Overview of an Aircraft Expedition Into the Brazilian Cerrado for the Observation of Atmospheric Trace Gases

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 101, NO. D19, PAGES 23,973-23,981, OCTOBER 30, 1996

Overview of an aircraft expedition into the Brazilian cerrado for the observation of atmospheric trace gases

V. W. J. H. Kirchhoff and P. C. Alvalfi Instituto Nacional de PesquisasEspaciais, S5o Paulo, Brazil

Abstract. Tropospherictrace gaseswere measuredfrom an aircraft platform. The flights were organizedto sampleair massesfrom the geographicarea of central Brazil, where the vegetation,a savanna-typeenvironment with the local name of "cerrado",is subjectto burningevery year, especiallythrough August, September,and October. These measurements were made as a Brazilian local contribution to the international field campaignorganized by NASA, the Transport and AtmosphericChemistry Near the Equator-Atlantic (TRACE A) mission,and the SouthernAfrican Fire Atmospheric ResearchInitiative (SAFARI). The major NASA TRACE A missionused the NASA DC 8 aircraft, with most flightsover the South Atlantic Ocean region. In Brazil, missionsusing small aircraft measuredozone and carbon dioxide continuously,and carbon monoxide, nitrous oxide, and methane usinggrab sampling.In addition, ground-basedmeasurements were made continuouslyover most of the dry monthsof 1992, and ozonesondeswere launchedat three different sites.Geostationary Operational Environment Satellite-East (GOES E) imagesand a specialnetwork of radio soundingsprovided meteorological information,and advancedvery high resolutionradiometer (AVHRR) imagesindicated the distributionof fire pixelsin the region of interest. Most of the biomassburning in 1992 occurredin the state of Tocantins,with about 22% of all the burning in Brazil. The state of Mato Grossowas second,with 19% of all burning. The Brazilian aircraft was used mostlyin these two states,near the cities of Porto Nacional and Cuiabfi, for in situ sampling;31 vertical profileswere made in air massesconsidered to be well mixed, that is, not in fresh plumes.Although the major interestwas the dry season,sampling was also made during the previouswet seasonperiod in April 1992 for comparison;10 vertical profileswere obtainedusing the same aircraft and measurementtechniques. There is a clear differencebetween these two oppositeseasonal periods, most evidentin the 03 and CO data. Both Cuiabfi and Porto Nacional show some30-60 parts per billion by volume (ppbv) larger methaneconcentrations, for example,during the dry season,in comparison to the wet season,the differenceat Cuiabfi being larger. The methane data for the wet seasonshow no significantdifferences between Cuiabfi and Porto Nacional mixing ratios, which seemsto excludethe existenceof significantsources or sinksat these sites during this wet season.The ozone mixing ratios vary around 15 _+5 ppbv in the wet season,and from a minimum of 35 to a maximumof 70 _+ 10 ppbv, dependingon height, in the dry season.The largestvariability is seen in the carbon monoxidemixing ratios which vary from 90-100 ppbv in the wet seasonto maxima of 300 at 3.3 km and 600 ppbv at 1.2 km height in the dry season.

Introduction were immediatelyburned to clear the land. Deforestationrates thenwere about 20,000 km 2 yr-•. Presently,federal incentives Biomass Burning are no longer in effect and the migrations have decreased Brazil is one of the tropical countriesthat still has a large considerably.Although there is still significantdeforestation populationgrowth rate; its populationhas doubledin the last estimatedat about10,000 km 2 yr-• by 1995,the deforestation 50 years.This causespressure to searchfor new land, modu- trend has been decreasingconsistently over the last 7 years. lated by the country'seconomic situation. Years ago the fed- Most of the biomassburning has turned to the savanna-type eral governmentof Brazil created incentivesfor people to environments, known as the cerrado of central Brazil. Biomass move especiallyfrom the poor northeaststates to the Amazo- burningin Brazil has a strongseasonal cycle (from wet to dry, nian states,for basic development.This causedconsiderable or vice versa) with almost no burning from Januaryto May, populationmigrations, with large rates of deforestation,espe- and strongburning activity in July to October. For September cially in the state of Rondonia, and the south of Parfi, well of 1992, for example,it is shownthat 22% of all burning in documentedby the press. Forest land became pasture and Brazil occurred in the state of Tocantins. The definition of wet several new cities were created. Much of the deforested areas and dry seasonsis generally subjective,but can be defined Copyright1996 by the American GeophysicalUnion. quantitativelyas shownby Kirchhoffet al. [1992]. Paper number 95JD03029. Biomass burning introduces several gases into the lower 0148-0227/96/95JD-03029509.00 atmospheremodifying its natural composition[Crutzen et al.,

23,973 23,974 KIRCHHOFFAND ALVAL*: AIRCRAFT EXPEDITION IN BRAZIL

Table 1. Flight Locations,Types and Data ObtainedDuring Major TRACE A Mission Period (Dry Season,Total of 31 Aircraft Profiles) Flight Flight Type and September,1992 Location Sites* Number Data Obtained

8 SJC-CBA transit 1 03, CO, N20 , CO 2 9 CBA 1, 2 profiles1, 2 03, CO, N20 , CO2, CH 4 10 CBA 3, 4 profiles3, 4 03, CO, N20 , CO2, CH 4 13 CBA 5 profile 25 03, CO, N20 , CO2, CH 4 15 CBA-PN 7 profile 5 03, CO, N20 , CO2, CH 4 16 PN 10, 11 profiles6, 7 03, CO, N20 , CO2, CH 4 17 BG 5 profile 8 03, CO, N20 , CH 4 18 PN 8 profile 9 03, CO, N20 , CH 4 19 PN 9, 8, 9 profile 10, 11, 12 03, CO, N20 , CH 4 20 PN 7, 10, 12 profile 13, 14, 15 03, CO, N20 , CO2, CH 4 21 PN 7, 10, 12 profile 16, 17, 18 03, CO, N20 , CO2, CH 4 22 PN 7, 10, 11 profile 19, 20, 21 03, CO, N20 , CO2, CH 4 23 PN 7, 10, 12 profile 22, 23, 24 03, CO, N20 , CO2, CH 4 26 SJC-PN transit 2 03 27 PN-AF 7, 6 profiles26, 27 03, CO, N20 , CH 4 28 PN 7, 10, 12 profile 28, 29, 30 03, CO, N20 , CH 4 29 PN 11 profile 31 03, CO, N20, CH 4

*These refer to flight sitesshown in Figure 5 Most flightsare madebetween 1000 LT and 1400LT. Locationshorts are as follows:S•o Jos6dos Campos,SJC; Cuiabgt, CBA; PortoNacional, PN; Barra do Gar•as,BG; Alta Floresta,AF.

1979]. This fundamentalconcept has receivedincreasing at- and Brazil [Fishmanet al., this issue]and, in addition,field tention,both from a purely theoretical(photochemical) per- missionswere organizedin Africa and Brazil by independent spective[Jacob and Wofsy,1988; Logan, 1985] as well as from groups.A groupfrom Europeworked in Africaunder the South- the observationalpoint of view. A number of new observa- ern AfricaFire AtmosphericResearch Initiative (SAFARI), and tional groups developedfacilities to measureatmospheric in Brazil the InstitutoNacional de PesquisasEspaciais (INPE) tracegases [Cros et al., 1987,1988; Kirchhoff et al., 1989;Kirch- grouporganized special ground-based work andtwo aircraftmis- hoff and Marinho, 1990] and severalfield expeditionswere sionsdescribed in this report. organizedto measurethese effects in the tropics,using aircraft [Crutzenet al., 1985;Delany et al., 1985;Gregory et al., 1988; The Brazilian Componentof TRACE A Browellet al., 1988, 1990;Andreae et al., 1992;Anderson et al., Two aircraftexperiments were organizedin 1992,one in the 1993;Hoell et al., 1993;Andreae et al., 1994].In the late 1980s, wet seasonand one in the dry season.In addition, ground- J. Fishmanand coworkersdeveloped a new techniqueto study basedobservations were made at Cuiabfi(16 ø S, 56ø W), Porto troposphericozone distributionsfrom simultaneousobserva- Nacional(10.5 ø S, 48ø W), and Natal (6ø S, 35ø W). For the tions of two satellites,and thesestudies detected a large ozone major dry seasonmission, aircraft flightswere organizedini- bulge in the South Atlantic Ocean, near the African coast tially such that the timing would correspondto the major [Fishmanet al., 1990, 1991; Watsonet al., 1990].Preliminary NASA TRACE A campaign,but technicalproblems with the studiesat Natal, for example[Kirchhoff and Nobre, 1986] and NASA DC 8 causeddelays and changed the originalplans. The later for the South Atlantic by J. Fishman and coworkers, Brazilian aircraft flights are shownin Table 1. Most of the indicatedthat this large ozone bulge could be the result of actual sitesfor profilingwere locatedclose to Cuiabfi in the transportand chemistryinduced by biomassburning in the state of Mato Grosso, and near Porto Nacional in the state of nearby South American and African regions.This early hy- Tocantins(see Figure 5). Thesesites are part of the cerrado pothesiswas confirmed by this specialfield mission.Not only environment, but Cuiabfi has the influence of the rain forest are the sourceregions in Brazil andAfrica strongand efficient area to the north andwest, and possiblyfrom the Pantanalarea enoughfor the chemicalproduction [Jacob et al., this issue; in the south-southwest.Thus the fuel type beingburnt is grass, Pickeringet al., thisissue] but alsodetailed trajectory analyses shrubs,and small trees, with flaming combustionprevailing [Fuelberget al., this issue]show that the Brazilian sources over smoldering.However, when the winds blow from the contributeto the South Atlantic tropical portion of the ozone forest areas,near Cuiabfi,there may be a significantcontribu- bulgeat the higherlevels, above about 500 hPa, whereasthe tion from smolderingfires. Most of the new fires are lit in the lowerportions of the tropospherein the SouthAtlantic region, afternoon, around 1500 to 1600 LT, and they usuallylast for from coastto coast,receive the burningproducts from Africa about 1 to 2 hours,depending on the local fuels. Some smol- [seealso Thompson et al., this issue]. deringgoes on duringthe night,but by the morningof the next day the fires disappearedand what is left is a rather uniform The TRACE A Mission smoglike-filled atmosphere. From the aircraft, at certain A largefield campaignwith a strongfocus on international heightsnear 2 km where stronginversions are common,the cooperation ancl participation was organized by NASA's visibi!i• is normally,qo bad that the horizoncannot be seen. Global TroposphericExperiment (GTE) program,and was Previous INPE Measurements called the Transport and AtmosphericChemistry Near the Equator-Atlantic(TRACE A) experiment.The NASA DC 8 The INPE grouphas made groundobservations of 03 and was programedto fly over the SouthAtlantic region,Africa, CO at Cuiabfifor severalyears [Kirchhoffand Rasmussen, 1990; KIRCHHOFF AND ALVAL•: AIRCRAFT EXPEDITION IN BRAZIL 23,975

Kirchhoffet al., 1992; Kirchhoffand Marinho, 1994], and a long-termprogram for obtainingozonesonde data at Natal, in collaborationwith NASA, has investigated,for example,the possibleinfluence from biomassburning in Africa [Kirchhoff and Nobre, 1986;Logan and Kirchhoff,1986]. As mentioned, thiswas again a major issueof TRACE A. A specialreport on ozone observations,ground based and using sondes,during TRACE A, is presentedin a companionpaper [Kirchhoffet al., this issue]. Also more recently,greenhouse gases have been measured in Brazil. Previouswork on atmosphericmethane has shown that floodedareas act as methanesources, injecting significant fluxes of methane into the atmosphere[Bartlett and Harris, 1993]. There are severallarge flooded areas in Brazil. The largestnatural areasare probablythe Amazon River complex, in the Brazilian statesof Amazonia and Parfi, and the Pantanal area in the statesof Mato Grosso,and Mato Grossodo Sul (a significantpart extendinginto Boliviaand Paraguay).In addition to these, there are also many artificially created flooded areas for the generation of electricity. Besides the flooded areas as potential sourcesto increaseatmospheric methane concentrations in Brazil, there is another methane source ac- tive in the dry seasonof central Brazil, which is biomassburning [Jacoband Wofsy,1988, 1990;GoMammer, 1991; Levine et al., 1991].The instrumentfor methanemeasurements has been describedby Oliveiraet al. [1993].

Objective of Present Work The objectiveof this work is to describean overviewof the INPE Bandeiranteaircraft mission that took placein April and Septemberof 1992 in the Brazilian cerrado region of central Brazil. Highlight observationsare reported of the atmospheric trace gasesmethane, nitrous oxide, carbon dioxide, carbon monoxide, and ozone, their concentrations and variations in the lower troposphere(below 5 km) during the NASA GTE/ TRACE A mission. Specificobjectives are as follows:(1) obtain representative and averagemixing ratios of trace gasesin wet and dry season periods,in the remotebiomass burning areas of centralBrazil; (2) comparewet seasonand dry seasonmixing ratios; (3) observethe spatialdistribution of carbondioxide, and compare mixingratios over savanna and overforests; (4) investigateand Figure 1. External characteristicsof the INPE Bandeirante aircraft used for obtaining in situ samplesof trace gasesin comparesources for methaneand nitrous oxide; and (5) cor- Brazil during the TRACE-A mission. Three positions are relate precipitationand fire pixelsto measuredtrace gases. shown:from the side, top, and front. This work considersitems (1) and (2) aboveand other fol- lowing papers consider the remaining items. A companion paper describesthe ozone soundingsthat were made during normal use to below about 4-5 km. For specialrequirements, TRACE A [Kirchhoffet al., this issue].In addition,a second oxygenmasks are availablefor crew and operators,but its use independentBrazilian aircraft missionthat measuredradon, is generallyavoided. soot carbon, and aerosolswill be describedelsewhere. Flight Patterns Figure 3 describesthe generalflight patternsused by the Experiment INPE aircraft. Basically,three different approachesare fol- Aircraft lowed, dependingon the objectivesof flight. For obtaining The INPE aircraftis a two engineBandeirante, model EMB vertical profiles,the pattern of Figure 3a is often used.At a 110. It has increasinglybeen used for obtainingin situ mea- fixedgiven height, as previously determined, the pilot fliesinto surementsof atmospherictrace gases,but has alsobeen used the prevailingwind. The flight leg at any given height takes for aerophotogrammetry.The aircraft is shown in Figure 1 about 10 min, which is generallyenough for obtainingall the (externalview in three positions:side, top, and front) and parametersthat are measured.In caseof large variabilityor Figure 2 (internal view from the side and top, and positionof other problems,another leg at the same height may be con- someof its instruments).Its total length is 14.79 m. The pas- sidered,and this is in generalflown along the wind direction. sengerseats can be removedas needed. One of the shortcom- The redundancyleg, shownin Figure 3b, is usedwhen the real ingsof this facility is that it is not pressurized,which limits its time instrumentation shows results that are unusual or when 23,976 KIRCHHOFFAND ALVAL,•: AIRCRAFT EXPEDITION IN BRAZIL

the cansfor only short time periods,in general not more than about a week. For the aircraft work, the cansare filled in flight by specialair pumps,to a pressureof about 30 psi, a procedure that takes about 2 to 3 min at selected height levels. The samplesof this report were obtained in the biomassburning CAMERA OPENINGS area of central Brazil, especiallynear Cuiab•t and Porto Na- cional. The accuracyof the chromatographicmeasurements depends on the standardsused, provided by other international laboratories,and the precision is 0.6% for methane, 0.5% for nitrous oxide, and 0.2% for carbon monoxide. Ozone and carbon dioxide have been measured continuously.For ozone the UV absorptiontechnique is used which / providesmeasurements at about 15-sintervals. This technique RACK hasbeen widely usedfor manyyears and resultsof it havebeen describedin considerabledetail in the literature. The accuracy Figure 2. Internal view of the Bandeirante aircraft, in two positions:side and top views. of the measurementsis tested or adjustedat regular intervals, generally a year, by comparisonwith international standards, and the precisionis nearly 2 or 3 ppbv. The carbon dioxide the operatorshave trouble. Finally, the option shownin Figure measurementsuse the techniqueof nondispersiveinfrared ab- 3c is usedwhen a spatial surveyis made at fixed height. sorption,and provideobservations at about 10-sintervals. This technique has recently achieved excellent performance, pro- Instruments and Methods viding reliable observationsand small sizeinstrumentation that Methane, nitrous oxide, and carbon monoxide concentra- can be easily carried to the field or set up on towers and aircraft. tions in air were measuredby gas chromatography.The first methaneobservations by the INPE group,as well as a descrip- Atmospheric Conditions tion of the measurementfacility, were presentedby Oliveiraet The Cuiabfi site had much higher precipitation rates in Sep- al. [1993], describingthe column arrangementof the gaschro- tember and October 1992 than one would expect,on the basis matographand the flame ionization detector (FID). The ni- of its climatologicalmean. This is shown in the companion trousoxide chromatography was developedby Marinho [1993], paper, Figure 2 of Kirchhoffet al. [this issue].The data for usingbasic chromatographic separation with a Porapak-qcol- Cuiabfi (and Goifinia) clearlyshow that in September1992 the umn, operatedat 50øC,and ElectronCapture Detector (ECD) precipitation intensitywas about 3 times as large as the "cli- detection.Kirchhoff and Marinho [1990] describedthe carbon matological" average. For October the precipitation amount monoxideinstrumentation, which usesa chromatographicsep- was also considerablylarger than the average. Evidently, the arator followed by a mercury oxide detector. The measurementsare made in our laboratoryin SgoJos6, dos Campos,Sgo Paulo, Brazil. For these long-lived gases,grab samples are collectedin specialstainless steel flasks,internally electropol- ished,by a method developedby R. Rasmussen.The 800-mL cans are handled accordingto international standards,being evacuatedimmediately after analysis.The samplesare kept in

a) Profile Leg b) RedundancyLeg

_J•eference,,•, 10Km//) Wind• - •) Reference ) Wind tt tOKm

c) Survey Flight

Figure 3. Typical flight paths used in the September 1992 mission.In a, a profile leg is made into or along the wind Figure 4. GOES E satellite image in the infrared, showing direction and has typicallya length of 10 km, or less.In case the strongcold front that was almost stationaryover the con- there are difficulties,the operator may choosea redundancy tinent reachingover to Cuiab• (which receivedmuch larger leg, as in b; a and b legsmay be stackedup to obtain vertical precipitationrates than its climatologicalmean) but not as far profiles;another option that has been usedis the surveyflight as Porto Nacional, in the state of Tocantins(which received in which a large area is coveredat the same height, as in c. lessrain in Septemberthan its climatologicalmean). KIRCHHOFFAND ALVAL•: AIRCRAFTEXPEDITION IN BRAZIL 23,977 high precipitationrates in Septemberand October 1992 at Table 2. Flight Locations,Dates, and Data Obtained Cuiabfi (and Goifinia) affectedthe overall resultsin terms of During Wet SeasonPeriod (Total of 10 Aircraft Profiles) biomass burning intensity in the region, and the aircraft April Flight Flight Data avoidedthis part of the savanna,concentrating its effortsnear 1992 Location Site* Type Obtained Porto Nacional. It is noteworthythat the months of July and August 1992 were effectivelyvery dry monthsat Cuiabfi (and 1 GO A profile 03, CO, N20, CH 4 Goifinia), contraryto Septemberand October. 2, 2 GO A, B profiles 03, CO, N20 , CH 4 3 CBA C profile 03, CO, N20 , CH 4 The station Porto Nacional, contrary to what occurred at 4, 4 CBA C, D profiles 03, CO, N20 , CH 4 Cuiabfi,was quite dry duringSeptember 1992. The strongcold 5 PN E profile 03, CO, N20 , CH 4 frontsthat were ableto reachCuiabfi (and Goifinia) dissipated 6, 6 PN E, F profiles 03, CO, N20 , CH 4 before they could propagateas far north as Porto Nacional, 7 GO A profile 03, CO, N20 , CH 4 leaving the precipitationrate for September at slightlyless *These refer to flight sitesshown in Figure 5 than one half of the "climatological"mean, defined with an Location shorts are as follows: Goifinia, GO; Cuiabfi, CBA; Porto 11-year data sequenceavailable from 1977 to 1987 (see the Nacional, PN. companionpaper for details).In a period of 1 year, one may notice a very long dry period, of almost5 months,when precipitation amountsto lessthan 50-mm per month, but which Grosso(MT, 19%), Parfi (PA, 13%), Maranhao (MA, 12%), hasless than 10-mmper month in at least 3 monthsof this dry and then Goifis (GO, 8%). Thus the profilesdescribed in this period. Also, the transition time between wet (300-mm per aircraft missionwere obtainedin the geographicalarea where month) and dry periodsis rather short (about 1 month). most of the biomassburning was taking place. Examination of several satellite images show an almost cloudlesspanorama over central Brazil during the dry August- Overview of Measurement Results Septemberperiod in the Brazilian cerrado.This was also the Ozone case for 1992 during August but in September cold fronts advancedfrom the southwestas far as Cuiabfi,but not reaching The ozone measurementsare summarizedin Figure 7 show- Porto Nacional, as can be seen for example,in the GOES E ing the wet and dry seasonaverages, minima and maxima.As image for September15, 1992, at 16 UT, shownin Figure 4. mentioned,the data reflectresults for an aged(generally about Note that the stateof Tocantinsis essentiallycloudless on this 24 hours)and mixed air mass,a characteristicthat canbe easily day, and on most of the observationdays in September. identifiedby the nakedeye. Open firesand freshsmoke plumes were avoided,since the objectiveof the flightswas to obtain a Satellite Observation of Fires characterizationof the mixed atmosphere.The flight times of Figure 5 showsthe approximatelocation of the sites over most of the profileswas near local noon, when dry convection which most of the flightswere made, as listed in Tables 1 and activity is largest, providing generally good mixing of the at- 2. Figure 6 showsthe largestfire percentagesin a sequential mosphere.On most occasions,mixed conditionsin one height way. The sequenceby state is Tocantins (TO, 22%), Mato

24 , I , I , I , I , I , I , I , I , I , I , TO I I I

z O 20 MT - =• SEPTEMBER 1992 _

i- 16 - z o o PA

o i- -15 o 8- GoBA -20 z

SEPTEMBER 1992 n,, RO -25

-3O 0 ' I'l'l'l'l'l'l'l'l'l' 0 1 2 3 4 5 6 7 8 9 10 11 -70 .65 -60 -55 -50 -45 -40 -35 CONTRIBUTION BY STATE LONGITUDE Figure 6. Sequentialdecrease in the percentageof total fire Figure 5. Map of Brazil showingmost of the aircraft sites countsper state for Brazil, in September1992. The figuresare where profiles have been made. Also shownare the percent- respectivelyfor the statesof Tocantins(TO), Mato Grosso agesof the total numberof fires detectedby NOAA AVHRR, (MT), Parfi (PA), Maranhgo(MA), Goifis(GO), Bahia (BA), per state, during the period of this experiment.The Brazilian Piaui (PI), Rond6nia (RO), and Mato Grossodo Sul (MS). statesmost affectedare Tocantins(TO), Mato Grosso(MT), The unlabeledbar representsthe contributionof the rest of the where most of the flightswere made. states. 23,978 KIRCHHOFFAND ALVAL•: AIRCRAFTEXPEDITION IN BRAZIL

5 ' I ' I ' I ' I ' I ' I ' I ' I ' I ' i I I I ' I ' I I I ' I

SAVANNA AIRCRAFT TRACE-A BRAZIL- 1992 PROFILES 4 I .

WET DRY WET DRY

0 0 ' I ' I ' I ' I ' I ' I ' I ' I ' I ' ' I ' I ' I ' I ' I ' I ' 0 10 20 30 40 50 60 70 80 90 100 0 100 200 300 400 500 600 700 O3 MIXING RATIO ( ppbv ) CO MIXING RATIO ( ppbv ) Figure 7. Averages,maximum and minimum plot for ozone Figure 8. Averages,maximum and minimumplot for carbon mixing ratios for wet and dry seasonexperiments, 1992. monoxide mixing ratios for wet and dry seasonexperiments, 1992. level alsomeant sameconditions in the other heightlevels. The clear distinction between the wet and dry seasonresults is a Nitrous Oxide confirmation of previous results of ozone measurementsin biomassburning regions [Kirchhoffand Rasmussen,1990; An- The effect of biomassburning on nitrous oxide seemsto be dreaeet al., 1992, 1994;Jacob, this issue]. small,in comparisonto ozone and carbonmonoxide. Figure 9 The absolutevalues of the ozone averageconcentrations in showsthe variabilityof the mixingratio of this gas,from about Figure 7 seem to be lower than the ozone concentrations 310 to lessthan 320 ppbv(only 10 ppbvin 310, or 3 %). The dry observedby other techniques,but the reason for the differ- seasonaverages are slightlylarger than the wet seasonaver- encesmay be largelydue to the differentsampling procedures. ages,but within the standarddeviations of the mean (not In the aircraft experimentone was lookingfor a mixed atmo- shownin Figure 9). sphereto obtain observationsthat could be comparedwith a wet seasonaverage. For the ozonesondelaunches a very spe- cific airmassis being sampled.Thus, occasionally,large ozone concentrationswere observed,for example,at Porto Nacional where near the ground concentrationsof 80 ppbv were seen [Kirchhoffet al., this issue].

Carbon Monoxide • The CO measurementswith an overall average,minima and maxima,are summarizedin Figure 8. The measurementsshow a distinct separationof the wet seasonresults and the much larger dry seasonconcentrations, which may be larger by factors of from 4 to 6. This result for the abovegroundatmosphere is also in agreementwith previousresults for ground-based measurements[Kirchhoff et al., 1989;Kirchhoff and Rasmussen, 1990].In the dry season,the presentdata indicatea CO mixing ratio decreasingwith height. This seemsto be a natural con- sequence,since the CO is the result of the direct injectionfrom fires,especially in the smolderingcombustion stage, where the source is directly on the ground. In the wet seasonthe CO profile has no strongsource at the ground, and the mixing in the atmosphereis stronger,which givesthe profile an almost constantmixing ratio. The dry seasonCO may be 3 times as large as the wet seasontypical value of about 100 ppbv,at the 305 3!0 315 320 3_>5 lower height level of 1 km, but valueslarger than a factor of 6 have also been observed. It should be added that observations N20( ppbv ) in 1990, alsoin the cerradoarea, gaveeven larger CO concen- Figure 9. Mass plot of nitrous oxide mixing ratio obtained trations, in which CO reached a mixing ratio of 1000 ppbv. duringthe experimentin 1992 (not all data is shown). KIRCHHOFFAND ALVAL•: AIRCRAFT EXPEDITION IN BRAZIL 23,979

i I [ I ] I I Porto Nacional. Both panelsshow larger concentrationsin the dry season.Contrary to the ozone and carbon monoxide data, C02 there are no other databaseswith which the nitrous oxide, the carbon dioxide, and the methane may be compared. The larger concentrationsof methaneobserved near 1.8 km at Cuiabfi (Figure 11) are probably the result of sampling inside an inversionlayer that is often formed near this height, produced by dynamic vertical motions in the lower atmosphere,as previouslydescribed for ozone observations[Kirch- hoffandMarinho, 1994].Another apparentfeature in Figure 11 is that methane concentrations at Porto Nacional and Cuiabfi are significantlylarger duringthe dry season.This confirmsthe general idea that during the dry season,biomass burning is responsiblefor an increaseof methane concentrationsin the environment;in this caseby about 40 ppbv. Larger concentrations at Cuiabfi relative to Porto Nacional may be causedby a larger smolderingcombustion component near Cuiab• [Griffith et al., 1991]. A closerinspection of Figure 11 showsthat there is no significantdifference in the methane mixing ratios at Cuiabfi and Porto Nacional, during the wet season.This leads to the conclusionthat the present Cuiab• data are not influ- 0 ' I • I ' I ' I ' enced by the Pantanal area. 300 320 340 360 380 400 MIXING RATIO { pprnv ) Summary Figure 10. Average carbon dioxide mixing ratio and stan- This work describesresults of a field campaignorganized by dard deviationsof the mean, all profiles of 1992. INPE, using a Brazilian made Bandeirante aircraft, showing the first observations of carbon dioxide, nitrous oxide, and methane obtainedby the INPE group in the biomassburning Carbon Dioxide region of central Brazil. Profilesof ozone and carbon monox- Mixing ratio averagesfor carbondioxide, seen in Figure 10, ide were also obtained.The aircraft expeditionwas organized showa rather uniform profile, indicatinga well-mixedtropo- in April and Septemberof 1992 in Brazil in cooperationwith spherebelow 4 km, with an overall averageclose to 353 ppmv. the major NASA TRACE A mission.General characteristics However, considerablelower and larger mixing ratios have of the biomassburning behavior of the Brazilian cerrado in been observed,and will be describedelsewhere. The horizontal 1992 are shown. The INPE aircraft crew was instructed to bars are the standard deviations from the means at the differ- avoidthe direct samplingof sourceareas, so that the observed ent heights. profiles should reflect reasonablywell-mixed air, not burning plumes. Methane Vertical profilesduring the wet and dry seasonsare shownat Resultsfor methane are shownin Figure 11. The left panel sites of the remote savanna regions in central Brazil. The showsresults for Cuiabfi,and the right panel showsresults for smallestvariability between wet and dry seasonsis observedin

4.0 • , , , I , , , , 4.0

3.5-

3.0-

I- 2.0-

I- 1.5- i' -r 1.5 1.0- 1.0

WET I•¾ 0.5 0.5

0.0 ...... 0.0 1650 1;• 1• 1• 18• 1650 1700 1750 1800 METHANE MIXING RATIO (ppbv) Figure 11. Methane mixingratios for Cuiabfi and Porto Nacional, for dry and wet seasonperiods of 1992. 23,980 KIRCHHOFFAND ALVAL•: AIRCRAFTEXPEDITION IN BRAZIL the nitrous oxide data, which in terms of mixing ratios, vary Troposphericchemical composition measurements in Brazil during between 310 and 320 ppbv. The carbon dioxidemixing ratios the dry season,J. Atmos. Chem.,2, 233-256, 1985. averagearound 353 ppmv, and showan almostconstant mixing Delany, A. C., P. Haagenson,S. Walters, A. F. Wartburg, and P. J. Crutzen, Photochemicallyproduced ozone in the emissionfrom ratio with height, but showspatial variability probablyassoci- large-scaletropical vegetation fires, J. Geophys.Res., 90, 2425-2429, ated to local sources. 1985. For ozone and carbon monoxide the results confirm earlier Fishman,J., C. E. Watson,J. C. Larsen, and J. A. Logan, Distribution sondeand ground-baseddata that showconsistent mixing ratio of TroposphericOzone Determinedfrom SatelliteData, J. Geophys. increasesbetween wet and dry seasonperiods. Ozone may Res., 95, 3599-3617, 1990. Fishman,J., K. Fakhruzzman,B. Cros, and D. Nganga,Identification increasefrom 15 ppbv in the wet period to 80 ppbv in a dry of widespreadpollution in the SouthernHemisphere deduced from seasonobservation. The factor of increaseis even larger for satelliteanalyses, Science, 252, 1693-1696, 1991. CO, which shows, consistently,concentrations in the small Fishman, J., J. M. Hoell Jr., R. D. Bendura, V. W. J. H. Kirchhoff, and range of 80 to 100 ppbv in the wet period, and valuesup to 600 R. J. McNeal, The NASA GTE TRACE A experiment(September- ppbv in the dry seasonobservation period. The verticalprofiles October, 1992),J. Geophys.Res., this issue. Fuelberg,H. E., R. O. Loring Jr., M. V. Watson, M. C. Sinha, K. E. made at Cuiabfi and Porto Nacional indicate consistently Pickering,A.M. Thompson,and D. P. McNamara, Trace A trajec- larger concentrationsof methane in the dry season.Cuiabfi tory intercomparison,2, Isentropicand kinematicmethods, J. Geo- showsbetween 15 and 40 ppbv larger concentrationsin the dry phys.Res., this issue. seasonthan Porto Nacional, which may be the result of smol- Goldammer, J., Tropical wild-land fires and global changes:Prehis- dering fires north of the Cuiabfi station. toric evidence,present regimes,and future trends, in Global Bio- massBurning: Atmospheric, Climatic, and BiosphericImplications, edited by J. S. Levine, pp. 83-91, MIT, Cambridge,Mass., 1991. Gregory,G. L., E. V. Browell,and L. S. Gahan,Boundary layer ozone: Acknowledgments. The authors are grateful to local support at An airborne surveyabove the Amazon Basin,J. Geophys.Res., 93, INPE Cuiabfi, especiallyto Jos6Roberto Chagas,and to Ermelinda 1452-1468, 1988. deLamonicaFreire of the University of Mato Grosso.At Porto Na- Griffith, D. W. T., W. G. Mankin, M. T. Coffey,D. E. Ward, and A. cional,support was offered by the localstate university, UNITINS. The Riebau,FTIR remotesensing of biomassburning emissions of CO2, technicalteam at Natal headedby Jos6Ribeiro Alvesincludes Adauto CO, CH4, CH20, NO, NO2, NH3, and N20, in Global Biomass Motta, Francisco Raimundo da Silva, and Carlos Roberto da Silva. At Burning:Atmospheric, Climatic, and BiosphericImplications, edited S•o Jos6dos Camposthe techniciansheaded by Marcelo Arafijo are by J. S. Levine, pp. 230-239, MIT, Cambridge,Mass., 1991. Luiz Mangueira, Vitor Portezani, and Angelica de Jesus. Special Hoell, J. M., et al., Operational overviewof the NASA GTE/CITE 3 thanks are due to the aircraft crew Pedro Celso Santos and Luiz airborne instrumentintercomparisons for sulfur dioxide,hydrogen Monteiro. The authors are grateful to Maria A. O. da Silva for her sulfide, carbonylsulfide, dimethyl sulfide, and carbon disulfide,J. collaborationwith the methane measurements,to Randy Cofer and Geophys.Res., 98, 23,291-23,304, 1993. Glen Sachseof NASA LangleyResearch Center for calibrationgases Jacob,D. J., and S.C. Wofsy, Photochemistryof biogenicemissions that were generouslyprovided, to the TRACE A missionteam, espe- over the Amazon forest,J. Geophys.Res., 93, 1477-1486, 1988. cially R. J. McNeal of NASA Headquarters,and to J. M. Hoell of Jacob,D. J., and S.C. Wofsy, Budgetsof reactivenitrogen, hydrocar- NASA LangleyResearch Center for their encouragementand support, bons, and ozone over the Amazon Forest during the wet season,J. and to CNPq and FAPESP for financialsupport. 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Oliveira, M. A. S., V. W. J. H. Kirchhoff, and P. C. Alvalfi, Perfor- biomassburning as a sourceof carbonmonoxide and ozone in the mance of a monitor for atmosphericmethane measurements,Rev. southernhemisphere tropics: A satellite analysis,J. Geophys.Res., Bras.Geofis., 11(1), 57-64, 1993. 95, 16,443-16,450, 1990. Pickering,K. E., et al., Convectivetransport of biomassburning emis- sionsover Brazil during TRACE A, J. Geophys.Res., this issue. P. C. Alvala and V. W. J. H. Kirchhoff, INPE, Av. dos Astronautas Thompson,A.M., et al., Where did troposphericozone over southern 1758,Caixa Postal515, 12201S5o Jos6 doe Campos,S5o Paulo, Brazil. Africa and the tropical Atlantic come from in October 19927 In- sightsfrom TOMS, GTE/TRACE A, and SAFARI 92, J. Geophys. Res., this issue. (ReceivedMarch 21, 1995;revised July 21, 1995; Watson, C. E., J. Fishman,and H. G. Reichle Jr., The significanceof acceptedSeptember 13, 1995.)