The Amazon Boundary Layer Experiment ABLE ... - Wiley Online Library

JOURNAL OF GEOPHYSICAL

RESEARCH, VOL. 93, NO. D2, PAGES 1351-1360, FEBRUARY 20, 1988

The Amazon Boundary Layer Experiment (ABLE 2A)' Dry Season 1985 R. C. HARRISS, 1 S.C. WOFSY, 2 M. GARSTANG, 3 E. V. BROWELL, 1 L. C. B. MOLION, '• R. J. MCNEAL, 5 J. M. HOELL,JR.,1 R. J. BENDURA, 1 S. M. BECK, • R. L. NAVARRO, 6 J. T. RILEY, 6 ANDR. L. SNELL 6 The Amazon Boundary Layer Experiment(ABLE 2A) used data from aircraft, ground-based,and satelliteplatformsto characterizethe chemistryand dynamicsof the lower atmosphereover the Amazon Basinduring the early-to-middledry season,July and August 1985. This paper reports the conceptual framework and experimental approach used in ABLE 2A and servesas an introduction to the detailed paperswhich follow in this issue.The resultsof ABLE 2A demonstratethat isoprene,methane,carbon dioxide,nitric oxide,dimethylsulfide, and organicaerosolemissionsfrom soilsand vegetationplay a major role in determiningthe chemicalcompositionof the atmosphericmixed layer over undisturbed forest and wetland environments.As the dry seasonprogresses,emissionsfrom both local and distant biomass burning become an important source of carbon monoxide, nitric oxide and ozone in the atmosphere over the central Amazon Basin.

INTRODUCTION

The Amazon Boundary Layer Experiment (ABLE 2A) was conducted in the Amazon region of Brazil during July and August 1985. This experimentfocusedon assessingthe role of biosphere-atmosphereinteractions on the chemistry of the

troposphere over relativelypristinetropicalforestsand wetlands. The early phase of the Amazonian dry season was selected as the experiment period for ABLE 2A in order to provide the best opportunities for characterizing the chemistry of the undisturbed (nonprecipitating) atmospheric boundary layer over tropical forests and wetlands. The next mission in the ABLE program (ABLE 2B) will focus on the influence of disturbed meteorological conditions (wet season) on tropospheric chemistry over the Amazon in April-May 1987. This series of missions is stimulated by the need to better understand the role of the tropics in global atmospheric chemistry [National Academy of Sciences(N,4S), 1984] and, more specifically, to investigate processes which might lead to the enhanced concentrations of carbon monoxide (CO) in the remote tropical upper troposphere which were observed by the NASA Measurement of Air Pollution from Space (MAPS) experiment during the November 1981 STS-2/OSTA-1 space shuttle mission [Reichle et al., 1986]. The design and execution of ABLE 2A was a collaboration of U.S. and Brazilian scientists sponsored by the National Aeronautics and Space Administration (NASA) and Instituto Nacional de Pesquisas Espaciais (INPE). Important facilities and logistical support were also provided by the Instituto Nacional de Pesquisas da Amazonia (INPA), Manaus, Brazil. These experiments are part of a longer-term study of the chemistry of the atmospheric boundary layer supported by the Global Tropospheric Experiment (GTE) component of the

NASA Tropospheric Chemistry Program. This paper reports the overall experimental designfor ABLE 2A, the general weather conditions which prevailed during the experiment period, and a very brief overview of the results.A seriesof following papers report detailed results of individual studies. SCIENTIFIC

RATIONALE

Both theoretical studiesand available data support hypotheses that (1) tropical rain forest environments are

characterizedby relatively intense sourcesof certain biogenic gases and aerosols; (2) the world's largest rain forest in the Amazon Basin is a region of frequent atmospheric instability with intense convective activity, resulting in the potential for rapid mixing of biogenic gasesand aerosolsto high altitudes where they impact global tropospheric chemistry; and (3) the tropical troposphere is a region of intense photochemical activity where oxidation of certain biogenic trace gases (e.g., isoprene (C5H8)) produces sourcesof gaseousproducts (e.g., CO) that may be significant to global budgets. A very limited number of measurements on emissions of

gasesfrom soils have been conducted in tropical ecosystems (see Seiler and Conrad [1987] for a review). Closed chamber techniques have been used to measure fluxes of nitrous oxide

(N20), carbon dioxide (CO2), and methane (CH4) in both natural and disturbed areas of tropical forest [e.g., Conrad and

Seller, 1982; Seller et al., 1984]; extrapolation of some preliminary N•O data to global sourceestimatesindicated that tropical forest soils might contribute as much as 50% of the annual flux of N20 to the atmosphere [Keller et al., 1983; Keller et al., 1986]. Ambient air samples collected at several ground sitesin Amazonia and adjacent areas added further support to the concept of a major source of N20 from forest soils and indicatedthat natural sourcesof CH 4 and CO in the Amazon might also be significant to global budgets [Wofsy et al., x AtmosphericSciences Division,NASA LangleyResearchCenter, 1986]. Results from ABLE 2A substantiate these previous Hampton, Virginia. studies and provide considerable additional evidence for im2 Harvard University,Cambridge,Massachusetts. portant sourcesof biogenic carbon, nitrogen, and sulfur gases 3 Univ•½rsity of Virginia,Charlottesville, Virginia. '• InstitutoNacionalde Pesquisas Espaciais, Sao JosedosCampos, in the Amazon ecosystem. Brazil. Previous studies have also shown that biomass burning, 5 Earth Scienceand ApplicationsDivision, National Aeronautics related primarily to agricultural practices, is an important and SpaceAdministration, Washington, D.C. source of CO, ozone (03), and nonmethane hydrocarbons 6 NASA WallopsFlight Center,WallopsIsland,Virginia. (NMHC) to the atmosphere over the savannahs and rain forCopyright 1988 by the AmericanGeophysicalUnion. ests of Brazil during the dry season [Crutzen et al., 1985; Delany et al., 1985; Greenberg et al., 1984]. Results from Paper number 7D0700. 0148-0227/88/007D-0700505.00 ABLE 2A also demonstrate an increasinginfluence of biomass 1351

1352

HARRISS ETAL..'ABLE 2A

GTE/ABLE 2A

burning on trace gas and aerosol concentrationsin the boundary layer as the experiment progressedinto dry-seasoncon-

In situ measurements of CO 2, CO, CH 4, NMHC, NO (nitric oxide), N20, 03, DMS (dimethylsulfide),aerosolcom-

ditions.

position, and meteorological parameters were conducted during most research flights. Figure 3 shows a layout of the

A variety of photochemical and chemical mass balance models have been published which predict globally significant

sourcesof CO 2, CO, CH 4, and N20 in tropical regions[e.g., Hameed and Stewart, 1979; Khalil and Rasmussen, 1981; Logan et al., 1981; Crutzen and Gidel, 1983; Pinto et al., 1983].

The magnitudeof natural sourcesof NO,,, NMHC, CO, and CH 4 and the rates of transport of thesegasesfrom the boundary layer to the free troposphere are major sourcesof uncertainty in current global photochemical and mass balance model

calculations.

instrumentation

aboard

the Electra.

In addition

to extensive

in situ data for straight and level flight legs at selected altitudes over specificlandscapes,a total of 66 vertical soundings from 150 m to approximately 3500 m were conducted. The approximate locations of these vertical soundings are illustrated by the black dots on Figure 2d. The typical approach in each ABLE 2A flight involved a high-altitude pass over a research area using the downlooking UV Differential Absorption Lidar (DIAL) to deter-

mine the two dimensional distribution of aerosols, ozone, and clouds between the aircraft and surface along the entire flight various chemical species[Lawson and Winchester, 1979; Orsini track. Using the real-time lidar data, subsequent flight altiet al., 1982], and in determining the composition of precipi- tudes were selectedto sample in and above the atmospheric tation. During the dry season, aerosol concentrations in some boundary layer, in haze layers, and in other features of interest tropical regions are dominated by biomassburning emissions indicated by the remotely sensedaerosol and/or ozone distri[Cachier et al., 1985]. The ABLE 2A aerosol measurement butions. During flight legs in the boundary layer, the UV program focused on determining the size distribution and DIAL was used in an up-looking mode to measure aerosol, composition of both boundary layer and free troposphereaer- ozone, and cloud distributions above the aircraft.

Aerosolsproduced in tropical ecosystemsmay play important roles as cloud condensationnuclei, in chemicalbudgetsof

osols.

Ground-BasedExperiments APPROACH

The scientific objectivesof ABLE 2A were accomplished through a coordinatedprogram of measurementsby U.S. and Brazilian scientistsfrom the NASA Lockheed Electra aircraft, a tethered balloon, a 45-m meteorologicaltower, surfacetrace gas and meteorologicalsites, and free-flyingsondes.The experimentswere conductedduring July and August 1985 in the Brazilian portion of the Amazon Basin. A complementary program of studies, termed the Amazon Ground Emissions

(AGE) Program, operatedthree surfacesitesduring the same time period, including the researchvesselR/V Amanai sampling along the Rio Solomoies and Rio Amazonas, an an-

chored floating laboratory in Lago Calado (80 km west of Manaus, Brazil), and a forest site in Reserva Ducke near

Manaus. A list of ABLE 2A and AGE principal investigators and measurementparametersis presentedin Table 1. Aircraft Experiments

The centerpieceof ABLE 2A was a seriesof 15 flightswith the fully instrumentedNASA Electra aircraft.The flightswere divided into four types of experiments: (1) Studies of atmosphericboundary layer chemistryand dynamicsduring fairweather conditions: (2) studies of the influence of active convection on the chemistry and vertical distribution of selected gas and aerosolspeciesin the lower and midtroposphere;(3) studiesof the influence of large, open water areas of the Rio Negro River and associatedfloodplains on local boundary layer dynamicsand chemicalprocesses;and (4) long-distance flights acrossthe Amazon Basin to obtain a near-synoptic descriptionof troposphericchemistryover the entire central Amazon ecosystem.These flights, together with the more continuous surface, tethered balloon, and sonde measurements at

Reserva Ducke near Manaus, provided the most comprehensive picture to date of atmosphericchemistryover equatorial tropical rain forests,rivers, and floodplains.Figure 1 shows the geographicalregionsincludedfor eachexperimentalobjective in the ABLE 2A. Figures 2a-2d show the general flight profiles for each type of experiment listed in Table 2, which summarizesthe dates,times, and classificationof each flight.

At Reserva Ducke, an INPA biological reserve 20 km northeast of Manaus, Brazil, studies focused on boundary

layer dynamics and source/sinkrelationshipsfor N20, NO, CO2, CH,•, NMHC, 03, and aerosols.The data from these studies provide particularly important insights into chemical processesin the nocturnal boundary layer which could not be sampled with aircraft. The tethered balloon system made 432 soundingsof the atmosphere, up to 1 km above the surface. Meteorological data were also obtained from 174 free-flying sondes, and 03 profiles were obtained from 27 ozonesonde releases.

The floating laboratory in Lago Calado and R/V Amanai served as platforms for CH,• flux studies in wetland and river environments. Samples of sediment gas were also collected for isotopic analysis. METEOROLOGICAL

CONDITIONS

The week preceding the start of aircraft operations from Manaus (July 11-17) was characterized by frequent, widespread disturbed weather over the Amazon Basin. Precipitating convectivecloud clustersoccurred both during day and night hours, resulting in 1-22 mm of rain in the Manaus area per day. This rainy period was produced by a high-latitude system penetrating the middle and upper troposphere, resulting in widespread convective storms north of the equator. These conditions, typical of what is expected in the late wet season,produced high soil moisture and inhibited almost all biomassburning. Beginning July 17-18, the region from Manaus to Belem and south of the Solimoes and Amazon rivers came progressively under the domination of a subtropical anticyclone which gradually migrated north, becoming centered over northeast Brazil. The first ABLE 2A flight in Brazil, on July 18, encountered residual instability in the form of scattered showers.ABLE 2A flights on July 19 and 21 were ideal for studying the chemistry of the undisturbed boundary layer. By July 19 the anticyclone was well established over northeast Brazil; radiosonde data showed a decrease in atmospheric precipitable water from 4.7 cm on July 18 to 3.1 cm on July 21. The large-scale atmospheric conditions which were domi-

GTE/ABLE 2A

HARRISS ETAL.:ABLE 2A

1353

TABLE 1. Principal Investigatorsin the ABLE 2A and AGE Field Expedition July-August 1985

Investigator

Institution

Meinrat Sherwin

O. Andreae M. Beck

Florida State University NASA Langley ResearchCenter

Edward

V. Browell

NASA Langley Research Center

aerosols, ozone profiles

State University of New York at Albany University of Virginia NASA Langley Research Center NASA Langley ResearchCenter Simpson Weather Associates

meteorological studies

United

Investigation

States

sulfur measurements

airborne meteorological data

David R. Fitzjarrald Michael Garstang Gerald L. Gregory Robert C. Harriss Charles L. Martin Pamela A. Matson John M. Melack

NASA

A. Rasmussen

Center

University of California at Santa

Reinhold

Ames Research

Steven C. Wofsy Patrick

National

Glen W. Sachse Daniel I. Sebacher Robert W. Talbot Arnold L. Torres Peter

Vitousek

ozone

methane

meteorological studies nitrous

oxide

limnology

Barbara

Oregon Graduate Center University of Washington NASA Langley Research Center NASA Langley Research Center NASA Langley Research Center NASA GSFC Wallops Flight Facility Stanford University Harvard University

Jeffrey E. Richey

meteorological studies

isoprene/other trace gases methane, carbon dioxide carbon monoxide methane aerosols nitric oxide

nitrous

oxide

nitric oxide, carbon dioxide

R. Zimmerman

Center

For

hydrocarbons

Atmospheric Research Brazil

Elen

Cutrim

Pedro

L. S. Dias

Volker Luiz

W. J. H. Kirchhoff C. B. Molion

P. Artaxo Carlos

I. M.

Netto

A. Nobre

Moreira-Nordemann

Halley S. Pinheiro Alberto

Setzer

Federal University of Para University of S•o Paulo

meteorological studies meteorological studies

INPE

ozone

INPE

meteorological studies

University of S•o Paulo

aerosols

INPE

meteorological studies precipitation chemistry

INPE

Federal University of Para University of S•o Paulo

nant during ABLE 2A are illustrated by a GOES satellite image for July 21, 1501 hours UT (Plate 1, top). An atmospheric structure typical for a midmorning fair-weather, undisturbed boundary layer is illustrated by the remotely sensed aerosol and ozone distribution (e.g.,from the UV DIAL lidar) shown in Plate 1 (color panels). The relative atmospheric backscattering illustrated in the top color panel of Plate 1

radiation

measurements

satellite imagery

On August 2 an equatorial vortex with an associatedeasterly wave, extending from the mouth of the Amazon to 12øN, advanced rapidly westward [Garstang et al., this issue]. These changes in the large scale dynamics produced an increased frequency of mesoscaleconvective cloud activity and precipitation during August 2 and 3. These conditions were selected for exploratory studies on the influence of disturbed weather reflects the vertical distribution of aerosol as a function of conditions on the chemistry of the planetary boundary layer. altitude. During fair weather the aerosol is highly stratified; in The influence of convective activity on aerosol and ozone is Plate 1 the mixed layer of the atmosphereis indicated by the illustrated in Plate 2. While it is important to note that safety relatively high backscatteringfrom the surface to 1.0 km, and considerations and aircraft performance limits restricted studthe trade wind inversion is indicated by the further decreasein ies to peripheral areas of individual precipitating clouds, the backscattering at 3.3 km. The bottom color panel in Plate 1 contrast with undisturbed conditions (Plate 1, bottom panels) illustrates a general stratification in ozone, with con- is obvious. This two-dimensional lidar depiction of atmocentrations of 5-15 parts per billion by volume (ppbv) in the spheric structure, as reflected in aerosol and ozone distrimixed layer, increasing to 25-30 ppbv above the trade wind bution over approximately 175 km of tropical forest, illusinversion. As solar energy input to the forest canopy increases trates the complexity of a planetary boundary layer influenced from sunrise to midday, the mixed layer of the atmosphere by active tropical convective clouds, which penetrate through grows in height to typically 1.5 km on a fair-weather day the trade wind inversion to altitudes above 4 km. The lidar [Martin et al., this issue]. Sequential vertical soundings and data (Plate 2) show an area with a suppressedmixed layer; straight and level flight elements(see Figure 2a) during 5- to small cumulus clouds with bases at 750 m were observed, in 6-hour missions provided an assessmentof coupled meteoro- contrast to a mixed layer height of approximately 1500 m logical and chemical processes.These flights were often timed expected for 1830 hours. A downdraft of relatively clean (i.e., to coincidewith the period of maximum mixed layer growth. low aerosol) air is penetrating to the surface behind an active The predominantly undisturbed weather conditions dis- convective cluster. The details of meteorological conditions during specific cussed previously were present until August 1-2, when an upper tropospheric cold-air mass penetrated the study area. flights and their influence on the distribution of tropospheric

1354

HARRISSœx^I•.: ABLE 2A

GTE/ABLE

ANAUS

ELEM

T

0

3oo

600

(to

I 00

I GA

15

(RELA'i'tVE UNITS)

3..O 20*'

1.0

5.5 S

RE

TI

R

KSCATTER;N

59 o

Plate 1. (Top) GOES satelliteimageillustratingthe fair-weatherconditionsover the southernportion of the Amazon Basin encounteredduring most of July-August 1985' (bottom) airborne lidar remotely sensedvertical distribution of relativeatmosphericbackscatteringand ozoneduring typical fair-weathercondition.

2A

GTE/ABLE2A

HARRISS ETAL.:ABLE2A

1355

A]•LE-2A FLT #13 0-3-EI5 D]::STUR:•ED - DAY (#2) AERDSDL

&e

e

PROF!LES

< ]:R)

84'

843

t04

t849

t852

4.e

1.e

l

mm

2.5 ..

..

.ml,

.

l.e

mm

m•

Ol•L

13;•011E PROFILE:•

CPP:!)U)

Plate 2. Airbornelidar remotelysensedverticaldistributionof (top) relativeatmospheric backscattering and (bottom) ozone in the vicinity of disturbedweather.

1356

HAP, RISS ETAL.'ABLE2A

GTE/ABLE2A

3151DV4

GTE/ABLE 2A

H^RmSS ETAL..'ABLE 2A

1357

(d) -C'ROSS-BAStN Fig. 2. Simplified illustration of aircraft flight profiles used for (a) undisturbed (fair) weather boundary layer sampling, (b) disturbed weather (precipitating) boundary layer sampling, (c) studies of the boundary layer over land-river interfaces, and (d) cross-basinchemical surveys(dots indicate locations of vertical profiles).

gasesand aerosolsare found in the individual papers in this

issue.Overall, the ABLE 2A missionwas conductedduring the early and middle phasesof the 1985 dry season;the total precipitation measured at Manaus in July (103 mm) and August (60 mm) were, based on long-term records, well within the range expected for dry-seasonconditions. OVERVIEW

OF RESULTS

etation as sourcesof NO and CsH 8 to the atmosphericmixed layer and, consequently, the potential for photochemical pro-

duction of 0 3 during the oxidation of CsH s is a particularly important discovery [see Kaplan et al., this issue; Torres and Buchan, this issue; Zimmerman et al., this issue; Jacob and

Wofsy,this issue;[Rasmussenand Khalil, this issue].Theoretihave demonstrated

that concentrations

0 3 over undisturbed regions.The soil source of NO measured

by Kaplan et al. [this issue] frequentlyenhancedmixed layer concentrationsto 25-60 pptv [Torres and Buchan,this issue],

indicatingthepotentialfor photochemical productionof 0 3 in

In this brief overview of results, we highlight only those ABLE 2A findings which we believe to be important to new conceptual advances in understanding large-scale atmospheric chemical processesin the tropics. This approach to providing an executive summary is not meant to lessen the importance of the ABLE 2A data sets on biomass burning emissions [Andreae et al., this issue], CO distribution [Sachse et al., this issue], and 0 3 distribution [Gregory et al., this issue; Browell et al., this issue], which add considerably to the preliminary data obtained by Crutzen et al. [1985]. The important role of Amazonian forest soils and veg-

cal considerations

required to initiate 0 3 production during the photochemical oxidation of CsH s. There was no information on NO concentrations over remote tropical rain forests prior to ABLE 2A to assessthe potential for tropical troposphericsourcesof

of

NO greater than 10-15 parts per trillion by volume (pptv) are

the mixed layer over undisturbedAmazon rain forests[Jacob and Wofsy, this issue].

The relativelyhigh concentrations of biogenicC•H s in the mixed layer over rain forests [Zimmerman et al., this issue; Rasmussenand Khalil, this issue] are also hypothesizedto be the dominant control on mixed layer concentrations of OH [Jacob and Wofsy, this issue; Rasmussen and Khalil, this issue]. These results lead to the interesting conclusion that natural emissions from the tropical biosphere influence the photochemicalenvironment of the overlying atmosphere,lifetimes of reduced gasesin the tropical atmosphere,and consequently, the role of tropical ecosystemsin global trace gas

budgets.Processes related to the productionof NO x in tropical soils and the photochemicaloxidation of CsH s in the tropical atmosphererequire further intensivestudy. The vertical distribution of gas phase formic and acetic acid that was measured in the forest canopy and their diurnal behavior suggest that these organic acids are also derived from photochemical reactions associatedwith C•H 8 oxidation and,

1358

HARRISS ETAL..'ABLE 2A

GTE/ABLE

2A

TABLE 2. Summaryof the Flights ConductedDuring the ABLE 2A Expedition

Departure Mission

Number

Arrival

Flight Date

July 11

July 12

Time, UT

1503

1423

Location

Time, UT

NASA Wallops Island VA (WAL)*

1958

Puerto Rico (MJSJ)

2001

Location Puerto

Rico

International Airport, San Juan (MJSJ)* Eduardo

Gomes

Airport Manaus, Brazil, (SBEG)*

10

Purpose latitudinal survey/ transit flight

latitudinal survey/ transit flight

July 18

1306

Manaus

1839

Manaus

July 19

1206

Manaus

1802

Manaus

July 21

1058

Manaus

1659

Manaus

July 23

1154

Manaus

1759

Val De Caes Airport, Belem, Brazil (SBBE)*

west-east survey

July 24 July 25

1200 2357

Belem Manaus

1825 0544

Manaus

survey

Manaus

July 26

2218

Manaus

0418

Manaus

undisturbed boundary layer (night) undisturbed boundary layer (night)

July 29

1552

Manaus

2146

Manaus

undisturbed boundary layer (day) undisturbedboundary layer (day) undisturbed boundary layer (day)

forest-river

interface

(day) 11 12

13 14-1

July 31

Aug. 2 Aug. 3 Aug. 5

0659

Manaus

1323

1440

Manaus

2051

1350 1121

Manaus Manaus

1949 1628

Manaus

forest-fiver

Manaus

(night-day) disturbed boundary layer disturbed boundary layer

Manaus

Tabatinga Airport, Tabatinga, Brazil (SBTT)*

interface

east-west survey

(Tefe to Tabatinga)

Aug. 5 Aug. 6

1812

Tabatinga

2128

Manaus

survey

15

1150

Manaus

1801

Manaus

east-west survey

16 17 18

Aug. 8 Aug. 9 Aug. 12

1150

Manaus

1757

Belem

west-east survey

1235

Belem

1828

Manaus

survey

1308

Manaus

1824

Roosevelt Roads, NS,

19

Aug. 13

1430

Puerto

1827

Puerto Rico (MJNR)* Langley AFB, Hampton, Va. (LAFB)*

latitudinal survey/ transit flight latitudinal survey/ transit flight

14-2

(Manaus to TeFe)

Rico

International Airport, San Juan (MJSJ)* *Airport location identifier (a three- or four-characterICAO-assigned code).

possibly, by direct emission from the forest canopy [Andreae et al., this issue]. In precipitation, these organic acids account for about one-half of the total anion equivalents, producing acid rain of natural origin. Biogenic emissionsfrom soils and vegetation are the dominant source of sulfur to the mixed layer over Amazonia [Andreae and Andreae, this issue]; however, the measured sources of reduced sulfur from the upland forest environment were considerably lower than had been predicted by extrapolation of North American data. Dimethylsulfide is a primary sulfur species in the mixed layer, ranging in concentration from about 40 ppt at ground level to 1 ppt at 5 km. The total sulfur

flux from the tropicalforestis estimatedto be 3-8 nmol m-2 min-•, which is similar per unit area to the flux from the

acidic aerosol found over industrialized regions [Talbot et al., this issue].

Sequentialprofilesof CO2 taken in time and spaceover the entire Amazon Basin demonstrated the utility of an aircraft platform for large-scale studies of carbon exchange between the biosphere and the atmosphere [Wofsy et al., this issue]. Forest photosynthetic and respiratory processesinfluencedthe

COe distribution through the entire column of the atmospheric mixed layer. Selectedsampling of COe variations in specific areas of forest or wetland can provide large-scale carbon fix-

ation rate data at scalesof 10'•-105km•. This capabilitycan be utilized in future ABLE studies to resolve questions concerning the role of tropical regions as sourcesand/or sinks for

CO2.

ocean surface. However, since the ocean is 70% of the Earth's

In summary, the ABLE 2A documented, for dry-seasonconsurface, its contribution to the global sulfur budget exceeds ditions, the very important role of biosphere-atmosphereinterthe forest contribution. actions in determining atmospheric chemical processesin the Aerosols over Amazonia were composed primarily of mixed layer over undisturbed rain forests. In addition, the organic carbon (> 80% of the aerosol mass),suggestinga bio- burning of biomass, in both the savannahsand forested regenic origin. ABLE 2A data showed a remarkable spatial ho- gions of northern Brazil, was shown to influenceair chemistry mogeneity in aerosol composition across the entire Amazon over the entire region. However, during these dry months, Basin. Because of the high levels of ammonium ion, the convective activity is at a minimum, and consequently,couAmazon aerosol was acid-base neutral, in contrast to the

pling betweenthe Amazon biosphereand global troposphere

GTE/ABLE

HARRISS ET AL.' ABLE

2A

I [

1359

2A

J

r

II

o =.

lø I

1360

HARRISS ETAL.:ABLE 2A

is at a minimum. The ABLE 2B wet seasonstudy (April-May, 1987) will be a first attempt at understanding the potential role of tropical ecosystems in global tropospheric chemistry during a time of year when convective activity couples the biosphere to the entire overlying tropospheric column on an almost daily basis. Acknowledgments. The ABLE 2A project acknowledgesthe excellent support and cooperation of the following individuals: Joan McLaughlin and Susan Fruchter, NASA Headquarters; Larry Kohler, American Consulate, Sao Paulo, Brazil; Helen Thompson, Howard Curfman, and Dennis Owen, the Bionetics Corporation; Adauto Motta and Carlos Nobre, Instituto Nacional de Pequisas Espaciais; Elen Cutrim, University of Para, Brazil; and Hubert Schubart, Instituto Nacional de Pesquisas da Amazonia. This paper is dedicated to John P. Mugler, Jr., who had the wisdom and patience to guide us successfullythrough the initial stages of the GTE and ABLE.

REFERENCES

Andreae, M. O., and T. W. Andreae, The cycle of biogenic sulfur compounds over the Amazon Basin, 1, Dry season,J. Geophys. Res., this issue.

Andreae, M. O., et al., Biomass-burning emissions and associated haze layers over Amazonia, J. Geophys.Res., this issue. Browell, E. V., G. L. Gregory, R. C. Harriss, and V. W. J. H. Kirch-

hoff, Troposphericozone and aerosoldistributions ;acrossthe Amazon Basin, J. Geophys.Res., this issue. Cachier, H., P. Buat-Menard, and M. Fortagne, Source terms and source strengths of the carbonaceous aerosol in the tropics, J. Atmos. Chem., 3, 469-489, 1985.

Conrad, R., and W. Seiler, Arid soils as a source of atmospheric carbon monoxide, Geophys.Res. Lett., 9, 1353-1356, 1982. Crutzen, P. J., and L. T. Gidel, A two-dimensional photochemical model of the atmosphere, 2, The troposphere budgets of the an-

thropogenicchlorocarbons,CO, CH,•, CH3Cl and the effect of various NO x sourceson troposphericozone, J. Geophys.Res., 88, 6641-6661,

1983.

Crutzen, P. J., A. C. Delany, J. Greenberg, P. Haagenson, L. Heidt, R. Lueb, W. Pollock, W. Seiler, A. Wartburg, and P. Zimmerman, Tropospheric chemical composition measurementsin Brazil during the dry season,J. Atmos. Chem.,2, 233-256, 1985. Delany, A. C., P. Haagensen, S. Walters, A. F. Wartburg, and P. Crutzen, Photochemically produced ozone in the emission from large-scaletropical vegetation fires, J. Geophys.Res., 90, 2425-2429, 1985.

Garstang, M., et al., Trace gas exchangesand convectivetransports over the Amazonian rain forest, J. Geophys.Res., this issue. Greenberg, J. P., P. Zimmerman, L. Heidt, and W. Pollock, Hydrocarbon and carbon monoxide emissions from biomass burning in Brazil, J. Geophys.Res., 89, 1350-1354, 1984.

Gregory, G. L., E. V. Browell, and L. S. Warren, Boundarylayer ozone: An airborne survey above the Amazon Basin, J. Geophys. Res., this issue.

Hameed, S., and R. W. Stewart, Latitudinal distribution of the sources of carbon monoxide in the troposphere, Geophys. Res. Lett., 6, 841-844, 1979.

Jacob, D. J., and S.C. Wofsy, Photochemistry of biogenic emissions over the Amazon forest, J. Geophys.Res., this issue. Kaplan, W. A., S.C. Wofsy, M. Keller, and J. M. da Costa, Emission

GTE/ABLE 2A

Khalil, M. A. K., and R. A. Rasmussen, Atmospheric trace gases:

Possibility of sourcesin the southern hemisphere, Atmos. Environ., 15, 1331-1334, 1981.

Lawson, D. R., and J. W. Winchester, Sulfur, potassium, and phosphorus associationsin aerosolsfrom South American tropical rain forests,J. Geophys.Res., 84, 3723-3727, 1979. Logan, J. A., M. J. Prather, S.C. Wofsy, and M. B. McElroy, Troposphericchemistry: A global perspective,J. Geophys.Res., 86, 72107254, 1981.

Martin, C., D. Fitzjarrald, M. Garstang, A. P. Oliveira, S. Greco, and E. Browell, Structure and growth of the mixing layer over the Amazonian rain forest, J. Geophys.Res., this issue. National Academy of Sciences, Global Tropospheric Chemistry: A Plan for Action, 194 pp., National Academy Press, Washington, D.C.,

1984.

Orsini, C. Q., P. Artaxo, and M. H. Tabacniks, Preliminary data on atmospheric aerosol of the Amazon Basin, Atmos. Environ., 16, 2177-2181, 1982.

Pinto, J.P., Y. L. Yung, D. Rind, G. L. Russell,J. A. Lerner, J. E. Hansen, and S. Hameed, A general circulation model study of atmosphericcarbon monoxide, J. Geophys.Res.,88, 3691-3702, 1983. Rasmussen,R. A., and M. A. K. Khalil, Isoprene over the Amazon Basin, J. Geophys.Res., this issue. Reichle, H. G., V. S. Connors, J. A. Holland, W. D. Hypes, H. A. Wallio, J. C. Casas, B. B. Gormsen, M. S. Saylor, and W. D. Hesketh, Middle and upper tropospheric carbon monoxide mixing ratios as measured by a satellite-borne remote sensor during November 1981, J. Geophys.Res.,91, 10,865-10,887, 1986. Sachse, G. W., R. C. Harriss, J. Fishman, G. F. Hill, and D. R. Cahoon, Carbon monoxide over the Amazon Basin during the 1985 dry season,J. Geophys.Res.,this issue. Seiler, W., and R. Conrad, Contribution of tropical ecosystemsto the

global budgetsof trace gases,especiallyCH4, H e, CO, and NeO, The Geophysiologyof Amazonia, edited by R. E. Dickinson, pp. 133-160, John Wiley, New York, 1987. Seiler, W., R. Conrad, and D. Scharffe, Field studiesof methane emission from termite nests into the atmosphere and measurementsof methane uptake by tropical soils,J. Atmos.Chem.,1, 171-186, 1984. Talbot, R. W., M. O. Andreae, T. W. Andreae, and R. C. Harriss, Regional aerosol chemistryof the Amazon Basin during the dry season,J. Geophys.Res.,this issue. Torres, A. L., and H. Buchan, Tropospheric nitric oxide measurements over the Amazon Basin, J. Geophys.Res.,this issue. Wofsy, S.C., W. A. Kaplan, M. Keller, and R. A. Rasmussen,Seasonal and synopticmeasurementsof trace gasesin the Amazon Basin, 1983-1984: External influences on atmospheric composition, Eos Trans. AGU, 67, 247, 1986.

Wofsy, S.C., R. C. Harriss, and W. A. Kaplan, Carbon dioxide in the atmosphereover the Amazon Basin,J. Geophys.Res.,this issue. Zimmerman, P. R., J.P. Greenberg, and C. Westberg, Measurements of atmospherichydrocarbonsand biogenicemissionof fluxesin the Amazon boundary layer, J. Geophys.Res.,this issue. S. M. Beck, R. J. Bendura, E. V. Browell, R. C. Harriss, and J. M.

Hoell, Jr., Atmospheric SciencesDivision, NASA Langley Research Center, Hampton, VA 23665. M. Garstang, University of Virginia, Charlottesville,VA 22903. R. J. McNeal, Earth Science and Applications Division, National Aeronauticsand SpaceAdministration,Washington,DC 20546. L. C. B. Molion, Instituto Nacional de Pesquisas Espaciais,

C. P. 515, 12.200 Sao Jose dos Campos, SP, Brazil. R. L. Navarro, J. T. Riley, and R. L. Snell, NASA Wallops Flight of NO and depositionof 0 3 in a tropical forestsystem,J. Geophys. Center, Wallops Island, VA 23337. Res., this issue. S.C. Wofsy, Harvard University, Cambridge, MA 02138. Keller, M., T. J. Goreau, S.C. Wofsy, W. A. Kaplan, and M. B. McElroy, Production of nitrous oxide and consumption of methane by forest soils,Geophys.Res. Lett., 10, 1156-1159, 1983. (Received March 12, 1987; Keller, M., W. A. Kaplan, and S.C. Wofsy, Emissionsof NeO, CH 4, and CO from tropical forest soils, J. Geophys. Res., 91, 11,791revised August 11, 1987; 11,803, 1986. acceptedAugust 24, 1987.)