HR: 0800h
AN: A51B-0046    [Abstracts]
TI: Deducing a Canopy Reduction Factor for Biogenic Emission Modeling
AU: * Karl, T
EM: tomkarl@ucar.edu
AF: NCAR, 1850 Table Mesa Dr, Boulder, CO 80305 United States
AU: Guenther, A
EM: guenther@ucar.edu
AF: NCAR, 1850 Table Mesa Dr, Boulder, CO 80305 United States
AB: The IPCC 2001 report states that "there is a serious discrepancy between the isoprene emissions derived by [Guenther et al., 1995] based on a global scaling of emission" . and "highlights a key uncertainty in global modeling of highly reactive trace gases: namely, what fraction of primary emissions escapes immediate reaction/removal in the vegetation canopy or immediate boundary layer and participates in the chemistry on the scales represented by global models?". A recent modeling study [Makar et al., 1999] suggested that up to 40 % of isoprene can be lost due to in-canopy chemistry. However, up to date only limited experimental datasets have been used to constrain canopy reduction factors (CRF) . Based on our recent CELTIC (Chemistry, Emission, Loss and Transformation in Canopies) initiative we measured VOC emissions above tropical, deciduous and evergreen ecosystems. In this paper we infer a new parameterization for modeling a CRF due to chemically short-lived biogenic compounds of the form: CRF = h/(a x u* x tau +h) (h: canopy height [m], u*: friction velocity [m/s], tau: lifetime [s], a: dimensionless fitting parameter a=1.5 +/- 0.1). This parameterization is based on results obtained during recent field studies in combination with a random walk model. For isoprene we find that the CRF is on the order of 2-5 % for typical daytime conditions. Loss rates for isoprene are somewhat smaller but within the range of previously reported values [Strong et al., 2004], [Stroud et al., 2005]. Many reactive terpenoid compounds (such as beta-caryophellene) with lifetimes on the order of minutes can be substantially reduced (e.g. up to 60-80 %) before they escape the forest canopy. References: Guenther, A., C.N. Hewitt, D. Erickson, and R. Fall, A global model of natural volatile organic compound emissions, Journal of geophysical research, 100 (D/5), 8873-8892, 1995. Makar, P., J. Fuentes, D. Wang, R. Staebler, and H. Wiebe, Chemical processing of biogenic hydrocarbons within and above a temperate deciduous forest, J. geophys. res., 104 (D3), 3581-3603, 1999. Strong, C., J.D. Fuentes, and D. Baldocchi, Reactive hydrocarbon flux footprints during canopy senescence, Agricultural and Forest Meteorology, 127 (3-4), 159-173, 2004. Stroud, C., P.A. Makar, T. Karl, A. Guenther, C. Geron, A.A. Turnipseed, E. Nemitz, B. Baker, M. Potosnak, J.D. Fuentes, H. McCarthy, and R. Oren, Role of Canopy-Scale Photochemistry in Modifying Biogenic-Atmosphere Exchange of Reactive Terpene Species: Results from the CELTIC Field Study, Journal of Geophysical Research-Atmospheres, in press, 2005.
DE: 0315 Biosphere/atmosphere interactions (0426, 1610)
DE: 0368 Troposphere: constituent transport and chemistry
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005