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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 109, D02309, doi:10.1029/2002JD003353, 2004

Characterization and dry deposition of carbonaceous aerosols in a wet tropical forest canopy

H. W. Loescher

School of Forest Resources and Conservation, University of Florida, Gainesville, Florida, USA

J. A. Bentz

Particulate Systems Research Center and Nuclear Science and Engineering Institute, University of Missouri, Columbia, Columbia, Missouri, USA

S. F. Oberbauer

Biological Sciences, Florida International University, Miami, Florida, USA

T. K. Ghosh

Particulate Systems Research Center and Nuclear Science and Engineering Institute, University of Missouri, Columbia, Columbia, Missouri, USA

R. V. Tompson

Particulate Systems Research Center and Nuclear Science and Engineering Institute, University of Missouri, Columbia, Columbia, Missouri, USA

S. K. Loyalka

Particulate Systems Research Center and Nuclear Science and Engineering Institute, University of Missouri, Columbia, Columbia, Missouri, USA

Abstract

Carbon aerosol concentration was measured using an impactor on a 42 m tower over a wet tropical forest in northeast Costa Rica. Samples were collected at three different heights, 42, 21, and 2 m, for 2 months during the wet season in 1998. Winds originated from two directions, southeast from the Caribbean Sea and west from the continental isthmus. Concentrations were normalized by the fraction of dry sampling time during the collection. The distribution was negatively skewed for the range of aerodynamic diameter aerosols measured. The main size constituent was in the class 4.7–3.3 μm, accounting for ∼0.70 μg C mol⁻¹. No significant difference was found in the distribution of aerosol carbon with height, suggesting a well-mixed column of air, minimal resuspension, and that the source was from surrounding land use types. Functional relationships were developed to describe the loading of aerosols to the atmosphere and the removal by precipitation. Deposition was estimated using these relationships, combined with three different estimates of velocity deposition derived from (1) aerodynamic and canopy conductance, (2) aerodynamic and momentum conductance, and (3) traditional estimates of gravitational settling diffusion, impaction, and interception. Annual deposition estimates were 2.9, 5.0, and 9.6 kg ha⁻¹ yr⁻¹, respectively. Concentrations of carbon aerosols reported here are as much as two orders of magnitude higher than those reported elsewhere. Annual dry deposition estimates, however, were within the range of other estimates but were likely underestimated. Potential effects on deposition caused by seasonal burns and El Niño–Southern Oscillation are discussed.

Received 23 December 2002; accepted 3 November 2003; published 27 January 2004.

Index Terms: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 4801 Oceanography: Biological and Chemical: Aerosols (0305); 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions; 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 1610 Global Change: Atmosphere (0315, 0325).

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Citation: Loescher, H. W., J. A. Bentz, S. F. Oberbauer, T. K. Ghosh, R. V. Tompson, and S. K. Loyalka (2004), Characterization and dry deposition of carbonaceous aerosols in a wet tropical forest canopy, J. Geophys. Res., 109, D02309, doi:10.1029/2002JD003353.

Copyright 2004 by the American Geophysical Union.