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Published December 18, 2003 | Published
Journal Article Open

Organic compounds present in the natural Amazonian aerosol: Characterization by gas chromatography–mass spectrometry


As part of the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA)-Cooperative LBA Airborne Regional Experiment (CLAIRE) 2001 campaign in July 2001, separate day and nighttime aerosol samples were collected at a ground-based site in Amazonia, Brazil, in order to examine the composition and temporal variability of the natural "background" aerosol. We used a high-volume sampler to separate the aerosol into fine (aerodynamic diameter, AD < 2.5 μm) and coarse (AD > 2.5 μm) size fractions and quantified a range of organic compounds in methanolic extracts of the samples by a gas chromatographic-mass spectrometric technique. The carbon fraction of the compounds could account for an average of 7% of the organic carbon (OC) in both the fine and coarse aerosol fractions. We observed the highest concentrations of sugars, sugar alcohols, and fatty acids in the coarse aerosol samples, which suggests that these compounds are associated with primary biological aerosol particles (PBAP) observed in the forest atmosphere. Of these, trehalose, mannitol, arabitol, and the fatty acids were found to be more prevalent at night, coinciding with a nocturnal increase in PBAP in the 2–10 μm size range (predominantly yeasts and other small fungal spores). In contrast, glucose, fructose, and sucrose showed persistently higher daytime concentrations, coinciding with a daytime increase in large fungal spores, fern spores, pollen grains, and, to a lesser extent, plant fragments (generally >20 μm in diameter), probably driven by lowered relative humidity and enhanced wind speeds/convective activity during the day. For the fine aerosol samples a series of dicarboxylic and hydroxyacids were detected with persistently higher daytime concentrations, suggesting that photochemical production of a secondary organic aerosol from biogenic volatile organic compounds may have made a significant contribution to the fine aerosol. Anhydrosugars (levoglucosan, mannosan, galactosan), which are specific tracers for biomass burning, were detected only at low levels in the fine aerosol samples. On the basis of the levoglucosan-to-OC emission ratio measured for biomass burning aerosol, we estimate that an average of ∼16% of the OC in the fine aerosol was due to biomass burning during CLAIRE 2001, indicating that the major fraction was associated with biogenic particles.

Additional Information

Copyright 2003 by the American Geophysical Union. Received 19 July 2003; revised 16 September 2003; accepted 30 September 2003; published 18 December 2003. This study was carried out as part of the Large-Scale Atmosphere-Biosphere Experiment in Amazonia (LBA). It was made possible by fundamental support through the Max Planck Society. P. Artaxo acknowledges financial support from "Fundação de Amparo à Pesquisa do Estado de São Paulo", W. Maenhaut is indebted to the Belgian Federal Office for Scientific, Technical and Cultural Affairs, and the "Fonds voor Wetenschappelijk Onderzoek–Vlaanderen" for research support, and P. Taylor, R. Flagan and M. Glovsky acknowledge support from the Philip Morris External Research Program. We sincerely thank the staff of Manaus Energia who supported us in the course of the measurements through the supply and maintenance of infrastructure.

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August 19, 2023
October 18, 2023