Biogenic Sources of Oxygenated Hydrocarbons in the Troposphere

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The impacts of volatile organic compounds (VOCs emitted by vegetation on atmospheric chemistry are under increasing scrutiny, especially since they play a central role in photochemical smog formation. Past investigations have focused on hydrocarbon components of VOC's, but recently large quantities of oxygenated hydrocarbons (OHC's), such as methanol and acetone, have been found in the air of rural forests, leading to questions about their origins and roles in tropospheric chemistry. Preliminary measurements indicate that methanol can be emitted by leaves at high rates, similar to that for isoprene emission, and that conifer buds emit substantial quantities of acetone, suggesting that vegetation is a significant source of volatile OHC's. The proposal addresses several key questions. 1) How much methanol and acetone are emitted by various species of plants? 2) What different plant parts (e.g., buds, leaves, bark, etc.) emit methanol and acetone? 3) How do environment, phenology, season, and plant stress influence methanol and acetone emissions? The effects of environment and stresses will be examined in controlled laboratory experiments. Fluxes of OHC's from different plant families will be assessed as part of the Rural Oxidants in a Southern Environment (ROSE II) study in a southeastern forest (summer 1992), and from field surveys in the boulder area. Fluxes will be measured using bud, leaf, branch, and stem enclosures with OHC analysis by gas chromatography. This work will provide the first comprehensive overview of plant methanol and acetone emissions, which will be useful in atmospheric modeling of tropospheric chemistry, particularly of rural areas, and will provide estimation of natural sources of atmospheric methanol before methanol-containing fuels come on line.