HR: 11:20h
AN: A21F-05    [PDF]
TI: Field Observations of Increased Isoprene Emissions Under Ozone Fumigation: Implications for Tropospheric Chemistry?
AU: * Sparks, J P
EM: jps66@cornell.edu
AF: Cornell University, Dept. of Ecology and Evolutionary Biolgy, Ithaca, NY 14853 United States
AU: Greenberg, J P
EM: greenber@ucar.edu
AF: National Center for Atmospheric Research, Atmospheric Chemistry Division, Boulder, CO 80307 United States
AU: Harley, P C
EM: harley@ucar.edu
AF: National Center for Atmospheric Research, Atmospheric Chemistry Division, Boulder, CO 80307 United States
AU: Guenther, A B
EM: guenther@ucar.edu
AF: National Center for Atmospheric Research, Atmospheric Chemistry Division, Boulder, CO 80307 United States
AB: Isoprene is the most abundant biogenic hydrocarbon released from vegetation and plays a key role in the chemistry of the lower atmosphere. Isoprene is produced and emitted by many plant species, yet the reason plants produce this seemingly wasteful carbon compound is still in debate in the plant physiology community. It has been proposed that isoprene may protect plant leaves from thermal damage or damage from oxidant exposure by stabilizing cellular and chloroplast membranes or by direct reactions between exogenous isoprene and oxidative species. As part of the Chemical Emission, Loss, Transformation and Interactions within Canopies (CELTIC) study held at Duke Forest during the summer of 2003, we used dynamic cuvette systems to fumigate leaves of sweet gum ({\it Liquidambar styraciflua}) with ozone at partial pressures ranging from 0 to 300 ppbv. During fumigations, the effluent air was monitored using infrared gas analysis, on-line proton-transfer-reaction mass spectrometry (PTR-MS) and gas chromatography to quantify changes in partial pressure of CO$_{2}$, water vapor, isoprene and other volatile organics. At fumigations above 100 ppbv ozone, leaf-isoprene emission increased 20-35% compared to pre-fumigation. To our knowledge, this is the first reported observation of increased isoprene emission under ozone fumigation. Over the timescale of our measurements (several hours), isoprene emissions, once elevated, did not decrease even after fumigation levels were reduced. The increase in isoprene emission could potentially be due to upregulation of the isoprene synthase gene or simply an increase in the production (or reallocation) of subcellular isoprene precursor species. However, our measurements did not elucidate or eliminate a particular mechanism. If increases in isoprene emission in response to ozone are common among isoprene emitting species, the feedback implications for the atmosphere could be large. Both a mechanistic understanding of the upregulation process and knowledge of the distribution of the response across plant species are needed for future model parameterization.
DE: 0315 Biosphere/atmosphere interactions
DE: 0322 Constituent sources and sinks
DE: 0330 Geochemical cycles
DE: 0345 Pollution--urban and regional (0305)
DE: 0365 Troposphere--composition and chemistry
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting