Isoprene Fluxes from an Oak-Dominated Temperate Forest
Isoprene is a biogenic volatile organic compound. Its oxidation in the atmosphere affects both the production of tropospheric ozone and secondary aerosol formation. Isoprene production by plants, therefore, has implications for the control of regional air quality and global climate change. Scientists at Oak Ridge National Laboratory recently conducted a study to understand these isoprene emissions and to test predictive models at multiple scales. The study took place at the Missouri Ozark AmeriFlux (MOFLUX) site in central Missouri, an oak-hickory dominated forest. Ecosystem fluxes of isoprene emissions were measured during the 2011 growing season. The isoprene flux measurements were used to test understanding of the controls on isoprene emission from hourly to seasonal timescales with a state-of-the-art emission model, MEGAN (Model of Emissions of Gases and Aerosols from Nature). Isoprene emission rates observed during the drought of 2011 reached 53.3 mg m-2 h-1 (217 nmol m-2 s-1), the highest ever recorded for any ecosystem in the world. The MEGAN model correctly predicted isoprene emission rates before drought, but its performance deteriorated as the drought progressed (in response to water stress). Overall, MEGAN’s performance was robust and could explain 90% of the observed variance in the measured fluxes, but the response of isoprene emission to drought stress is a major source of uncertainty. Since isoprene is chemically reactive in the atmosphere, it is critically important to understand these emissions as well as to incorporate this process into atmosphere-biosphere models.
Potosnak, M. J., L. LeStourgeon, S. G. Pallardy, K. P. Hosman, L. H. Gu, T. Karl, C. Gerone, and A. B. Guenther. 2014. “Observed and Modeled Ecosystem Isoprene Fluxes from an Oak-Dominated Temperate Forest and the Influence of Drought Stress,” Atmospheric Environment 84, 314–22. DOI:10.1016/j.atmosenv.2013.11.055.