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EVALUATION OF FOREST CANOPY MODELS FOR ESTIMATING ISOPRENE EMISSIONS
Citation:
Lamb, B., T Pierce*, D. D. Baldocchi, E. Allwine, S. Dilts, H. Westberg, C D. Geron*, A. Guenther, L. Klinger, P. Harley, AND P. Zimmerman. EVALUATION OF FOREST CANOPY MODELS FOR ESTIMATING ISOPRENE EMISSIONS. JOURNAL OF GEOPHYSICAL RESEARCH 101(D17):22787-22797, (1996).
Impact/Purpose:
Published Journal Article
Description:
During the summer of 1992, isoprene emissions were measured in a mixed deciduous forest near Oak Ridge, Tennessee. Measurements were aimed at the experimental scale-up of emissions from the leaf level to the forest canopy to the mixed layer. Results from the scale-up study are compared to different canopy models for determining the leaf microclimate as input to isoprene emission algorithms. These include (1) no canopy effects, (2) a simple vertical scaling canopy model with a leaf energy balance, and (3) a numerical canopy model which accounts for leaf-sun geometries, photosynthesis, respiration, transpiration, and gas transport in the canopy. Initial evaluation of the models was based upon a standard emission rate factor of 90 μgC g−1 hr−1 (0.42 nmol g−1 s−1) taken from leaf cuvette measurements and a biomass density factor of 203 g m−2 taken from biomass surveys and a flux footprint analysis. The results indicated that predicted fluxes were consistent among the models to within approximately ±20%, but that the models overestimated the mean flux by about a factor of 2 and overestimated the maximum observed flux by 30 to 50%. Adjusting the standard emission factor and biomass density each downward by 20% yielded predicted means approximately 20% greater than the observed means and predicted maxima approximately 25% less than the observed maxima. Accounting for changes in biomass density as a function of direction upwind of the tower improved the overall model performance.
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Journal URL
Evaluation of Forest Canopy Models for Estimating Isoprene Emissions (PDF, NA pp, 3092 KB, about PDF)