Exchange of Volatile Organic Compounds (VOC) From Different VOC Categories Between Tropical Tree Species and the Atmosphere at a Remote Forest Site in the Amazon Basin.
Abstract
As part of the Large Scale Biosphere Atmosphere Experiment over Amazonia (LBA-EUSTACH), we examined the diel patterns of VOC exchange in the wet season 1999 at a remote field site in Rondonia, Brazil. Vertical gradients of ambient air mixing ratios in and above the primary rainforest clearly indicated emission of isoprene by the forest. For monoterpenes a similar flux could hardly be resolved, caused by atmospheric mixing ratios of an order of magnitude lower than for isoprene. Direct measurements with a branch enclosure system identified isoprene as well as a monoterpene emitters. The diel emission patterns of both types reacted identically towards the fluctuating light and temperature, indicating that close metabolic pathways with a strong light dependence were involved in the actual emission. Contrasting the isoprenoids, oxygenated compounds such as short-chain organic acids and aldehydes were nearly exclusively deposited. Direct exchange measurements on the branch level mainly exhibited uptake of formic and acetic acid and corresponding aldehydes for all plant species in both seasons, although diel, seasonal and interspecies variations were observed. Even though other physiological and physicochemical parameters may contribute, the uptake of organic acids and aldehydes was found to be primarily a function of the ambient atmospheric mixing ratios. The linear dependence suggests a bi-directional exchange behavior. Vertical profile measurements in and above the primary forest canopy further strengthened the assumption that the forest is rather a sink than a source of these oxygenated compounds, originating from photochemical oxidation of reactive precursor compounds rather than direct emission from vegetation.
- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2002
- Bibcode:
- 2002AGUSM.A51E..06K
- Keywords:
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- 0315 Biosphere/atmosphere interactions;
- 0365 Troposphere: composition and chemistry;
- 0368 Troposphere: constituent transport and chemistry