Jan 20, 1994 - lines. These CO and CH 4 absorption signals are then sepa- rated by ..... and Figure 8 for additional discussion of the Pacific air influence).
JOURNAL OF GEOPHYSICAL
RESEARCH, VOL. 99, NO. D1, PAGES 1659-1669, JANUARY
20, 1994
Carbon monoxide and methane over Canada: July-August 1990 R. C. Harriss, G. W. Sachse2 j E. Collins Jr. 2 L. Wade,5 K B. Bartlett, R. W. Talbot, E. V. Browell, 2 L. A. Bartie,4 G. F. Hill,2 andL. G. Burney s Carbonmonoxide(CO) andmethane(CH4)weremeasured in the 0.15- to 6-kin portionof the troposphereover subarcticand boreal landscapesof midcontinentand easternCanadaduring JulyAugust 1990. In the mid-continent region, Arctic air entering the region was characterized by relativelyuniformCO concentrations (86-108 partsper billion by volume(ppbv)) andCHnconcentrations(1729-1764 ppbv). Local biomassburningandlong-rangetransportof CO into the areafrom industrial/urbansourcesand distant fires did frequently produce enhancedand variable concentra-
tions. Emissionsof CHnfrom the HudsonBay lowlandswasthe primarysourcefor enhancedand variable concentrations,especiallyat altitudesof 0.15-1 km. In easternCanada,most of the observed
variabilityin CO andCHn wassimilarin originto the phenomena describedfor the midcontinent region. However,unexpectedly low concentrations of CO (51 ppbv) and CH4 (1688 ppbv) were
measured in themidtroposphere on several flights. Combined meteorological andchemical data indicatedthat the low CO-CHn eventswerethe resultof long-rangetransportof tropicalPacific marine
air to subarctic
latitudes.
1. INTRODUCTION
tionsof CO andCHnmeasured overtheseremoteregionsof
This paper reports the results of a study of surfacesources and atmospheric transport processes which influenced the spatial and temporal variability of troposphericcarbonmon-
oxide(CO) andmethane(CHn)overregionsof centraland eastern Canada during July-August 1990. The regions studied are some of the most remote areasremaining on the North American
continent.
We documented
variable
concentra-
tions of both CO (50-466 partsper billion by volume (ppbv))
andCHn(1688-1841ppbv)at altitudesof 0.15-6 kin, over relatively pristine subarcticand boreal landscapes. Meteorological factors and local surface emission sources explained most of the observed chemical variability. During summer months the polar front frequently retreats from theseregions and is replaced by a complex interaction of air massesfrom northwesterly, westerly, and southwesterly to southerly directions. Inflow from the northwest transits several thousand kilometers of landscape (Alaska to north central Canada) with a high incidence of uncontrolled wildfires. Southerlyflow to the CanadianHudsonBay region has passedover regions of American industrial and urban emissions. We will show that the long-range transportof pollutants from these upwind continental sources,combined with
emissions of CHnandCO fromlocalwetlandsandfromlocal wildfires, produced the enhanced and variable concentra-
North
America.
The rationale and principal objectives for the NASA Arctic Boundary Layer Expeditions (ABLE 3A and 3B) are discussedby Harriss et al. [ 1992b, this issue]. The airborne
CO andCHnmeasurements madeduringABLE3 arerelevant to obtaining a better understanding of regional sources, sinks, and distributions of these gases in remote areas of North America which have not previously been studied in any detail. Previousintensive studiesin subarcticand Arctic areas during summer months have been located at coastal sites like Point Barrow, Alaska, or Cape Meats, Oregon to minimize the effects of specific continental sources [e.g., Khalil
and Rasmussen, 1984; Steele et al., 1987].
Most
studieshave been over the more industrialized regions of the United States and Canada to assess"near-source"pollution chemistry [e.g., Boatman et al., 1989; Blumenthal et al., 1984; Dickerson et al., 1987]. 2. Tim ARCTICBOUNDARYLAYEREXPEDITION(ABLE) 3B The NASA
ABLE
3B conducted
an intensive
air chemis-
try measurement program in the midcontinent and eastern regions of Canada during July 6-August 15, 1990. The midcontinent component of ABLE 3B was closely coordinated with the CanadianNorthern Wetlands Study (NOWES) ground-basedand aircraft sampling activities in the vicinity of Kinosheo Lake in the Hudson Bay lowlands and at
•Institute fortheStudyof Earth,Oceans, andSpace, University Fraserdale, Ontario, during July 6-July 30. During this of New Hampshire,Durham.
period the NASA Electra aircraft was based in North Bay,
2NASALangleyResearch Center,Hampton, Virginia. Ontario, approximately 700 km south of the primary study 3Lockheed Engineering andScience, Hampton, Virginia. areas (Figure 1). The midcontinent portion of the ABLE 3B 4Atmospherie EnvironmentService, Downsview,Ontario, campaign included five aircraft missions to the Kinosheo Canada.
Lake and Fraserdale area, with considerable time devoted to
sSTCCorporation, Hampton, Virginia.
measurements of CO, CHn, andO3 atmosphere-biosphere exchange [Ritter et al., this issue]. Three missions were devotedto a regional survey of air chemistry from approximately 46øN (North Bay) to 59øN (Churchill, Manitoba). During the July 30 to August 15 period of the ABLE 3B the NASA Electra aircraft was basedin GooseBay, Labra-
Copyright1994by the AmericanGeophysical Union. Paper number93JD01906. 0148-0227/94/93
JD-01906505.00 1659
BARRISS ETAL.: CO ANDCH,,OVERCANADA
1660
dor. Five missions were conducted in the vicinity of reduced pressureof 125 tort to minimize potential overlap Schefferville, Quebec, where the ABLE 3B had established from undesired gas absorption lines. The outputs of two
a ground-basedair chemistrymeasurementsite (Figure 1). TDLs(onelasingin the7.6-ginCH4bandandtheotherin the Two air chemistrysurveymissionswereflownin thevicin- 4.7 gm CO band) are beam combined by a dichroic beam ity of GooseBay, overthe wetlandsof southeastern Labra- splitter and then directedthroughthe White cell. Througha dor and over the Atlantic Ocean. The final five flights of combinationof temperatureand laser current tuning, the ABLE 3B were dedicated to a latitudinal survey along the east coast of North America from 63ø44'N (Frobisher Bay) to 37ø3'N (Hampton, Virginia).
wavelengthsof the two TDLs are fine tuned to their respec-
A morecompletedescriptionof theABLE 3B-NOWESis presented by Harrisset a/.[thisissue]andRouletet al. [this issue]. A companiondataseton CO andCH4 in the troposphereover Alaskaandareasof theNorth AmericanArctic
of the TDLs acrosstheseisolatedCO and CH4 absorption features.If CO andCH4 molecules arepresentalongthe
was obtainedin ABLE 3A (July-August 1988) and reported by Harriss et al. [1992a]. 3.
EXPERIMENTAL METHODS
tiveCO andCH4absorption lines. Rapidmodulation of the lasercurrents(-10 kHz) repetitively sweepsthe wavelengths
absorption path, the two laser beams will be periodically attenuated as the TDL wavelengths cross the absorption
lines. TheseCO andCH4absorption signalsarethenseparated by anotherdichroic beam splitter and thesebeamsare detectedby two InSb detectors. For typical ambient levels the absorptionsignalmagnitudesare proportionalto the CO
andCH4mixingratios. Calibrationof instrument response AirborneCO andCH4 datawereprovidedby a tunable and zero offset is accomplished by periodically flowing diode laser (TDL) instrument denotedas DACOM (differencalibrationgasof knownCO andCH4 concentrations and tial absorptionCO measurement).The DACOM instrument, zero air through the White cell. During ABLE 3B DACOM operatedin two air sampling which was describedin detail by Sachseet al. [ 1987, 1991], has provided CO measurementsin several Global Tropo- modes, a slow responsemode optimized for high-precision sphericExperimentexpeditionsincludingChemicalInstru- concentration measurementsand a fast responsemode optimentation Test and Evaluation (CITE) 1, CITE 3, ABLE 2A, mized for eddy correlation flux measurements.Most of the ABLE 2B, and ABLE 3A. For the ABLE 3 expeditions, data discussedin this paper were taken in the slow response DACOM's capabilities were expanded to simultaneously mode,while the CO and CH4 flux resultsare reportedby Ritter et al. [this issue]. In the slow response mode an measureCO andCH4. Measurementsby DACOM use a continuousflow of air airflow of 5 standardliters per minute is thermally condifrom the free airstream drawn through an inlet and subse- tionedby a heat exchanger andH20(V) is removedby a
of 5-s quentlythrougha 1.5 L White cell containinga 20-m folded PermaPurepermeationtubedryer.A 1/etimeresponse optical path. The White cell pressureis maintained at a andmeasurement precisions of +0.1%CH4(lo) andñ1%CO
Frobisher
Mission
Ba'
6
Fig. 1. Map of the Arctic BoundaryLayer Expedition(ABLE) 3B study areas.
1661
HARRISS ETAL.' CO ANDCH4 OVERCANADA ABLE 3B verticalprofile of CO and CH4 near Moosoneeduringflight3
(10) were achievedfor 5-s averageddata. The datareported in this paper represent5-s or 90-s averageCO and CHn values. DACOM working standardswere calibratedagainst mastergascylindersgravimetricallyproducedat theNOAA/ CMDL, Boulder, Colorado. The accuracies of the working
standards are+1.0 % CO and+1% CHn. 4.
THE MIDCONTINENT
The location of the ABLE 3B flights 2-9 in the midconti-
nentregionof Canadawas,in part,to provideanopportunity to study variations in air chemistryassociatedwith the dynamicinteractionof the summerpolarfront andthecircumpolarwesterlies. During summermonthsthe Pacific westerlies that dominate the southern regions of interior Canadaare derivedprimarily from subsidenceof high-level westerliesthat descendeastof the Rocky Mountains. As the westerlies move across interior North America at altitudes
of 1-11 km, they becomean entrainingor confluentcurrent;
they interactwith Arctic airstreamson their left flank and tropicalor subtropicalairstreams on theright flank. These interactionsoften result in thermodynamicinstabilities and intensiveconvectiveactivity alongfrontal boundaries.Active vertical transportof atmospherictrace gas and aerosol
, ] , , I • ß i i I [ f I ' I .... 1600 1650 1700 1750
I .... 1800
I ..... 1850 1900
CH4 (ppbv) I • , ,
50
, I .....
100
I , ,
150
,
,
I
,
,
• , I • • • , I
200
250
300
....
350
CO (ppbv)
speciesis associated with convectiveactivity[e.g.,Knupp, 1987; Dickerson et al., 1987]. During summermonths the
Fig.3. Verticaldistributionof CO andCH4observed nearMoosonce,
ABLE 3B North Bay locationwasnicely locatedfor inves-
Ontario, July 11, 1990.
tigating, (1) the regional scale chemistryof Arctic airstreams penetrating south into the North American midcontinent,(2) the influence of air massinteractionsand
Analyzed48 HoursBack-Trajectories Moosonee,July 11, 1990 12Z Level
A 700 mb
O 850 mb
[] 925 mb
long-rangetransporton the distributionof trace gas and aerosolspecies,especiallyin the 0.15- to 6-km regionof the troposphere, and(3) thechemistryof freetropospheric westerly airstreams.
In the following sectionswe first use a combinationof aircraftandground-based datato characterizeCO andCHn concentrationsin a variety of air masses. Emissionfactors for a tundra fire are documentedin a following section. We concludewith a brief summarydiscussionof variations in
COandCHnin thesummer months across thehighlatitudes of North
America.
4.1. Arctic
Air
The ABLE 3B and the NOWES ground-basedair chemis-
try site at Fraserdalesampledboundarylayer air flowing into the midcontinentregion from the Arctic on July 11 (flight 3) and 21 (flight 5). In both cases,air trajectory analysisindicatedat least2 daysof northerlyflow into the lower troposphereover the samplingsitesprior to the measurements we hereclassifyasArctic air. Examplesof Arctic air trajectoriesareillustratedin Figure2. Theseair masses were also characterizedby low concentrationsof both gas
(CHn,CO,NOx,NOy)andaerosol species [e.g.,Browell et
al., this issue, Talbot et al., this issue]. The vertical distri-
butionsof CO andCHn,representative of Arcticair masses studied in ABLE 3B, are shown in Figure 3. Aerosol sulfate concentrationsprovide an independent
index of levels of anthropogenicpollution. A time seriesof ground-based aerosol sulfate measurements taken at Fraserdaleare shownin Figure 4. On both July 11 and21 and severaldaysprecedingeachdate, surfacesamplingrecorded
z
85 ø W
65 ø W 75 ø W
low sulfate
concentrations.
It is importantto note that while the Arctic air character-
Fig. 2. Analyzed 48-hourbacktrajectories for July11, 1990, ized in ABLE 3 has uniform and relatively low concentraMoosonce, Ontario
tions of CO throughoutthe 0.15- to 6-km portion of the
1662
HARRISS ETAL.: CO ANDCH,•OVERCANADA
14004
•1•. 1200
• 10001 8o0 • 600
4øø 1
Fig. 4. Daily aerosol sulfate concentrationsmeasuredat Fraserdale, Ontario
troposphere, the air has undoubtedly been influenced by pollution from human activities at some point in the past (daysto weekspreviously). Polluted air is transportedto the Arctic in both midtropospherichaze layers and larger-scale subsidenceof air from the upper tropospherewhich originated in regions of midlatitude cyclonic activity. In the polar region where sourcesof anthropogenicpollution are minimal, the previouslypolluted air becomeswell mixed by mesoscaleprocesses. Average Arctic air CO concentrations in the Canadian midcontinentregion were 96 (July 11) and 98 ppbv (July 21),
witharangeof 86-108ppbv.Averageconcentrations of CH4 for the same data set were 1753 ppbv (July 11) and 1746 ppbv (July 21), with a range of 1729-1764 ppbv. In the ABLE 3A in Alaska andregionsof the CanadianArctic, CO in Arctic tropospheric air was observed to have a similar concentrationrange of 88-100 ppbv [Harriss et al., 1992a]. Methane concentrationsin Alaska rangedfrom 1720 to 2096 ppbv in air with Arctic characteristics. The variability in
derivedprimarilyfroma flamingfire front,with secondary input fromalreadyburned,smoldering areas.Plotsof fastresponse CO
andCHndata(Figure 5a)andthe"excess" CHnversus "excess" CO (Figure5b) illustratethevariabilitymeasured in a plumesampled
fromupwindto downwind.The"excess" orACH•andACOare derivedby subtractingambientbackgroundconcentrations of 1795ppbvand137ppbv,respectively, fromhigherconcentrations measuredin the smokeplume.
TheACHe/ACO emission ratioderived fromthedatainFigure 5bisapproximately 0.10.A statistical analysis ofthecomplete fast response datasetfor enhanced plumeconcentrations (n = 397) yieldedanr• = 0.87. Previous measurements ofACH4/ACO mean emissionratios from controlledbums in the boreal region of Canadaalso resultedin an averageof 0.1 for flaming and smolderingfires [Cofer et al., 1991]. 4.3.
Industrial/Urban
E•nissions
One of the objectives of the ABLE 3 program was to
CH4concentrations is primarilyrelatedto therole of north- explore the impacts of human activities on the chemical em wetlandsas a sourceof atmospheric CH4 [Sebacheret compositionof the North American troposphere[Harriss et
al., 1992b]. It is interestingthereforeto comparethe composition of inflowing Arctic air to outflow air exiting the ambientCH4concentrations occurred in a stableatmospheric eastcoastof North America. On the final ABLE 3B flight boundary layer with an inversion at an altitude of 1 km or (flight 22, August 15) an air mass was sampledoff the
al., 1986; Whalen andReeburgh, 1988; Harriss et al., 1992a; Ritter et al., this issue;Roulet et al., this issue]. The highest
lower and an underlying flooded wetland surface environment.
4.2.
Tundra
Fire
Emissions
On July 26 (flight 9) the NASA aircraft sampled the smokeplumeof a tundrafire burningin thevicinityof theNOWES KinosheoLake air chemistrysite. The fire hadbeenburningfor severaldaysin a relativelylimited areaestimatedto be approximately 10 ha. At the time of sampling,the smokeplume was
Virginia coast which had moved across the eastern United
Statesfrom the HudsonBay region. This air massprovides qualitative insights into how urban/industrial emissions
modify the CO and CH• concentrations and ratiosin the troposphere.
Verticalprofilesof CO andCHnat a locationapproximately 10 km eastof the Virginia coastare shownin Figure 6. A comparisonwith Arctic air (Figure 3) showedsignificant enhancementsin the concentrationsof both gasesat
HARRISS ETAL.' COANDCH4OVER CANADA
1663
(a)
JULY 26, FLT 9- NEAR KINOSHEO LAKE FIRE PLUME 1920
1400
CH4 • COI 1-1200 1000
-800
-1-
1840-
-600
-400
1800 _._-,_•• 1780
22:00
22:01
....
22103 22:04 "
22106
22':07
' 22:09
22:10
TIME
(b)
JULY 26, FLT 9 NEAR KINOSHEO LAKE FIRE PLUME 140
>n120• 100'--
80-
!
3:
60-
3:40
0
03
20
o -2O
0
200
400
600
800
1000
1200
EXCESSCO (CO- 137;ppbv)
Fig.5. (a)Concentrations ofCOandCH4measured ina smoke plume at 150mabove a tundra firenearKinosheo Lake,Ontario. (b)PlotofCH4 (measured-local background) versusCO for thefire plumedatain Figure5a.
altitudes below3.5kin. From3.5to5 kmtheCOandCHn wascharacterizedby unexpectedlow concentrationsof trace concentrationsin the Virginia profile were lower than in Arctic
air.
gasesandhigherwatervaporthanpreviouslyreportedfrom the midlatitudesof the easternUnited States(seesection5
Supporting datafromtheUV differentialabsorption lidar and Figure 8 for additional discussion of the Pacific air (DIAL) [Browellet al., thisissue]andmeteorological mea- influence). Theenhanced concentrations of COandCH4
surements aboardthe aircraftprovideinsightsinto the fac-
below 3.5 km are expected for a site downwind of the
torsdetermining thedistributions ofCOandCHninFigure 6. northeastern UnitedStates.However,therelationships beTherelatively lowconcentrations ofCOandCH4above 3.5 tweenCOandCH4arecomplex, reflecting theinfluence ofatleast km wereassociated with Pacifictropicalair whichhadbeen threedifferentair masses.A UV DIAL imageof aerosoland transported acrosstheUnitedStatesin themiddleandupper ozonedistributionsin the vicinity of the Figure6 vertical tropospheric westerlies[Shiphamet al., thisissue]. This air profile providesinsights intothespatialcharacteristics of theair
HARRISS ETAL.: CO ANDCH• OVERCANADA
1664
LATITUDINAL
SURVEY
ABLE=3B
PORTLAND FLIGHT
TO LANGLEY
22
15 AUG
RC 1990
RELATIVE AEROSOL SCATTERING X 1000 (IR) 0
6
12
18
24
3O
I
I
I
I
I
I
13:20 I ,
,
,
13:30 I ,
,
i
13:40 I
,
i
LT
PT3 I
u•
4-
-4
•
3-
-3
CI
2-
-2
-1 /
-o
38.15
37.88
N LAT
38.26
' I
i
-75.41
-75.46
E LON
-74.57
OZONE (PPBV) 20
o
40
I
13:20 I •
60
I
,
,
80
I
,
13:30 I ,
lOO I
I
13:40 i
i
,
LT
I
PT3 I
-4
-3 m
-2
2-
-1 -0
38.15
I
I
-75.41
37.88
I
I
I
I
I
I
-75.46
38.26
,
'
,'
,'
,'
N LAT
I
I
-74.57
E LON
Plate 1. Remotely sensedaerosoland ozone distributionsdownwind of easternVirginia on August 15, 1990.
1665
HARRISS ETAL.' CO ANDCHsOv• CANADA
mixedlayeris beingdisturbed by convective activity,and theenhanced aerosol, CO,andCH4concentrations at2.5-3.0 km areprobablyproducts of convective pumping intothe
ABLE 3B verticalprofileof CO and CH4 off coastof Virginiaduringflight22
free troposphere. CO
Thetroposphere overeasternVirginiais influenced by a
CH4
widevarietyof CH4andCOsources, Combustion of fossil fuels would be the dominant source of CO, and a secondary
source of CH4. Theprimarysources of CH4in theregion
4
wouldbe landfills,sewagetreatmentplants,leakingnatural
(--,,,.
gasdistribution systems, andnaturalwetlands.Linearregression analysis of theCO andCH4 datafromFigure6 indicateda significantcorrelationwith an r2 = 0.93. The
CH4/CO ratioderived fromtheslope oftheregression line was0.84,indicating anenrichment of CH4relativeto COin industrial/urbanemissionscomparedto tundra fires.
5. EASTERN CANADA
1650
1600 I
50
....
•
,
100
1700 ,
,
, I
,
1750
1800
OH4 (ppbv] ,
,
150
• I
• ,
,
200
• I
1850
• • • '
250
I
1900
....
300
J
From July 30 to August14 the ABLE 3B aircraftwas basedin GooseBay, Labrador. The studyarea in eastern Canada'wassimilar in manyrespectsto the midcontinent
region.Tropospheric chemistry overtheLabrador-Quebec regionwasinfluenced by intrusions of Arcticair, westerly
350
CO (ppbv)
inflow which had traversedthe continent and was variable in
andsoutherly tosouthwesterly inflowpolluted Fig.6. Verticaldistribution of COandCH4overeastern Virginia composition, on August 15, 1990.
by industrial andurbanemissions frombothU.S. andCanadian sources. Forest and tundra fire emissions were also a
localsourceof tracegasesandaerosols in easternCanada.A
masses whichdetermine theCOandCH4concentrations. The comprehensive discussion of thechemistry of pollutedairin locationof theFigure6 verticalprofileis shownasPT 3 on the Goose Bay-Schefferville region can be foundin other thePlate! DIAL image.The atmospheric mixedlayer,with papers in this issue [Wofsy et al., this issue; Bakwinet al., highaerosol andozone,is 0-2 km. Thereis a secondary this issue; Talbot et al., this issue]. A summary of CO and aerosollayerat 2.5-3.0km. Bothof theselayersexhibit in polluted airovereastern Canada is enhanced concentrations ofbothCOandCH4. A particularly CH4concentrations in Figure7. significant enhancement of CH4occurs at2.5-2.75km. The presented
EASTERN CANADA- "POLLUTED" AIR MASSES
90 second averages URBAN POLLUTION
E3
o.
1
1
-IBIOMASS
I 1720
BURNING 100
120
140
160
180 200 CO (ppb)
220
240
260
Fig.7. Summary of90-second average COandCH4 concentrations inpolluted airsampled over Quebec andLabrador, August 1990.
1666
HARRISS ETAL.' CO ANDCH• OVERCANADA
TABLE 1. Summary Statistics for Air Masses Identified As Tropical Pacific Marine in Origin, Detectedat 2-6 km Altitudes Over Eastern Canada, August 1990 (Flights 14, 15, and 17).
....................
Species Mean
' c'O CH4
s.d.
Median
N
Uncontrolled
fires
in remote
subarctic
and Arctic
areas
produced episodic, irregular enhancements of CO during summermonths (Figures 9b and 9c). Fire control measures largely precludedsuchenhancementsin an urbanizedregion
Range likeNorthBay. (3) Unexpectedly lowconcentrations of 50-
..... 5'1'.6"_92.7 75ppbvCOweremeasured in thetroposphere overeastern ' (•9" 6.9...... 68'' '1493 1717
7.6
1718
All concentrationsare in ppbv.
1493 ....
1688-1738 Canada(Figure9c) but alwaysat altitudesgreaterthan2000 m abovethe surface. On severalflights theselow concentra-
tions were found to represent 30-50 % of the tropospheric column. To our knowledge, suchlow concentrationsof CO have not been previously reported from this region. The occurrence of unusually low concentrations of CO Methane concentrations generally decreasedwith altiand CHn between0.15 and 6 km was uniqueto eastern tude as expected (Figures 10a-10d). This tendencyreflects Canada and the east coast of North America during ABLE 3B. Table 1 summarizes some characteristics of tropo- the presenceof active surface sourcesin all of the regions spheric air massessampled over eastern Canada which ex- studiedby ABLE 3B. However, severalunexpectedfeatures
are: (1) Thevariability hibitedunexpectedlylow concentrations of CO and CH4. in theABLE3B CHndatasummaries did not decreasewith altitudeas Theseair masseswerealsocharacterized by low O3concen- of CH4 concentrations trations, and their spatial distribution over the entire tropospheric column could be determined with the UV DIAL
expected for this long-lived tracegas. In fact, the datafrom severallocationsin Canadaexhibitconsiderablevariabilityin the 2- to 6-km portionof thecolumn(Figure10a-10c). (2) The 1700
remotelysensedO3 data [see Browell et el., this issue]. observedat approximately 3 km Figure8 documents a low CO-CHneventfrom3.0 to 5.5 km. ppbvCHn concentrations The combined chemical and meteorological analyses for these events indicated long-range transport of tropical Pacific marine air to the ABLE 3B study area in eastern subarcticandmidlatitudeNorth America[seeShiphamet el., this issue;Blake et el., this issue;Browell et el., this issue].
6.
over easternCanada were unusually low for a high-latitude region of the northern hemisphere (Figure 10c). It will be important to determine how often incursions of tropical marine air occur at these high northern latitudes.
Acknowledgments. The first author of this paper owes special thanks to the two reviewers who had to struggle through a very poor quality first edition of this manuscript.
SUMMARY AND CONCLUSIONS
Their
The ABLE 3 studies in July-August 1988 and 1990 provided the first relatively large combined trace gas and aerosol data basesfor the northernhigh latitudes of North America for summer
conditions.
The case studies
described
comments
resulted
in
a total
rewrite
and a much
improved paper. Diana Wright patiently and carefully typed many versions of this paper.
in this
paper and by Herriss et el. [19924] document a more than ninefold variation in CO and an approximately 10 % varia-
ABLE 3B vertical profileof CO and CH4 over Scheffervilleduringflight 14
tion in CH4in regionsrelativelyremotefromhumanactivities. Enhancedconcentrations of CO and CH4 originated from threeprimary sources,CO and CH4 emissionsfrom local forest and tundra fires, CHn emissionsfrom local wetlands,andlong-rangetransportof CO andCHnto north-
CO
j CH4
ern high latitudes from midlatitude industrial and urban
sources.Unusuallylow concentrations of CO andCHnwere
I
associatedwith long-range transportof tropical marine air to northern high latitudes. Mesoscale interactions of meteorological and chemical processestypically determined local
#o•o
e•eoe• e
variabilityin bothCO andCHnthroughout thesubarcticand Arctic regions during summer months. In Figures 94-9d and 10a-10d we presentstatistical sum-
mariesof theABLE 3B CO andCH4concentration datafrom the two intensive 1990 study areas in Canada. These minimum, maximum, and average concentrations for various regions are summarizedto assistin future comparisonswith other field
measurements
and with model-derived
estimates
of CO andCHn. Theyalsosummarize theregionalvariability in these gasesover our 6-week sampling period. In comparing the summary CO distributions for the regions studied in ABLE 3B several observationscan be made: (1) The average CO concentrations at North Bay, Ontario (46øN), decrease with altitude. These profiles reflect the influence of local and regional industrial and urban emissions in and around the North Bay area (Figure 94). (2)
ß
.... o 1600
1650
I
....
1700
I
....
I
I
I
I
,
,
,
1750
i
I
i
,
I
1800
i
{
i
i
i
1850
i
1900
CH4 (ppbv) 50
....
....
100
,
,
,
150
•
I
,
I
,
200
,
I
250
I
,
,
I
I
300
I
•
I
•
I
350
CO (ppbv)
Fig. 8. Verticaldistributions of COandCHnovertheSchefferville, Quebec, area on August 7, 1990.
1667
HARRISS ETAL.' CO ANDCH,•OVER CANADA
(c)
ABLE 3Bcomposite altitude profiles in61rn (200 if) bins from data acquired over North Bay
ABLE 3Bcomposite altitude profiles in61m (200 ft) bins from data acquired over Schefferville + Minimum
Minimum
+Average
Average
-.- Maximum
Maximum
4
4
Ill
0
50 100 150 200 250 300 350 400 450 500
CO Concentration(ppbv)
0
,,,,I,,,,I,,,,i,•l,,,,I,,,
50
I,,
,
,
,,f,,,,
100 150 200 250 300 350 400 450 500
CO Concentration(ppbv)
(b)
(d)
ABLE 3Bcomposite altitude profiles in61m (200 ft)
ABLE 3Bcomposite altitude profiles in61m (200 ft)
bins from data acquired over Kinosheo Lake
bins from data acquired over Goose Bay
6
-,-Minimum'
-.Minimu
-.-Average
-.- Average
-.-Maximum
-.-Maximum
4
0
50 100 150 200 250 300 350 400 450 500
CO Concentration(ppbv)
0 50 100150200250300350400450500 CO Concentration(ppbv)
Fig.9. Summary statistics forthemaximum, minimum, andaverage COconcentrations measured during vertical ascents ordescents over (a)NorthBay,Ontario, (b)Kinosheo Lake,Ontario, (c)Schefferville, Quebec, and(d)Goose Bay,Labrador.
1668
HARRISS ETAL.' CO ANDCH,•OVERCANADA
(a)
(c)
ABLE 3Bcomposite altitude profiles in61m (200 ft) bins from data acquired over North Bay
ABLE 39composite altitude profiles in61m (200 ft) bins from data acquired over Schefferville
6 Minimum 5 tI"'[,-.-Maximum •:•, I-,-Average
-.-Average
5
: ---Max'.'num
4
0
' 1600
....
1650
1700
1750
1800
1850
1600
1650
CH4 Concentration(ppbv)
i
ß '
1700
'
I
i
i
1750
•
I
•
•
, .•
1800
1850
CH4 Concentration(ppbv)
(b)
(d)
ABLE 3Bcomposite altitude profiles in61m (200 ft) bins from data acquired over Kinosheo Lake
ABLE 3Bcomposite altitude profiles in61m (200 ft) bins from data acquired over Goose Bay
6 I-'-Min'irnumß
6 [--...Minimum
[-.-Average
I-
]-.-Maximum
-.-Average
5 [---'-Maximum
4
•, 4 -83 2
1
0 1600
1650
1700
1750
1800
CH4 Concentration(ppbv)
1850
0 1600
1650
1700
1750
1800
1850
CH4 Concentration (ppbv)
Fig.10. Summary statistics forthemaximum, minimum, andaverage CH4concentrations measured during vertical ascents ordescents
over(a) NorthBay,Ontario,(b) Kinosheo Lake,Ontario,(c) Scheffcrvillc, Quebec,and(d) GooseBay,Labrador
HARRISS ETAL.' CO ANDCH. OwR CANADA REFERENCES
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