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 AND R. L. SNELL 6 The Amazon BoundaryLayer Experiment (ABLE 2A) used data from aircraft, ground-based, and satellite platforms to characterize the chemistry and dynamics of the lower atmosphere over the Amazon Basinduring the early-to-middle dry season, July and August 1985. This paper reportsthe conceptual framework and experimental approach used in ABLE 2A and serves as an introduction to the detailed papers whichfollow in this issue. The results of ABLE 2A demonstrate that isoprene, methane, carbon dioxide,nitric oxide,dimethylsulfide, and organicaerosol emissions from soilsand vegetation play a major role in determining the chemicalcomposition of the atmospheric mixed layer over undisturbed forest and wetland environments. As the dry season progresses, emissions from 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 experimentfocused on assessing the role of biosphere-atmosphere interactions on the chemistry of the troposphere over relatively pristine tropical forests and wet- lands. The early phase of the Amazonian dry season was se- lected 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 tropo- spheric chemistry over the Amazon in April-May 1987. This series of missions is stimulated by the need to better under- stand the role of the tropics in global atmospheric chemistry [National Academy of Sciences (N,4S), 1984] and, more specifi- cally, to investigate processes which might lead to the en- hanced 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 Na- cional 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 x Atmospheric Sciences Division, NASA Langley Research Center, Hampton, Virginia. 2 HarvardUniversity, Cambridge, Massachusetts. 3 Univ•½rsity of Virginia, Charlottesville, Virginia. '• InstitutoNacional de Pesquisas Espaciais, SaoJose dosCampos, Brazil. 5 Earth Science and Applications Division, National Aeronautics and SpaceAdministration, Washington, D.C. 6 NASA Wallops FlightCenter, Wallops Island, Virginia. Copyright 1988 by the AmericanGeophysical Union. Paper number 7D0700. 0148-0227/88/007D-0700505.00 NASA Tropospheric Chemistry Program. This paper reports the overall experimental designfor ABLE 2A, the general wea- ther 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 hypoth- eses that (1) tropical rain forest environments are characterizedby relatively intense sources of 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 gases and aerosolsto high altitudes where they impact global tropospheric chemistry; and (3) the tropical troposphere is a region of intense photochemical ac- tivity where oxidation of certain biogenic trace gases (e.g., isoprene (C5H8)) produces sourcesof gaseous products (e.g., CO) that may be significant to global budgets. A very limited number of measurements on emissions of gases from 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 prelimi- nary N•O data to global sourceestimates indicated that tropi- cal 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 sources of CH 4 and CO in the Amazon might also be significant to global budgets [Wofsy et al., 1986]. Results from ABLE 2A substantiate these previous studies and provide considerable additional evidence for im- portant sourcesof biogenic carbon, nitrogen, and sulfur gases in the Amazon ecosystem. Previous studies have also shown that biomass burning, related primarily to agricultural practices, is an important source of CO, ozone (03), and nonmethane hydrocarbons (NMHC) to the atmosphere over the savannahs and rain for- ests of Brazil during the dry season [Crutzen et al., 1985; Delany et al., 1985; Greenberg et al., 1984]. Results from ABLE 2A also demonstrate an increasing influenceof biomass 1351