title: Airborne measurements of isoprene and monoterpene emissions from southeastern U.S. forests.
abstract: Isoprene and monoterpene emission rates are essential inputs for atmospheric chemistry models that simulate atmospheric oxidant and particle distributions. Process studies of the biochemical and physiological mechanisms controlling these emissions are advancing our understanding and the accuracy of model predictions but efforts to quantify regional emissions have been limited by a lack of constraints on regional distributions of ecosystem emission capacities. We used an airborne wavelet-based eddy covariance measurement technique to characterize isoprene and monoterpene fluxes with high spatial resolution during the 2013 SAS (Southeast Atmosphere Study) in the southeastern United States. The fluxes measured by direct eddy covariance were comparable to emissions independently estimated using an indirect inverse modeling approach. Isoprene emission factors based on the aircraft wavelet flux estimates for high isoprene chemotypes (e.g., oaks) were similar to the MEGAN2.1 biogenic emission model estimates for landscapes dominated by oaks. Aircraft flux measurement estimates for landscapes with fewer isoprene emitting trees (e.g., pine plantations), were about a factor of two lower than MEGAN2.1 model estimates. The tendency for high isoprene emitters in these landscapes to occur in the shaded understory, where light dependent isoprene emissions are diminished, may explain the lower than expected emissions. This result demonstrates the importance of accurately representing the vertical profile of isoprene emitting biomass in biogenic emission models. Airborne measurement-based emission factors for high monoterpene chemotypes agreed with MEGAN2.1 in landscapes dominated by pine (high monoterpene chemotype) trees but were more than a factor of three higher than model estimates for landscapes dominated by oak (relatively low monoterpene emitting) trees. This results suggests that unaccounted processes, such as floral emissions or light dependent monoterpene emissions, or vegetation other than high monoterpene emitting trees may be an important source of monoterpene emissions in those landscapes and should be identified and included in biogenic emission models.
authors.affiliation: Dept. of Civil, Environmental & Construction Engineering, University of Central Florida, Orlando, FL, USA; Pacific Northwest National Laboratory, Richland, WA 99354, USA.
authors.forename: Haofei
authors.initials: H
authors.lastname: Yu
authors.affiliation: Pacific Northwest National Laboratory, Richland, WA 99354, USA; Department of Earth System Science, 3200 Croul Hall, University of California, Irvine, CA 92697-3100, USA. Electronic address: alex.guenther@uci.edu.
authors.forename: Alex
authors.initials: A
authors.lastname: Guenther
authors.affiliation: Pacific Northwest National Laboratory, Richland, WA 99354, USA; Department of Earth System Science, 3200 Croul Hall, University of California, Irvine, CA 92697-3100, USA.
authors.forename: Dasa
authors.initials: D
authors.lastname: Gu
authors.affiliation: Chemical Sciences Division, Earth System Research Laboratory, NOAA, Boulder, CO, USA; CIRES, University of Colorado, Boulder, CO, USA.
authors.forename: Carsten
authors.initials: C
authors.lastname: Warneke
authors.affiliation: National Risk Management Research Laboratory, U.S. Environment Protection Agency, Raleigh, NC, USA.
authors.forename: Chris
authors.initials: C
authors.lastname: Geron
authors.affiliation: Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA, USA.
authors.forename: Allen
authors.initials: A
authors.lastname: Goldstein
authors.affiliation: Institute of Atmospheric and Cryospheric Sciences, University of Innsbruck, Innsbruck, Austria.
authors.forename: Martin
authors.initials: M
authors.lastname: Graus
authors.affiliation: Institute of Atmospheric and Cryospheric Sciences, University of Innsbruck, Innsbruck, Austria.
authors.forename: Thomas
authors.initials: T
authors.lastname: Karl
authors.affiliation: National Center for Atmospheric Research, Boulder, CO, USA.
authors.forename: Lisa
authors.initials: L
authors.lastname: Kaser
authors.affiliation: Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA, USA.
authors.forename: Pawel
authors.initials: P
authors.lastname: Misztal
authors.affiliation: Chemical Sciences Division, Earth System Research Laboratory, NOAA, Boulder, CO, USA; CIRES, University of Colorado, Boulder, CO, USA.
authors.forename: Bin
authors.initials: B
authors.lastname: Yuan
keywords: Aircraft flux measurements; Biogenic volatile organic compounds; Isoprene; Model of Emissions of Gases and Aerosols from Nature (MEGAN); Monoterpenes