Jun 20, 1981 - Other CO⢠concentration measurements in air over the Indian. Ocean (to distances of up to 450 km upwind of the coas0 produced fairly ...
JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 86, NO. C6, PAGES 5364-5372,JUNE 20, 1981
Carbon Dioxide Measurementsin Tropical EaSt African Biomes R. C. SCHNELL
Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado 80303 Air ResourcesLaboratory,Boulder,Colorado80303
g.•A. ODH InternationalMetebrological Institute,University of Stockholm,S.104 05 Sweden
L. N. NJAU KenyaMeteorological Department,Nairobi,Kenya,EastAfrica
FromJanuary1977through May 1978atmospheric CO2concentrations weremeasured hourlyand/or continuously at bimonthlyintervalsoverperiodsvaryingfrom5 to 8 daysat 10differentlocations in
Kenya, E•t Africa. During eachofthese periods, atleasttwo,andin some cases five,vertical profile
measurements of CO2 concentrations wereconductedabovedifferentbiomes.A largediurnal CO• perio-
dicitywasobserved overland,with•daytime drawdowns to 322ppmandnighttime buildups tomorethan 400ppmobserved in savannali re•ions.In andaroundtropicalrainforests, drawdowns to 310ppmand buildupsto more than 400 ppm were regularlyobserved.On the higher reachesof Mount Kenya, the
diurnalCO• cyclewasconsiderably reducedin amplitude,with variationsin the rangeof 2-6 ppm throughout the 16-month studyperiod.Onsunnydays,thedrawdown of CO• wasmeasurable to heights of at least 4000 m above groundlevel. Other CO• concentrationmeasurementsin air over the Indian Ocean(to distancesof up to 450 km upwind of the coas0producedfairly consistentconcentrations of about 328.5 ppm whiah did not fluctuatediurnally. The weekly mean CO2 concentrations over Kenya appearto havea bimodalstructure,with minimaoccurringin July and January.On the basisof the data collectedduringthe studyit appearslikely.thatregttlarobservations at a high-altitud•stationon Mount
Kenya,eitherwithflasksampling or co•ttihuous analyzer measurements, arelikelyto yielddatauseful for estimates of CO2concentration backg•bunds andtrends.Also,thereis strongevidence thatMount Kenyawouldbe a goodlocationto measurelarge-scale interhemispheric CO2 exchanges and providea uniquebase'from whichto studythe effectsof the tropicalbiomeon biogeochemical phenomena. INTRODUCTION
nuclei(CN), and turbiditylevelsbecausethe backgroundvalDuring the past decadethe scientificcommunityhas be- ues for theseparametersare fairly well established.Furthermore, such measurementscan provide information on local come aware that human activitiesmay affect the earth's clipollution as well as on how CO2 concentrations are affected matethrough increasing anthropogenic release ofg/tses and by local vegetation. The study had the following further obparticulates [Baes etal.,1977; Bach, •976].Although thecomjectives: selecting suitable locations for the monitoring site positionof the earth'satmosphereis beingmonitoredfrom a laboratories,staffhousnumberof baselinestationsaroundthe world [Watkins,1976; and supportfacilities(e.g.,workshops, Hanson, 1977;Peterson,1978],none of the stationsis located ing); estimatingcostsfor bufiding and instrumentation;and planningthe staffingand trainingof personnelto operatethe in Africa. Recognizingthe need for sucha stationin a tropical area station. The study was guided by the Scientific Advisory of Kenyanscientists, adminwhere a substantialpart of the total hemisphericexchange WorkingGroup,whichconsisted istrators, and civil servants; representatives from WMO and takes place in the northern summer [Findlater, 1969], the UNEP; and international consultants. The working group met World MeteorologicalOrganization(WMO) funded a prefeasibilitystudy [Rodhe,1975]to examinethe possibilityof regularlyto monitor the project'sprogress.Two international sitinga baselinestationin Africa. The studysuggested .that staff membersand 14 African scientistsresidentin Kenya were involved in the field work, data collection, and data Mount Kenya in Kenya might be a possiblelocation. The United Nations EnvironmentProgram (UNEP) and analysis. The field researchin the studyincludedcontinuousoperaWMO subsequently fundedthe Mount Kenya BaselineStations of Meteorology Research Incorporated (MRI) mechanition Feasibility Study, conducted from September 1976 cal weather stations measuring wind speed and direction,temthrough July 1978. The main objectiveof the study was to perature, and humidity; measurements of carbon dioxideconfind a locationin Kenyathat wasacceptable, as definedby
centrationsin air with an H. Maihak CompanyUNOR portableIR gasanalyzer;monitoringof hourlycondensation (Aitken) nucleusconcentrations with Gardner counters;collection of aerosol particulates and precipitationfor chemical [Rodhe,1975]recommended monitoringCO•, condensation
WMO [1978], such that, among other parameters,global backgroundCO• concentrationscould be monitored [Keeling et at, 1976] and trends defined. The prefeasibility study
analyses; verticalprofilemeasurements (usingaircraft)of CO•
Copyfight¸ 1981by the AmericanGeophysical Union. Paper number 80C1415. 0148-0227/81/080C- 1415501.00
and CN abovevariousareasin Kenya and over the Indian Ocean;and turbiditymeasurements with Voltz sunphotome5364
SCHNELLET AL.: CO2 MEASUREMENTSIN TROPICAL EAST AFRICA
5365
ters. Results from the CO2 measurementprogram and supporting data are presentedin this paper. MEASUREMENT
Africa
PROGRAM
AND
• Equator
METHODS
Extensive, continuous field measurements were conducted
during 11 periods of 1 week each between January 1977 and May 1978 at the sitesindicated by dots in Figure 1. In addition, CO2 and CN profilesmade by aircraft were conductedat least twice during each study period. Additional aircraft mea-
..
surements of CO: concentration were made over the Indian Ocean. On Mount Kenya, intensive studieswere conducted at stations North, East, South, West, Timau, Timau Hill, and
E•
_- _½ul•kK:nak• ßM....Kulal f/ Somali a
Jganda) Mou.tenya I /•
••be••i•s•-• •q•a • Lake•c•ria
•
•
•Watam•
..
•Mombasa •dian
Tanzania • Ocean Fig. 1. The five main study areasfor the Mount Kenya Project are each indicated by a black dot.
Low North (Figure 2). On all occasionsexcepttwo, simultaneous measurements of CO: and CN were conducted at a mini-
mum of two stationsand a maximum of four. The four highest Mount Kenya stationswere located at elevationsranging from 4267 to 4369 m; the lowest station was at 3200 m. All stations on Mount Kenya were well above the tree line in moor-
lands covered by sparsegrasstussocks5-38 cm tall between large open expansesof bare rock. Vegetation was practically nonexistent at station sites South, West, and Timau Hill.
In support of the measurementson the mountain, extra ra-
Fig. 2. Stationson Mount Kenyawhereintensivemeasurement programswereconductedand automaticweatherstationswere operatedcontinuously for at least I year (South,North, Timau Hill) and for 4 monthsor less(West,East, Timau,andLowNorth)areindicatedby blackdots.The moorlands arefreeof treesandin someareasareessentially free of any surfacevegetation.
5366
SCHNELLET AL.: CO 2 MEASUREMENTS IN TROPICALEAST AFRICA
diosonde releases were undertaken
at Nairobi
and Garissa. In
addition, numerous pibal observationswere made at sites around and on the mountain during the studyperiods.At any one time, 20-30 personnelwere usually working in the field, with equipment and samplesbeing constantlyshuttled between the samplingstationsand a central camp at the west base of Mount Kenya. Studies at sites other than Mount Kenya were conducted by fewer personnel, since logistics were so much simpler. Carbon dioxide concentrationsin air samplescollectedat 2 m above ground level (AGL) were determinedin the field by using a portable UNOR 2/200 IR gas analyzer operating on dc or ac accordingto the methodsdescribedby Bischof[1970, 1977].The sampleswere obtainedby pumpingair through 1-1 double-cockedglass flasks with battery-operatedaquarium pumps downstreamof the flasks. A minimum of 15 1 of air was pulled through a flask over a period of 5 min. The flasks were sealed at atmosphericpressure and thus were under slight vacuum when transportedto lower elevations.If the vacuum was not intact when a flask was openedfor analysis, the flask was rejected.In practice,this was a rare occurrence. For aircraft sampling,ram air from an inlet above the centerline of a twin-engine Piper Aztec was fed through the 1-1 flasks (see Bischof [1970] for aircraft CO2 sampling techniques). CN measurementsduring flights showedthat air so collectedwas free of engine combustionproducts. On four occasionsthe project staff, on board a Lockheed Electra belongingto the National Center for AtmosphericResearchof Boulder, Colorado, collectedCO,_samplesover the Indian Ocean to distancesof 450 km offshore.The aircraft operated out of Nairobi, Kenya, during June 1977 as a component of the 1977 Monsoon Experiment (MONEX). CO,_ data from MONEX flight I were found to be unreliable becauseof possibleleaks of cabin air into the collectionsystem; subsequentdata were uncontaminatedafter a speciallyfitted air intake systemwas installed for the CO,_measurements. MONEX flights2-4 operatedeastfrom Nairobi to the Kenya coast and out to sea to various distances.On MONEX flight 3, CO,_data were collectedalong the equator out to 47øE longitude. A total of 157 flask sampleswas obtained on these flights. Air samplesin the flaskswere analyzed for CO,_content between a few hoursand 3 daysafter collection.Three determinations of CO2 content were made on each flask, and the measurementshad to agreewithin 0.1 ppm CO,_concentration,or the average value of the three measurementswas not accepted.Referencegases(CO,_in air) were measuredfor every third to fifth flask. These reference gases were calibrated against secondarygas standardsmaintained at the International Meteorological Institute in Stockholm, Sweden [Bischof, 1977], and were recheckedwith these secondarystandards every 6 months.All CO,_valuesreportedhere are in the 1959 Adjusted Index Scale. During the total period of the study, the maximum relative calibration drift of the CO,_analyzer and/or referencegases was lessthan 1 ppm CO,_,and over any 6-month period the maximum drift error was less than 0.5 ppm CO,_ [Bischof, 1980]. The CO,_data were corrected for these drifts. To monitor the observers's samplingtechniqueand to add a quality control check into the CO,_ sampling and analysis while in the field, a random selectionof flasks(about one in twelve) was contaminatedby being breathedinto before they were transportedto the samplinglocation for filling. Also, oc-
casional bottles (one in forty) were prefilled with reference gasesof known CO2 concentration.The observersdid not know which bottles were pretreated, and the following CO,_ analyseswere conductedwithout earmarkingof the contaminated bottles. These controLq allowed for immediate
detection
and correctionof samplingproceduresthat did not follow the prescribedcollection plan. More than 90 individually numbered flaskswere being filled and/or analyzed in any 36-hour period during a typical intensivestudy period. Up to eight flasksper hour could be analyzedin the field. On two occasionsthe CO,_analyzerwas operatedcontinuously on battery power at a locationon the upper reachesof Mount Kenya, with referencegasesmeasuredevery 2 hours over the 5-day periods. CO2 CYCLE AROUND MOUNT KENYA
If a baselinestationis locatedat a high altitude, it is somewhat removed from the strong daily CO,_cycle that occurs during growing seasonwherever there is substantialvegetation. To confirm that a CO,_cycle existsaround Mount Kenya and to provide a reference level for comparison with CO2 measurementson the mountain, the CO,_ cycle was documented at four locations out from the mountain's base;the results are shown in Figure 3. At each of these sites,the CO2
sampleswere collected away from or above the vegetation canopy.
From Figure3 it may be seenthat a strongCO,_cyclewas observedat all four locationssampled.Naro Moru River Lodgeis 20 km westof the mountain,Mountain Lodgeis 5 km southwest,Aberdare Club is 50 km southwest,and Naivasha is 100 km west in the Great Rift Valley. Mountain Lodge is in a forested area; the other stations are in mixed
DAILY CYCLE MOUNT KENYA REGION
35
32OI-Abetdare
Club
Naiviasl•
ß
Mountain
31o ,•,1,•
Lodg• I,• I,,,I,,
,
J,•,1,,•
12 2412/1 122415/1 1224J2/2, 17.. 24 3/2 12 I 26/1 12 2427/1 12 24
!1/1
Time (LST) DcRe
Fig. 3. DiurnalCO2cyclesin theMountKenyaregionawayfrom the mountain.
SCHNELL ET AL.' CO2 MEASUREMENTS IN TROPICAL EASTAFRICA
5367 CO2 PROFILE
340
AUGUST 3 1977
CO2 CYCLE TIMAU
55
FLIGHT
HILL
MAR 7-13
0625
1978
12
- 0717
LST
50
45
33•
._--.
Hourly avcm•jes
•330 3
ß 404
1
3•a 6
0
•-394 o (0610
0727)
I
I
I
I
I
I
325
325
330
I
I
I
I
I
I
I
335
'
CO 2 Concentration (ppm)
Fig. 5. Vertical profile of CO: concentrationsupwind of Mount Kenya, 0625-0717 LST, August 3, 1977. Note that the surfaceCO: value is about 400 ppm at both takeoff and landing. ,
I
2400
•
I
2400
,
I
2400
,
I
2400
,
I
2400
,
•
2400
,
I
2400
713I 813I 913I 10/3I 11/3I 12/3I 13/3I Time (LST) DcR½
Fig. 4. CO2concentrations at 2 m abovegroundlevelat Timau Hill, March 7-13, 1978, measuredwith a continuousanalyzer and with flasksamples. The brokenlinejoinshourlyCO2valuesobtained
again, as shownin Figure 6. The vertical bars above and below each data point representthe altitude over which the sampleswere collected.On this day, fair agreementwas observed between the trend lines and data points for the aircraft and station measurements of CO,• for similar times and altitudes,
by averagingCO2concentrations from eachminuteoverthat hour. The averageCO2concentration overthe periodis 328.6ppm.
as may be seenby comparingFigures 5 and 6 with Figure 7 and Table 1. For the morning flight on August 3 (Figure 5) the differenceis 2.5 ppm or less(dependingupon where one grass-tree areas.At eachsite,a low point in CO: concentra- setsthe extrapolation),and for the afternoonflight (Figure 6) tion occursshortlyafter noonlocal time, followedby a rapid the difference is 0.3 ppm. This 2.5 ppm difference was the increaseto more than 360 ppm that persiststhroughoutthe largestobservedduringthe courseof the study.Theseparticunight hours.Apparently,in theseareas,the sunactivatesthe lar comparisonsdo not take into account differencesin CO2 photosynthesis process in the morning,andthe plantstake up concentrationsthat may have been introducedby air flowing CO•_until early afternoon,at whichtime thereis a reversalin up the mountain slopesfrom levels below the aircraft samthe cycle.This is a fairly normalpatternfor vegetatedareas pling position,which was out from the mountain proper. In [yonPaller, 1971;VermaandRosenberg, 1976;Bischof,1960], addition, from Table I it may be seen that the aircraft and althoughin the Kenya studiesthe minimum in the CO•_concentrationappearsearlier than at higherlatitudes.(Note that CO2 PROFILE the ordinatescaleof CO•_concentrationin Figure 3 is one haft AUGUST 3 1977 that of all following CO•_graphs.) 55-
FLIGHT
CO2 CYCLE ON AND UPWIND OF MOUNT
1513 -
KENYA
13 1617 LST
50
At all mountain stations,diurnal cyclesin CO•_concentra-
tions,with middayminima,wereobserved. The rangein CO•_ concentration overa day wasrarelygreaterthan 10 ppm and generallyaround4-6 ppm.Figure4 showsa representative CO•_cycleas measured both intermittently by flasksamples and continuously by a battery-operated IR CO•_analyzeron site.The dotsconnectedwith broken linesare hourly CO•_val-
--E
40
=
35-
30-
uesobtainedby averagingthe minuteCO•_values.The dots connectedwith solidlines are hourly spotvaluesof CO•_con-
25-
centrations. This cyclewastypicalfor all stationsin all seasonson Mount Kenya.
A typicalearlymorningverticalprofileof CO•_concentration upwindof andaboveTimau Hill (3897m) exhibitshigh concentrationsof CO•_at and near the surfaceand lower con-
AIRPORT .
.,
1513
20-
325
LEVEL
>..
1617
330
3 5
3 0
CO2 Concentration (ppm)
centrations at higheraltitudes,asshownin Figure5. By 1000 Fig. 6. Vertical profile of CO2 concentrationsupwind of Mount local standardtime (LST) suchhigh surfaceCO•_concentraKenya, 1513-1617 LST, August 3, 1977.The high surfaceconcentrationswerealwaysreducedto nearthe valuesobservedat up- tion of around 400 ppm measuredin the morning of the same day
perlevels,andby 1200LST exhibited a 3-10ppmdrawdown. By 1600LST neargroundlevel,CO•_concentrations increased
(Figure 5) has been reducedto about 326 ppm by 1513 LST and recoveredto 330 ppm by 1617 LST.
5368
SCHNELLET AL.: CO 2 MEASUREMENTSIN TROPICAL EAST AFRICA
TABLE 1. ComparisonsBetween the CO2 ConcentrationsObserved in Flask SamplesCollected on Timau Hill and Flask SamplesCollectedWith an Aircraft Flying Upwind of Mount Kenya Timau
Hill
Aircraft
Time, LST
CO2, ppmv
CO2, ppmv
Time, LST
Altitude, m
Aug. 3, 1977
0700 0800 1600 1700 1900 0600 0600 0700 1600
331.3 331.3 326.2 325.4 325.5 329.2 329.7 328.6 329.8
Jan. 12, 1978
0800
327.0
Jan. 15, 1978
0800 1000 1600 1800 0600 0800 1600 1000
330.4 327.4 325.3 327.2 331.6 331.6 329.8 329.7
331.3 332.4 326.7 323.0 325.1 327.2 327.2 327.5 329.5 329.5 329.5 327.0 328.3 329.3 329.9 327.5
0728-31 0731-34 1654-57 1742-48 1818-24 0634-37 0634-37 0706-09 1543-46 1545-52 1558-01 0808-11 0811-14 0938-41 0945-49 1600-04
3352-3688 3688-4023 3• •.114 3169-4267 4267-3169 3505-3962 3505-3962 4053-3352 3840-4389 3230-3779 3413-3108 3352-3657 3657-3962 3566-3779 3779-4236 3505-3779
333.1
0733-37
3148-3840
330.4 329.9
1633-36 1003-06
4206-4511 3292-3779
Date June 9, 1977
June 12, 1977 June 13, 1977
Aug. 3, 1977
Jan. 15, 1978
March 9, 1978 March 10, 1978 March 12, 1978
For the aircraft samples,the time period of the flaskexposureand the rangeof altitude over which the sampleswerecollectedare presentedfor flaskswith the closestcomparabletimesand altitudesto thoseof the samplestaken at Timau Hill.
Mount Kenya groundstationmeasurements differ by 0.5 ppm or lesson 9 out of 19 comparisons.On two occasionsthere is exact agreement.
During the main monsoomseason(approximatelyNorthem Hemisphere late spring) the fluctuationsin the vertical CO•_profile were larger than during the rest of the year, as shownin an afternoonprofile for June 12, 1977(Figure 8). In this case, both the daytime drawdown and the nighttime buildup of CO2 concentrationsextended to an altitude of at least 4500 m AGL, which may be a reflectionof strongvertical mixing of surfaceair associatedwith the convectivemonsooncumulusclouds.About 20% of the vertical CO2 profiles measuredduring the project exhibiteda similar large vertical change.Sincethe vertical profileswere generallyconductedat distancesfrom 10 to 20 km upwind of the central peak area, it is suggestedthat this uneven mixing was widespreadand not the result of upslopeor turbulenceeffectsintroducedby the isolatedmountain itself. Implicit in theseresultsis the suggestion that during these particular periods the vertical atmo-
measured up to 5 km offshorewhenoffshorewindscarriedair influencedby coastalvegetationout to sea.During steadyonshorewind events,the CO2 profilewas relativelyconstantin the vertical(as observedin Figure 10) from sealevel up to at 340
CO2 CYCLE STATION
TIMAU
AUGUST
2-
8
HILL 1977
335
330
sphericCO2exchangeis occurringin convectivebubbles. 325:
The resultsof atmosphericCO2 measurementsover eastern Kenya and the Indian Ocean are shown in Figure 9 for a night MONEX flight on June 29, 1977.The resultsfrom this and from daytime flightsshowedthat the CO2 concentrations over the oceanwere relatively constantat all levelswhen com, I , I , I i I , I , I , 2400 2400 2400 2400 2400 2400 pared to measurementsover land. When all the over-ocean MONEX measurements were taken together(10 days) they l•rn½ (LST) Date produceda mean of 328.67ppm, a standarddeviationof 0.87 ppm, and a standard deviation of the mean of 0.040 ppm Fig. 7. CO2 concentrations measuredat 2 m abovegroundat [Tryon and Caldwell, 1980]. Vertical profilesof CO2 concen- Timau Hill August2-8 1977,with flasksamples.The surfacemeamayberelatedto theairborne measurements presented in tration measuredover the oceanjust offshoreindicated that surement• of two pointsat the samehour the CO2 profile was relativelyconstantin the vertical above Figures5 and6. Verticalseparation I
showsthe data spreadfor two separateflasksexposed10 min apart
the lowest 100m, as may be seenfor a typical caseillustrated beforeand after the hour. The averageof the two flasksis usedto proin Figure 10. Within the lowest 100 m, a large perturbation ducethe trend lines.The averageCO2 concentrationover the period (increaseor decrease)in CO2 concentrationwas occasionally is 328.7 ppm.
SCHNELLET AL.: CO2 MEASUREMENTSIN TROPICAL EAST AFRICA
1645
co2 PROFILE
.
JUNE 11 1977 FLIGHT
5369
9
SEPTEMBER 221977 FLIGHT
- 1730 LST
0700
17
- 0800
LST
45 o
0
30
--'
25
._
•
20
25-
20ß
IS4S
i
I,, 17•0
i
I
,
!
i
i
i
i
i
!
i
i
CO2Ccx'K:entr•tion (ppm)
' 3•5" ' "
330
335
CO2 Cor•ntmtion (ppm)
Fig. 8. Verticalprofileof CO2 concentrations on the afternoonof
June11,1977.CO2drawdown through a layersome3000m deepisin
Fig. 10. Verticalprofileof CO2concentrations overth8near-shore
evidence,asis the 6 ppm increase in CO2concentration at 2 m above groundlevel between1645 and 1730 LST, measuredat takeoff and landing.CO2 concentrations are plottedat the centerof the altitude rangeoverwhichthe flaskswereexposed.The trendline indicatesthe ascentportionof the flight,whichoccurredat a differentlocationthan
environment of theIndianOceanoff Watamu, KenY• 0700-0800 LST, September22, 1977.The high CO2 concentrations in the air nearthe surfacesuggest thatit wasrecentlyassociated with a nocturnal buildupof CO2 overland that had beenadvectedout to sea.
the descentportion.
least5000 m abovesealevel (top of sounding)when compared with similar measurementstaken around Mount Kenyaß
region a month earlier) representthe true state of the CO2
concentration in the lowertroposphere in the Garissaarea in that seasonof the yearßUnfortunately,there are no CO2 mea-
Measurements of the CO2cycleat Garissa(138m abovesea level, 300 km inland), located in a low-biomass,semidesert scrublandareain a regionof leveltopographyin northeastern Kenya, providedsomeinterestingresults.For instance,concentrations
measured
at 6 m above the surface exhibited
surements upwindof Garissaoverthe IndianOceanavailable for thisperiod;thusthe possibilitythat theserelativelyhigher CO2 concentrations are an artifact of upwind vegetationef-
a
fectsshould not be discountedat this time. Also, sincethese
strong,persistentdiurnal cycle with daytime drawdownsto 323 ppm and nighttime buildupsto more than 370 ppm. The effectsof this cyclecouldbe measuredverticallyup to 2500 m AGL, as shownin Figure 11. No convectivecloudswere observed in the region during this sounding,and winds at all flight levelswere from the southeast.Also in Figure 11, it may
measurements wereconducted duringa rainy season, the resultsmaynotberepresentative of all timesof theyearin semidesert and desert areasß DISCUSSION
At the outset of this project we hypothesizedthat non-
be observed that,at altitudesabove2500m, CO2concentra- fluctuating,steadystate'backgroundconcentrationsof CO2 tionswere essentiallyconstantat around 335 ppm. Sincethere are no largeanthropogenic sourcesof CO2 upwindof Garissa to the coast and over the Indian Ocean, it might be argued that theserelativelyhigh CO• concentrations (comparedwith concentrationsof 328-330 ppm observedin the Mount Kenya
would be measuredfor someperiodsof the day on Mount Kenya or over other continentalareas.This wasnot the case,
sincea diurnalCO2cyclewasobservedon all dayssampled. The next task was to determinewhetherthe diurnal cycles
contained information on background CO2concentrations
40-
ß33o.4
35-
.32•.9
MONEX
ß333.o
4
JUNE 29 1977
ß 329.1
50'
0
o 25-
•
'• 2o..•
329.5,,329.3 1800-- 2400 LST
i1•HIlls
/•
I I.
A
/ \
'328.6 ß328.9 .3,o.,
'
.3:•o. 6 .:•28.•
..•.4
ø328'7
.,•.3 ..o.,,.3..7 ß
4.-
