HR: 1330h
AN: A32A-0109    [PDF]
TI: Relationships Among Canopy Scale Energy Fluxes and Isoprene Flux Using Eddy Covariance Measurements Over Multiple Growing Seasons
AU: * Pressley, S N
EM: spressle@wsunix.wsu.edu
AF: Washington State University, Department of Civil and Environmental Engineering, Pullman, WA 99164-2910 United States
AU: Lamb, B K
EM: blamb@wsu.edu
AF: Washington State University, Department of Civil and Environmental Engineering, Pullman, WA 99164-2910 United States
AU: Westberg, H
EM: westberg@mail.wsu.edu
AF: Washington State University, Department of Civil and Environmental Engineering, Pullman, WA 99164-2910 United States
AB: Isoprene is one of the most abundant biogenic trace gases in the troposphere. Biogenic trace gases affect tropospheric chemistry by forming gaseous and particulate secondary products in conjunction with anthropogenic emissions that contribute to the degradation of air quality. Our understanding of the impact isoprene has on tropospheric photochemistry is hampered by our limited knowledge of the biosphere-atmosphere exchange process, and thus the inability to accurately quantify the biogenic emission inventory. Isoprene emissions are regulated by many environmental variables; the most important variables are known to be temperature and light. The research summarized here seeks to improve our understanding of biogenic emissions from forest ecosystems as a basis for advancing our ability to describe the role of biogenics in regional and global atmospheric chemical cycles. Biogenic emission models, such as BEIS (Biogenic Emission Inventory System) rely on above canopy environmental parameters and below canopy scaling factors to estimate canopy scale biogenic hydrocarbon fluxes. This type of model can predict biogenic emissions well, however, the required input is extensive, and for regional applications, it can be cumbersome. Based on the assumption that isoprene emission rates are enzymatic (a function of temperature, light, and historical temperature), we propose that sensible heat flux can be a surrogate for above canopy temperature and light when estimating isoprene fluxes at the canopy scale. In addition, sensible heat flux may be a better indicator of the canopy interaction with incoming energy, as opposed to scaling above canopy parameters. Thus, the use of surface energy fluxes such as sensible heat flux is an attempt to combine the biological (enzymatic) and meteorological processes that affect the biosphere-atmosphere exchange of isoprene. Since surface energy budgets are an integral part of mesoscale meteorological models, this could potentially be a useful tool for including biogenic emissions into regional atmospheric models. Long-term measurements of isoprene flux have been collected above a northern hardwood forest at the AmeriFlux site located at the University of Michigan Biological Station (UMBS) as part of the Program for Research on Oxidants: Photochemistry, Emissions, and Transport (PROPHET). Measurements have been made every summer since 1998 using eddy covariance techniques, and the data are now available for determining the relationship between isoprene flux and surface energy fluxes. Using this long-term dataset we hope to improve our understanding of isoprene emissions and, thus, improve our ability to include isoprene emissions in regional and global atmospheric chemistry models.
DE: 0315 Biosphere/atmosphere interactions
DE: 0345 Pollution--urban and regional (0305)
DE: 0365 Troposphere--composition and chemistry
DE: 0368 Troposphere--constituent transport and chemistry
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting