title: An ecosystem-scale perspective of the net land methanol flux: synthesis of micrometeorological flux measurements.
abstract: Methanol is the second most abundant volatile organic compound in the troposphere and plays a significant role in atmospheric chemistry. While there is consensus about the dominant role of living plants as the major source and the reaction with OH as the major sink of methanol, global methanol budgets diverge considerably in terms of source/sink estimates reflecting uncertainties in the approaches used to model, and the empirical data used to separately constrain these terms. Here we compiled micrometeorological methanol flux data from eight different study sites and reviewed the corresponding literature in order to provide a first cross-site synthesis of the terrestrial ecosystem-scale methanol exchange and present an independent data-driven view of the land-atmosphere methanol exchange. Our study shows that the controls of plant growth on the production, and thus the methanol emission magnitude, and stomatal conductance on the hourly methanol emission variability, established at the leaf level, hold across sites at the ecosystem-level. Unequivocal evidence for bi-directional methanol exchange at the ecosystem scale is presented. Deposition, which at some sites even exceeds methanol emissions, represents an emerging feature of ecosystem-scale measurements and is likely related to environmental factors favouring the formation of surface wetness. Methanol may adsorb to or dissolve in this surface water and eventually be chemically or biologically removed from it. Management activities in agriculture and forestry are shown to increase local methanol emission by orders of magnitude; they are however neglected at present in global budgets. While contemporary net land methanol budgets are overall consistent with the grand mean of the micrometeorological methanol flux measurements, we caution that the present approach of simulating methanol emission and deposition separately is prone to opposing systematic errors and does not allow taking full advantage of the rich information content of micrometeorological flux measurements.
authors.affiliation: Institute of Ecology, University of Innsbruck, Innsbruck, Austria ; European Academy of Bolzano, Bolzano, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Wohlfahrt
authors.affiliation: Belgian Institute for Space Aeronomy, Brussels, Belgium.
authors.forename: C
authors.initials: C
authors.lastname: Amelynck
authors.affiliation: Research Station Agroscope, Climate and Air Pollution Group, Zürich, Switzerland.
authors.forename: C
authors.initials: C
authors.lastname: Ammann
authors.affiliation: Karlsruhe Institute of Technology, IMK-IFU, Garmisch-Partenkirchen, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Arneth
authors.affiliation: Karlsruhe Institute of Technology, IMK-IFU, Garmisch-Partenkirchen, Germany ; Institute of Agricultural Sciences, ETH Zürich, Zürich, Switzerland.
authors.forename: I
authors.initials: I
authors.lastname: Bamberger
authors.affiliation: Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA, USA.
authors.forename: A H
authors.initials: AH
authors.lastname: Goldstein
authors.affiliation: Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA.
authors.forename: L
authors.initials: L
authors.lastname: Gu
authors.affiliation: Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, Richland, WA, USA.
authors.forename: A
authors.initials: A
authors.lastname: Guenther
authors.affiliation: Institute of Ion Physics and Applied Physics, University of Innsbruck, Innsbruck, Austria.
authors.forename: A
authors.initials: A
authors.lastname: Hansel
authors.affiliation: Exchanges Ecosystems-Atmosphere, Department Biosystem Engineering (BIOSE), University of Liege, Gembloux, Belgium.
authors.forename: B
authors.initials: B
authors.lastname: Heinesch
authors.affiliation: Department of Physical Geography and Ecosystem Science, Lund University, Lund, Sweden.
authors.forename: T
authors.initials: T
authors.lastname: Holst
authors.affiliation: Institute of Agricultural Sciences, ETH Zürich, Zürich, Switzerland.
authors.forename: L
authors.initials: L
authors.lastname: Hörtnagl
authors.affiliation: Institute of Meteorology and Geophysics, University of Innsbruck, Innsbruck, Austria.
authors.forename: T
authors.initials: T
authors.lastname: Karl
authors.affiliation: Royal Meteorological Institute, Brussels, Belgium.
authors.forename: Q
authors.initials: Q
authors.lastname: Laffineur
authors.affiliation: Research Station Agroscope, Climate and Air Pollution Group, Zürich, Switzerland.
authors.forename: A
authors.initials: A
authors.lastname: Neftel
authors.affiliation: School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA.
authors.forename: K
authors.initials: K
authors.lastname: McKinney
authors.affiliation: School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA.
authors.forename: J W
authors.initials: JW
authors.lastname: Munger
authors.affiliation: Department of Forestry, University of Missouri, Columbia, MO, USA.
authors.forename: S G
authors.initials: SG
authors.lastname: Pallardy
authors.affiliation: Department of Atmospheric Sciences, Texas A&M University, College Station, TX, USA.
authors.forename: G W
authors.initials: GW
authors.lastname: Schade
authors.affiliation: Department of Earth System Science, University of California, Irvine CA 92697, USA.
authors.forename: R
authors.initials: R
authors.lastname: Seco
authors.affiliation: Belgian Institute for Space Aeronomy, Brussels, Belgium.
authors.forename: N
authors.initials: N
authors.lastname: Schoon