features described above, the inlet manifold
addition
gases
inthe2-12knit,
altituderangewhichwereapparently
heavily wasequippedwith the capabilityfor conductinga standard
impactedby aged biomasscombustionemissions.Supporting
evidencefor this sourceis providedby coincidentdistributionsof
selected
hydrocarbon
compounds.
The distributionof acidicgases
is examinedin the marineboundarylayerandoverlyingtransition
region in the secondpart of this paper. Here there was little
evidence
for a directinfluenceof biomass
combustion
inputsonthe
chemistry,in starkcontrastto the middleanduppertroposphere.
Overall,thePEM-Tropicsmeasurements
provideuniqueinformationof thechemistry
of thisextensiveremoteregionduringaustral
springtime.
2. Experimental Methods
2.1. Study Area
ThePEM-Tropicsairborneexpeditionwasconducted
usingthe
NASA
Ames DC-8
research aircraft. Transit and intensive site
sciencemissionscomposed18 flights, averaging8-10 hoursin
durationandcoveringthealtituderangeof 0.3 to 12.5km. The base
of operations
for thesemissionsprogressed
asfollows: (1) Tahiti
(threemissions),(2) EasterIsland(two missions),
(3) Tahiti (one
mission),(4) New Zealand(one mission),and (5) Fiji (three
missions).
The datausedin thispaperwereobtainedin the geographicgrid approximatelyboundedby 60øN-75øSlatitudeand
165øE-105øWlongitude.Data obtainedon transitflights(eight
missions)
werealsoutilizedin thispaper.A geographic
mapof the
studyregionis shownin severalcompanion
papers[e.g.,Gregory
et al., thisissue;Hoell et al., this issue].
The overall scientificrationaleand descriptionof individual
aircraftmissions
is described
in thePEM-Tropicsoverviewpaper
[Hoellet al., thisissue].Thefeatures
of thelarge-scale
meteorological regimeand associated
air masstrajectoryanalysesfor the
September-October
1996timeperiodarepresented
by Fuelberget
al. [thisissue].
2.2. Samplingand Analytical Methodology
Acidicgasesweresubsampled
from a high-volume(500-1500
standardlitersper minute(sLpm))flow of ambientair usingthe
mist chambertechnique[Talbot et al., 1988, 1990, 1997a].The
subsample
flow ratewasalways<10% of theprimarymanifoldtotal
flow. Samplecollectionintervalswere typically4 min in the
of HNO• into the manifold ambientair stream.This spikewas
added• 10 cm downstreaminsidethe manifoldpipethrougha 6.5
mm OD glasscoatedstainlesssteeltubemountedperpendicular
to
theair flow. Thistubewas •20 mm longandmaintainedat 40øCto
facilitatepassingof calibrationgasthroughit. Througha tee, this
injectionlengthof tubingwas connectedto about1.5 m of heated
tubingthatwasdirectlylinkedto thepermovenoutput.Thisdesign
effectivelytestedthe passingefficiency of the entire manifold
system,whichwasindistinguishable
from 100 + 15%. The calibration systemfor HNO• consisted
of a permeationovenheldat 50øC
anda dilutionflow of ultra zero air (1.5 sLpm)which sweptthe
ovenoutflowto eithera nylonfilterforoutputquantification
or the
samplingmanifoldfor standardadditionon ambientair. The heated
tubingthroughwhichthe HNO• streampassedwas kept equilibratedby a flow designthat allowedthe calibrationgasto constantlypassto nearthe point of injectioninto the manifoldflow
beforebeingdumpedto wastethrougha retfirnline.The mixing
ratio of HNO3 in the 1.5 sLpm flow was typically200 partsper
billion by volume (ppbv). This spike was then dilutedseveral
hundred
timesby thehighflow rateof ambientair in thesampling
manifold,producingstandardadditionsof 100-1200pptv.Previouslywe havestudiedthe passingefficiencyof carboxylicacids
throughour inletmanifold,andfoundit to be >95% [Talbotet al.,
1992]. Thus we focused our attention on HNO3 due to its
importance
to thereactivenitrogencycleandtropospheric
chemistry.
The permeationoven output of HNO3 was monitoredon the
ground and in the air in near-realtime. We fabricateda new
calibrationsystemfor PEM-Tropicswhich maintainedthe permeationtubeto 50.0 + 0.1øC and 1850+ 1 hPapressure
at all altitudes.
The permeationsourcewas constantto + 8.5% over the courseof
theexpedition,with no equilibrationtime requiredat any altitude,
evenwith rapidchangessuchasduringspiralmaneuvers.
This new
designutilized upstreampressurecontrol(i.e., beforethe permeation tube) so that therewere no fittings, valves,or flow/pressure
controllersin-linebetweenthe tubeandthe injectionpoint into our
samplingmanifold.The flow throughthe ovenvariedfrom 20-25
cm3min'• depending
ontheambientpressure
andwasdilutedinto
the 1.5 sLpm flow describedabove. Standardadditionswere
conducted
with andwithouta teflon filter in-line to verify thatthe
filter did not influencethe passingefficiency of the sampling
boundarylayer, 6 min at 2-9 km altitude, and 8 min above9 km
manifold.
altitude,
reflecting
decreased
pumpingratesin themiddleandupper
troposphere.
The inlet manifoldconsisted
of a 0.9 m lengthof 41
mmID glasscoatedstainless
steelpipe.Thepipeextended
fromthe
DC-8 fuselageto provide a 90ø orientationto the ambientair
streamline
flow.To facilitatepumpingof thehigh-volume
manifold
Computer
controlledsyringepumpswereusedto movesample
solutionsin andoutof the mistchambersamplers
andoursample
containers.This essentiallyprovideda closedsystemof liquid
handling which greatly simplified contaminationcontrol.The
concentrations
of acidicgasesin our sampleswerequantifiedusing
TALBOT
ET AL.: ACIDIC
GASES OVER THE SOUTHERN
PACIFIC BASIN
5625
Asanexample
of thedetailed
verticalstructure
overtheSouth
selected
datafroma slowspiral(80mmin4) conducted
east
computer
interface
fordataacquisition.
Thesystem
wascomposed Pacific
combustion
plumewas
primarilyof Dionexcomponents
withthedetectors
andflowsystem of Fiji is shownin Figure4. An apparent
thermostated
to 40øC. Eluantswereconstantly
purgedwith He gas. sampled
near5 km,withcorresponding
largeincreases
in HNO3,
andC2H2/CO
butnotC2C14.
Noticetheveryrapidvertical
Nitric acid was measuredusinga fast anioncolumnwhile the C2H2,
in themixingratiosandgenerally
goodcorrespondence
carboxylic
acidsweredetermined
usinganAS4 column.Concentra- changes
HNO3andC2H2.Whiletheplumeswith largemixing
tor columnsandelectronicsuppression
wasusedin bothchroma- between
a custombuiltdualion chromatography
systemequipped
with a
tography
systems.
Calibration
curvesgenerated
onthegroundand ratiosof manytracegasesclearlystandout,the PEM-Tropicsdata
column
in the air agreedwithin ñ2%. We thuswere able to determine in generalsupportthe ideathat muchof the tropospheric
from 2-10 km altitudewas fumigatedwith varying degreesof
atmospheric
mixingratiosof acidicgasesin near-real
time.
In additionto datafor acidicgases,we presentselectedinformationonseveralimportanttracegasesincludingozone(03), carbon
monoxide(CO), ethyne(C2H2), perchloroethylene
(C2C14)
, and
peroxyacetylnitrate
(PAN). AerosolNO3' wasmeasured
on bulk
filter samplescollectedwith a forwardfacing isokinecticprobe
housedin a shroudto ensureisoaxial flow [Dibb et al., 1996a].
Ninety millimeterdiameter2 •m pore-sizedZefluorteflonfilters
wereusedasthe collectionsubstrate.
Specificdetailsregardingthe
measurementof various other speciesused in this paper are
presented
in companion
papers[Blakeet al., thisissue;Dibb et al.,
this issue;Gregoryet al., this issue;Vay et al., this issue].The
measurements
of thesespecieswere averagedto providemean
valuesthatcorresponded
directlyto the acidicgassamplingtimes.
Thismerged
dataproductwasgenerated
atHarvardUniversity,
and
it is usedexclusivelyin thispaper.
combustionemissions.The smoothshapeof the verticaldistributionof C2C14
istypicalof whatwasobserved
overtheSouthPacific
(Figure1), andit suggests
minimalinfluenceon thechemistryfrom
industrial emissions.The distribution of CH3CC13and other
halocarbonsalso supportsthis ascertain(N. Blake, personal
communication,1998).
To providea detaileddescriptionof the distributionof acidic
gasesoverthecentraland SouthPacificbasins,this informationis
presented
in a regionalsummaryformat(Table 1) consistent
with
that usedin companionpapers[Gregoryet al., this issue;Dibb et
al., thisissue].Informationon the distributionof many othertrace
gasescanbe foundin thesepapers,soit is not duplicatedhere.The
regionalbreakdownwasdevelopedto providedatasummaries
that
correspond
to logical latitudinaland longitudinalareas(e.g., the
ITCZ, andthe eastern,central,andwesternPacificbasins).In some
regionsthesamplingwasquitesparse,sointerregional
comparisons
need to be conducted with caution. On the basis of the vertical
3. Results
In the data presentedin this paper,obviousstratospherically
impactedvalueshavebeenremovedbasedon coincidentmeasurements of 03, CO, dew point, and selectedhydrocarbonsand
halocarbons.
This amountedto removinga total of about25 data
pointsobtainedon threedifferentflights.
The large-scalelatitudinaldistributionof acidicgasesoverthe
central and South Pacific basinsis presentedin Figure 1. It is
evidentfrom thesedistributionsthat numerousair parcelswere
encountered
between15ø and 60øS latitudewhich containedlarge
mixingratiosof acidicgases.The northernborderof theimpacted
Pacifictroposphere
appearsto be controlledby the presenceand
locationof theSouthPacificConvergence
Zone (SPCZ) [Gregory
et al., this issue].Nitric acid mixing ratios,for example,typically
decreased
by a factorof 2-5 in crossing
the SPCZregionfrom south
to north.This trendwas alsoapparentin othertracegasessuchas
CO, C2H2,C2H6,03, and PAN [Gregoryet al., this issue].Thus
pollutedair parcelsappearedto be presentsouthof the SPCZ with
"clean" air north of it fed by an easterlyflow regimealongthe
southernedgeof the ITCZ.
Mixing ratios of acidic gasesover the South Pacific were
generallylessthan200 pptvbutapproached
or exceeded1000pptv
in someair parcels.Theseair parcels(i.e., plumes)were observed
mainlybetween2 and7 km altitude(Figures2a-2c).Becauseof the
strongtradewind inversionoverthisregion,the marineboundary
layer exhibitedvery small mixing ratios of acidic gases.The
inversionappearedto be a very effectivebarrierto downward
mixingof acidicgasesfrom aloft. Indeed,the mostprocessed
(i.e.,
aging and mixing influences)air parcelswere sampledin the
marineboundarylayer.This featureof the datais illustratedusing
the ratio C2H2/COwhich had a medianvalue of 0.6 below 1 km
altitudebut showedsignificantlylargervaluesin the restof the
tropospheric
column(Figure3). Valuesof this ratio lessthan 1.0
are typicalof photochemically
agedand well mixed(diluted)air
parcels[Smythet al., 1998; Talbotet al., 1997b].
measurement
densityof acidicgases,thedatawerebrokenintofour
altitude bins: (1) the marine boundarylayer (<1 km), (2) the
transitionor cloudlayer(1-2 km), (3) the middle(2-8 km), and(4)
upper(8-12 km) troposphere.
As shownin the large-scaleverticaldistributions
(Table 1 and
Figure2), the smallestmixing ratiosof acidicgaseswere foundin
themarineboundarylayer.Heremedianmixingratioswere14 pptv
for HNO3, 19 pptv for HCOOH, and 18 pptv for CH3COOH.The
verysmallmixingratiosof HNO3 areconsistent
with the observed
NOxvaluesof only a few or sub(i.e, <1) pptvin theboundarylayer
(GeorgiaInstituteof TechnologyNO.•dataare availablefrom the
DistributedActive Archive Center (DAAC) at NASA Langley
ResearchCenter,Hampton,Virginia). There was no significant
regional differencein the mixing ratio of HNO3 in the marine
boundarylayer,but the carboxylicacidsexhibitedvalues2-3 times
larger in the centralPacificregion.In the middletroposphere
the
mixing ratios of acidic gasesshowedthe largestvalues in the
westernandcentralregions.This is consistent
with the generally
westerlyflow of air at thesealtitudesover the SouthPacificbasin,
implying that the leastprocessedair parcelswould be found in
theseregions[Fuelberget al., this issue].Most of the plumesthat
we sampledwere,in fact,encountered
overthe westernandcentral
Pacific areas.The easternPacific regionswere dominatedby
relatively"clean"air parcels.This longitudinaldifferenceseemingly reflectschemicaland physicallossesof acidicgasesas air
parcelstransverse
the Pacificbasinin a westerlyflow regime.
The mixing ratios of the carboxylic acids HCOOH and
CH3COOH are generallyfoundto be highly correlatedin the gas
andliquidphasesin the troposphere
[Keeneand Galloway,1986].
Over continentalareasthe ratio HCOOH/CH3COOH usuallyhasa
value near 2.0 with a correlation coefficient between these two
speciesnear0.9 [Keeneand Galloway, 1986; Talbot et al., 1988].
Although we observedlinear correlationsbetweenHCOOH and
CH3COOHoverthe Pacificbasin(Figures5a and 5b), they were
lessrobustthanwhat we observedduringthe PacificExploratory
Mission-WestPhasesA andB (PEM-West A andB) [Talbot et al.,
5626
TALBOT ET AL.' ACIDIC GASES OVER THE SOUTHERN PACIFIC BASIN
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Latitude
Figure1. Latitudinal
distribution
of acidicgases
at altitudes
of 2-12kmoverthecentralandsouthern
Pacific
basins.
1997a].
In some
oftheplumes,
HCOOHwashighlyenhanced
with
regard
toCH3COOH,
andtheratioHCOOH/CH3COOH
hadvalues
as largeas5.0 (plumemedianequalto 1.6).Thissuggests
the
possibility
of substantial
photochemical
production
of HCOOH
compared
to CH3COOH
(ormoreefficientlossof CH3COOH)
in
someof theplumesthatwe sampled
overtheSouthPacific.This
pointisfurtherexplored
in latersections
of thispaper.
4. Discussion
4.1. Altitude Range of 2-12 km
Thelarge-scale
impactof pollutionovermuchof thewesternand
dataset.Backward
trajectories
indicate
thatmanyof theairparcels
we sampled
hadnot beenovercontinental
areasfor 10-20days
[Fuelberget al., this issue].This is consistent
with the chemical
measurements
whichsuggest
thattheair parcelswerephotochemicallyagedandphysicallyprocessed
for a weekor two sincethe last
injection
of combustion
emissions.
Manyof thetrajectories
follow
a paththatimplies
thatthelastcontinental
areasthattheair parcels
passed
overwereBrazilandAfrica.Sincebiomass
burningoccurs
onbothof thesecontinental
areasduringaustralspring[Cahoonet
al., 1992], this is likely to be a majorsourceof combustion
emissions
overthePacificbasinat thistimeof year.
Methylchlorideis a reasonably
goodchemical
tracerof biomass
centralPacificbasins
is a significant
featureof thePEM-Tropics burningemissions
[Blakeet al., 1996].Therelationship
between
TALBOT
ET AL.' ACIDIC
GASES OVER THE SOUTHERN
12
PACIFIC
BASIN
5627
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I,
,
250
I
500
I
750
,
1000
CHsCOOH,pptv
Figure 2. Verticaldistribution
of acidicgasesoverthecentralandsouthernPacificbasins.Thesedistributions
showthat plumeencounters
with enhancedmixing ratiosof acidicgasescommonlyoccurredin the 3-7 km
altituderegion.
themixingratiosof CH3CIandacidicgasesisdepictedin Figure6. plumesmay be due to photochemicalproductionsincethe last
Theseplotsindicate
a generalrelationship
between
acidicgases
and scavengingevent.Evidencefor a photochemicalsourceof acidic
CH3CI(r2= 0.4).Theenhancements
of CH3CIin theplumes
are gasesis provided in Figures 7 and 8, where the relationships
smalldueto thesignificant
dilutionthesewell agedairparcelshave
undergone.
Plotsof C2H2andC2H6versus
CH3C1(notshown)show
similarrelationships
to thosein Figure6, againreflectingthe
substantial
processing
of theair parcelsovertheIndianandPacific
basins.
One featureof the plumesis the absenceof enhancements
in
aerosol
or aerosolassociated
species
[Dibbet al., thisissue],even
for ammonium
whichis releasedin largequantities
frombiomass
combustion
[Lobertet al., 1991]. Thisindicates
thattheair parcels
overthePacificbasinhavebeeneffectivelyscavenged
by clouds
and precipitation.
It also suggests,
sincemostacidicgasesare
highlywater-soluble,
thattheirlargemixingratiosin someof the
betweenthesespeciesand 03 and PAN are presented.As with
CH3CI,thetrendsareonlygeneral(r2near0.4) butsuggestive
of
photochemicalproduction of acidic gases.The break in the
relationshipsat <5 pptv of PAN is presumablydue to thermal
decomposition
of PAN to NOx at lower altitudes[Roberts,1995 ].
The datacorresponding
to <5 pptvPAN wasobtainedin the2-4 km
altitudebandwhereair temperatures
were typically280-285øK.
Plottingan individualspeciesasa functionof the ratio C2H2/CO
gives insighton the effect of air parcelprocessingon its mixing
ratio.Theserelationships
for acidicgasesare shownin Figure9. It
is evidentthat the relationshipis much tighter for the carboxylic
acidscomparedto HNO3, but it is unclearasto why this is the case.
5628
TALBOT ET AL.' ACIDIC GASES OVER THE SOUTHERN PACIFIC BASIN
12
ß
ß
eeee
e•ee
ß•
ß ee
ß
e•edl•
ß
ee
ß
ß
-,,,.... ,•..,..•.,,.
10
ß . .- ß
'
E
•
ee •
e•---ß •
ß
ß
ß e•eeeß ß
ß
ß •e •ee e'•
ß
'q•,.&•,f-...•
.,,'.
e'•ee ee • ß
ß
ß
ß
ß
ß
ß
'.l"l. ß"J'"•ß
I
ß .'
eee4e
ß 1,e e ,• eeeee
'
.:..a...•
. .. 4,'.•,=
ß..
l.
.*.
ß
4
ß
.
.
ß
.:-•:.....'-n.'' A
ß
ß: .
_
ß
ß ß ß ß eele
'...
ßß
-.-,,..x-,
.4.' ee ß "ße '
ß eß e• •
•
..
' '':
..- ,".
eeee
ß
e ß ß
ß
•,e..'
I..e ß ee eel.•.3,..
ß.&.• %'
a.
ß
e• ß el'
ß e•e,•e
ee
ee%
ß ß
8
ß
e• ee
e• ßß
.• ß ..e e
ß
ß
ß ee
ß e•
• ßß
ßße,e•e•e
e•e
•,.
ß 4•.- ß
e e ß
ß
ß
ß
,.
0.5
1.0
,
1.5
I
2.5
2.0
3.0
overa minimumof a oneweektimeframe.Thisis basedlargelyon
theabsence
of reactivehydrocarbons
(i.e., C4andhigher)in these
air parcels.It appearsthat mixingprocesses
(i.e., dilution)are
responsible
for muchof thevariationin individualspecies
mixing
ratiosandinter-relationships
between
variouscompounds.
Thus,air
parcelscanbe quitephotochemically
agedwith significantmixing
ratiosof secondary
speciesbut still appearmuchyounger(e.g.,
C2H2/CO> 1) dueto lessmixingwith background
air.
To examinethe potentialcombustionsourceof HNO3, only
mixingratiosgreaterthan100pptvareplottedversusCO andC2H2
(Figure10). Only in a few plumesdoesthereappearto be a direct
relationshipbetweenHNO3 and CO or C2H2. The largestmixing
ratiosof HNO3 occurredat relativelylow valuesof CO andC2H2
and correspond
to a C2H2/COratio near I (Figure9). In general,
therewasverysubstantial
amountsof HNO3in air parcelswith CO
of 50-100 ppbvand C2H2 <150 pptv. Togethertheseresultspoint
to significantphotochemicalproductionof HNO3 (sincethe last
scavenging
event)duringlong-rangetransportof air parcelsover
theSouthPacific.Similararguments
canbe madefor photochemical generationof carboxylicacidsin theseair parcels,especially
HCOOH. Previousmeasurements
of the ratioHCOOH/CH3COOH
in biomassburningplumestransported
longdistances
in the middle
troposphere
show
values
of
1.5-3
[Helas
et
al.,
1992;
Lefer et al.,
Figure 3. Vertical distributionof the ratio C2H2/COover the
1994; Dibb et al., 1996b].
central and southern Pacific basins.
Additionalmodelingstudiesare neededto enhanceour understanding
of photochemical
processes
occurringwithinplumesover
Clearly,thelargestmixingratiosof acidicgaseswerecontained
in theSouthPacificbasin.Limitedinsightasto whetherwe observed
the leastprocessed
air parcels(C2H2/CO>1). On the basisof the lossof CH3COOHin theseplumescanbe gleamedby examination
correlationsshownin this paper,it followsthat thesesameair of the CH3COOHand CH3OOH data.Plottingvarioussubsetsof
parcelsalsocontained
the largestmixingratiosof CH3CI,03, and thesedataobtainedoverthe SouthPacific(not shown)revealedno
PAN.It appears
thatthechemicalcomposition
of theseair parcels correspondence
betweenthe two species,aswouldbe expectedif
reflects
photochemical
activityof biomass
burningemissions
aged CH3COOHwerea significantdecomposition
sourceof CH3OOH
C2H2/ CO, pptv/ ppbv
12
I
'
I
'
I
'
I
'
I
'
12
I
'
I
'
I
,
I
'
I
,
I
'
I
,
I
'
I
,
I
'
E 10
-o
8
•:
6
=
4
a_
2
ß
I
o
70
,
I
80
,
90
I
,
100
I
•
I
110
,
120
I
130
140
o
0.9
,
1.0
1.1
E
I
'
I
,
I
'
I
,
I
'
I
,
1.3
I
1.4
1.5
C2H2/CO,pptv/ ppbv
C2H2, pptv
12
1.2
I
'
I
,
12
I
lO
'o
8 -
•:
6
'-,
4
a.
2
0
,
0
100
200
300
400
HNO3, pptv
I
500
,
0
600
0.5
,
I
1.0
,
I
I
1.5
2.0
,
2.5
C2CI4, pptv
Figure4. Verticaldistribution
of selected
tracegases
duringa slowspiralconducted
duringmission17justeast
of Fiji.
TALBOTET AL.' ACIDICGASESOVERTHESOUTHERN
PACIFICBASIN
5629
Table1. Regional
Summary
ofAcidic
Gases
OvertheCentral
and
Pacific Basins
Altitude,
HNO3
HCOOH,
km
CH3COOH
N
pptv
15 ø-45øN, 120o-170øW
< 1
1-2
2-8
8-12
13 q-8.5(10)
46 + 10(50)
87 + 43(83)
63 + 53(42)
45 +_18(50)
39 + 30(30)
72 + 49(55)
55 + 26(52)
55 q-23(60)
44 + 35(36)
72 + 45(59)
54 + 30(55)
< 1
1-2
2-8
8-12
20 ___
11(15)
52 q-14(49)
67 +_35(51)
150q- 107(107)
<1
1-2
2-8
8-12
18 q-10(17)
32 q- 14(30)
139q- 145(84)
63 q-63(37)
66 q-216(23)
44 q-20(43)
124q- 181(49)
61 q-54(46)
< 1
1-2
2-8
8-12
15 q-7.7(13)
40 q-3.0(40)
160q-124(97)
100q-61(81)
18 q-7.4(17)
50 q-5.0(50)
71 q-54(47)
66 q-32(52)
< 1
1-2
2-8
8-12
13 q-7.1(14)
28 q-8.2(30)
43 q-37(31)
45 q-30(45)
17
6
42
29
0o-15 øN, 120o-170oW
35 ___
30(27)
33 q-24(18)
31 +_14(33)
27 q-26(14)
34 q-23(20)
36 q-26(22)
33 +_14(35)
23 q- 19(13)
19
10
31
16
0o-35 øS,120o-170øW
84 q-293(27)
43 q-345(39)
84 q-81(54)
56 q-46(41)
40
21
192
122
17 q-8.1(15)
46 q-8.5(46)
84 q-70(53)
92 q-27(94)
12
2
46
19
16 q- 13(18)
67 q-47(47)
52 q-43(36)
42 q-26(43)
27
5
50
28
0o-35 øS, > 170 øW
0o-35 øS,80o-120øW
18 q-5.9(18)
33 q-8.5(32)
43 q-28(36)
54 q-41(39)
35 o-72øS, > 170 øW
< 1
1-2
2-8
8-12
14 q-4.6(14)
25 q-9.9(28)
180q-262(80)
54 +_71(25)
< 1
1-2
2-8
8-12
12 +_2.3 (11)
31 q-NA (31)
26 + 16(23)
38 q-60(9.0)
11 +__
4.1(10)
13 q-3.9(12)
38 q-26(33)
29 q-16(26)
162q-176(90) 114q-12(57)
54 q-39(40)
45 q-25(37)
23
13
70
23
35 o-72 øS,80 ø-I20 øW
16 q-4.4(18)
22 +_NA (22)
35 q-19(36)
18 q-5.0(19)
18 q-4.6(19)
20 q-NA (20)
33 q-18(26)
16 q-4.8(17)
7
1
16
5
Valuesare statedasmean-4-onestandard
deviation
(median).N represents
thenumberof datain altitude•in. NA meansnotapplicable.
1 ooo
(a) <2 km altitude
(b) 2 - 12 kmaltitude
ß
,,.f.;,
>
,
lOO
lOO
o
o
lO
ß•//•!:::
•COOH
=0.88
xCH3COOH
+3.1
'
ß
I I I I •
10
r2= 0.61
,
I
I
I
I I I I •
I
lO
I
100
CH3COOH,
pptv
CH3COOH,
pptv
Figure
5. Relationship
between
mixing
ratios
ofHCOOH
and
CH3COOH
over
thecentral
and
southern
Pacific
basins;(a) <2 kmand(b) 2-12kmaltitude.
5630
TALBOT ET AL.' ACIDIC GASES OVER THE SOUTHERN PACIFIC BASIN
burningplumes,thereis clearlymuchuncertaintysurrounding
the
productionand decompositionof carboxylic acids in such air
parcels.
I
1 ooo
ß
*
I.
ßß• =*
.:* . ßß ß
I ** ,%.. ø*
* .'. * *
- ... ßa,...ßf .....•,q,l;
• • .....
ß •,• , •'...<;.
".•,..*..
* ß*
ß.ß •,
•.••"•l,,j•&•_
'.,*
..
lOO
'.
.... :..'.
-..'.?.;i"g'--'
•71.•.-.. ,. :.
'.-*;:;,5:_'--':=_•:•:.'.:.'"
/
ß
lO
*
ß'
..
**
ß..
_ •*•..
.....
,•***e,. •,,t ..
ß ,•_,.•.... ** *. ....
ß ß ..-.q, I.ß.ß ß
. .:•....
ß
,....
:'?.
.ß
ßß
4.2 Altitude Range of 1-2 km
ß ß
The altitudeband<2 km was brokeninto the marineboundary
layer (<1 km) and the transitionor cloud layer from 1-2 km. The
mixing ratio of acidic gasesin thesetwo layersarc shownas a
functionof latitudein Figures 11a-11c. Nitric acid mixing ratios
wcrcsmallerat < 1 km comparedto 1-2 km altitude,exceptfor the
mostsoutherlydatawherethey wcrc aboutequal.There doesnot
*, ß
.
ß
ß
ß
ß
ß
HNO3= 10.0x CH3CI-26
'
ß
>
•
o
o
co
ß . .;.'..._..,•.•.....:
'
'
I
'
'
'
'
'
"
'
ß;,.•: <,.:.•..••,.'
.. •
ß" :•'_.....:•"••.37.•. ;%•: .':..' ';'": ß '
ß
,
ß
...
I
ß'. ß '.
..
.;•,..:
:•:'_••;C:.•,
,._:. <';• '.. ' • ;.,:'•'i•,•iK•t•'
ß.'
100
ß
O
•
'
ße ß
>
•..
100
10
'
1 ooo
1 ooo
%
ß 4'.
-
ß
10
:
•
ß
ee
ß ß ß
ß
ß
ee
ß
ß
ß
HNO3 = 1.2 x 0 3 - 0.25
HCOOH= 12.0x CH3CI-31
:
i
i
i
i
I
i
i
i
i
i
i
i
i
lO
I
lOO
1 ooo
1 ooo
>
>
•
100
lOO
o
o
o
o
co
10
i
HCOOH= 1.0x 03 + 0.02
CH3COOH= 9.0 x CH3Cl- 23
lO
i
lOO
6OO
CH3CI, pptv
1 ooo
Figure6. Relationships
between
mixingratiosof acidicgasesand
CH3C1in the altituderange2-12 km. The r2 valuesfor these
correlations
were•0.35. Particularly
for HCOOHandCH3COOH,
ß
.
lOO
thereis a general
trendof enhanced
mixingratiosat thelargest O
.
..,
&4.
...
' •,._', ::_'..
'.I,•>.';'%--•d'•
&.•v.•.•A._•;
"'• J
•'.•r;.._
ß•-
ß .-
,
: '""-' ..,'"l '.IhT.,,t•Ji.
llS•__"t•i•.'":
.":[/
valuesof CH3CI. Thesecorrelations
potentiallyindicatean
ß
important
biomass
burning
source
foracidicgases
overtheSouth co
..v.r-r,•
ß
Pacificbasin.Notethattheabscissas
arealsoa logarithmic
scale,
rangingfrom500 to 650 pptv.
...•..t'.',p..,•_:__t-;.,ß'_,
'. .
ß
t'•;..'
'
ß
CH•COOH
=0.84
x• +0.30
...
.
:
,
,
,
,
I
'10
•
,
,
•
,
•
,
,
I
'100
03, ppbv
[Madronich
andCalvert,1990].Thisresultappears
to support
a
significant
photochemical
source
ofHCOOHrather
thana predominanceof decomposition
of CH3COOH
in agedbiomass
burning Figure7. Relationships
between
mixingratiosof acidicgasesand
plumesovertheSouthPacific.We cannotruleout,however,some O3in thealtituderange2-12 km. Ther2valuesfor thesecorrela-
photochemical
productionof CH3COOHas well. Becauseof tionswere•0.40. Thesegeneralcorrelations
potentiallyindicatea
potentiallycomplex(andunknown)chemistry
in thesebiomass photochemical
sourcefor HCOOH andCH3COOH.
TALBOT
ET AL.' ACIDIC
GASES OVER THE SOUTHERN
PACIFIC BASIN
5631
altitude.In both layers,aerosolNO3' mixing ratioswere abouta
factor of 2 greaterthan those of HNO3 [Dibb et al., this issue],
presumablydue to uptakeof HNO3 onto sea-saltparticlesin the
marineboundarylayer[Huebert,1980] andpossiblyproductionof
aerosol-NO3'
from cloudprocessing
in the transitionlayer.
The mixing ratiosof carboxylicacidsin the marineboundary
layeroverthe SouthPacificwere aboutan orderof magnitudeless
thanthosepreviouslydeterminedfrom shipboardsamplingin the
centralNorthPacificregion[Arianderet al., 1990].This probably
1 ooo
lOO
lO
is due to the remoteness of the South Pacific basin from continental
,
,
,
, , , ,,1
,
,
i
, , i ill
10
'
'
i
areas and restricteddownward mixing acrossthe trade wind
i i i iii
100
1000
inversion.
Formic
and acetic acid did not exhibit a difference
in
their mixing ratiosbetweenthe marine boundaryand transition
layers.In the marineboundarylayer they had the largestmixing
ratiosnoah of the ITCZ. This may reflectthe closerproximityof
1000
_
ß
ß
ß ee
eeee
el e
els ß
ßß
ßß
ße ß ß eßeel•L ß ß
ß' .• .. ;2;.•;.}'."i':,. •
100
ß '
ß
ß . •..•.-.-•.;.,..•.•a,.j.,
•
1 ooo
i;.
..ß
._..:
•.•..
ß,..'....
'••.,.3,,'•..,'.
ß ''
10
'_.•.'7".
' ..
100
ß
HCOOH
= 0.39 x PAN + 1.1
lO
:
,
1
,
, , ,,,,I
,
,
,
, ,,,,i
10
i
100
,
i
i i 1111
1000
i
i
i
i
i
i
i
i
I
i
1
1 ooo
'
lOO
'
'
'
'
'
'
'
I
'
ß
1 ooo
.ß
o
o
e.e
ß
.'
(D
ß*At' _•/I'1'•ßß ß
ß
lO
.'..•g,qi.' ß
ß.' ,,..'.:•.•
lOO
(D
"
o
o
ß '.•
....
lO
;•
.
• ....
.' ,• •'.5 ,-....
e
e
PAN, pptv
1
I
I
I
I
I
I
I
I
o.1
I
I
1
Figure8. Relationships
betweenmixingratiosof acidicgasesand
PAN in the altituderange2-12 km. The r2 valuesfor these
correlations
were •0.40. Thesegeneralcorrelations
potentially
indicatea photochemical
sourcefor HCOOH and CH3COOH.
Mixing ratiosof PAN below• 5 pptvwereobservedin the altitude
range2-4 km,wherethermaldecomposition
of PAN wasapparently
1 ooo
significant.
.lie
ß ß ß . v . I,..:•;'•=:
lOO
o
o
appeartobeanysystematic
variationof HNO3mixingratiosat <1
km altitudewithlatitude.Althoughthedataaresomewhat
scattered,
HNO3mixingratiosappear
to increase
in thetransition
layergoing
fromsouth
tonorthlatitude.
Thisapparent
trendisdrivento a large
extent by the low values near 60øS. At midlatitudesand in the
ß ' .. l ;. "%". '
....
•'.':
ß.
o
ß
.'. '•'
,.e
v' ...
' .•;2•:7,:.' '"
•'½•,.•
ß
r•.'•
ß ß ß ßß ß
ß
ß.'......'.•.•-•
lO
' .
ßß •,' .
,:.
e•
.i.e
.
•
'
ß
ß
ß
(D
1
i
i
i
i
i
i
i
i
I
1
i
tropics
therewas2-3 timesmoreHNO3in thetransition
layerthan
C2H2 / GO, pptv/ ppbv
at<1 kmaltitude.
Thisobservation
couldberelatedto evaporation
of clouddroplets
releasing
HNO3to thegasphasein thetransition
layer.Thisprocess
wouldbe mostactiveneartheITCZ, whichis Figure 9. Distributionof the mixing ratiosof acidicgasesas a
wherethe largestmixing ratiosof HNO3 were observedat this functionof the ratio C2H2/CO.
5632
TALBOT
ET AL.' ACIDIC
GASES OVER THE SOUTHERN
1400
1400
1200
1200
PACIFIC
,
,
BASIN
,
,
,
1000
1000
>
8OO
05
0
o_
ee
6OO
800
ß
ßß
6OO
ß
ee
ß
ß
4OO
ß
ee
eel,
ß
ß
ß •
400
ß
ß
ß
ee• eee e• ß
ß
ß
200
'*
ß½•o.•..,....
ß
•ee
• e•e•.•.
•
eß e e
2OO
I
ß
ß
ß
ee
..•.
•.'
,
I
50
,
I
,
I
150
IO0
2( )0
I
0
,
100
I
,
I
2oo
co, ppbv
I
,
i
4OO
3oo
5OO
C2H2,pptv
Figure 10. Mixing ratio of HNO3 asa functionof CO andC2H2for HNO3 >100 pptv.
lOO
'
I
'
I
'
I
'
I
TransitionLayer (1-2 km)
'
I
I
15O
'
(a.)
.
'
I
'
I
'
i
I
(b.)
Transition Layer (1-2 km)
120
'
>
ß
•e
ß
ß
ß ee'ß
ß
0
60
c)
-i-
ß
.?
ß
o
-8o
lOO
,
I
,
-60
'
I
I
,
I
-40
'
I
,
-20
'
I
,
0
I
'
I
'
I
I
20
40
i
60
o
-8o
15o
I
,
I
,
-60
'
I
I
,
-40
'
I
I
,
-20
'
I
I
,
I
0
'
I
,
20
'
I
I
40
'
I
ß
Marine BoundaryLayer (<1 krn)
Marine Boundary Layer (<1 km)
12o
ß
ß
•e
ß
ß
ß
e, : ß eee•
e ß e ee ß e•e
ßI
o
-8o
I
,
-60
I
-40
,
I
,
-20
Latitude
I
0
,
I
20
,
I
40
0
-80
'
,
-60
I
-40
,
I
,
-20
I
0
,
I
,
20
Latitude
Figure 11. Latitudinaldistributionof acidicgasesin the marineboundarylayer(<1 kin) andthe overlying
transitionlayer(1-2 km). The solidlinesrepresenta plot of the medianmixingratiovalueas a functionof
latitude.
I
40
TALBOT ET AL.' ACIDIC
150
'
I
'
I
'
el
GASES OVER THE SOUTHERN
I
5633
Acknowledgments:
Wehonortheoutstanding
unselfish
contributions
of
ourcolleague
andfriendJohnBradshaw
(deceased)
totheoverallsuccess
and
accomplishments
of theGTE/PEM-Tropics
airborne
expedition.
Excellent
support
wasprovided
bytheground
andflightcrewsoftheNASAAmesDC8 aircraftThisresearch
wassupported
by theNASA GlobalTropospheric
'
(c.)
Transition Layer (1-2 km)
120
PACIFIC BASIN
Chemistryprogram.
'
ß
4
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• ß
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,
,
I
ß
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I
,
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I
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