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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 15, issue 17 | Copyright
Biogeosciences, 15, 5395-5413, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 06 Sep 2018

Research article | 06 Sep 2018

Synthetic ozone deposition and stomatal uptake at flux tower sites

Jason A. Ducker1, Christopher D. Holmes1, Trevor F. Keenan2,3, Silvano Fares4, Allen H. Goldstein3, Ivan Mammarella5, J. William Munger6, and Jordan Schnell7 Jason A. Ducker et al.
  • 1Department of Earth, Ocean, and Atmospheric Science, Florida State University, Tallahassee, Florida, USA
  • 2Lawrence Berkeley National Laboratory, University of California, Berkeley, California, USA
  • 3Department of Environmental Science, Policy, and Management, University of California, Berkeley, California, USA
  • 4Council of Agricultural Research and Economics (CREA), Research Centre for Forestry and Wood, Arezzo, Italy
  • 5Institute for Atmosphere and Earth System Research/Physics, P.O. Box 68, Faculty of Science, University of Helsinki, Finland
  • 6Department of Earth and Planetary Sciences, Northwestern University, Evanston, Illinois, USA
  • 7NOAA Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey, USA

Abstract. We develop and evaluate a method to estimate O3 deposition and stomatal O3 uptake across networks of eddy covariance flux tower sites where O3 concentrations and O3 fluxes have not been measured. The method combines standard micrometeorological flux measurements, which constrain O3 deposition velocity and stomatal conductance, with a gridded dataset of observed surface O3 concentrations. Measurement errors are propagated through all calculations to quantify O3 flux uncertainties. We evaluate the method at three sites with O3 flux measurements: Harvard Forest, Blodgett Forest, and Hyytiälä Forest. The method reproduces 83% or more of the variability in daily stomatal uptake at these sites with modest mean bias (21% or less). At least 95% of daily average values agree with measurements within a factor of 2 and, according to the error analysis, the residual differences from measured O3 fluxes are consistent with the uncertainty in the underlying measurements.

The product, called synthetic O3 flux or SynFlux, includes 43 FLUXNET sites in the United States and 60 sites in Europe, totaling 926 site years of data. This dataset, which is now public, dramatically expands the number and types of sites where O3 fluxes can be used for ecosystem impact studies and evaluation of air quality and climate models. Across these sites, the mean stomatal conductance and O3 deposition velocity is 0.03–1.0cms−1. The stomatal O3 flux during the growing season (typically April–September) is 0.5–11.0nmol O3m−2s−1 with a mean of 4.5nmol O3m−2s−1 and the largest fluxes generally occur where stomatal conductance is high, rather than where O3 concentrations are high. The conductance differences across sites can be explained by atmospheric humidity, soil moisture, vegetation type, irrigation, and land management. These stomatal fluxes suggest that ambient O3 degrades biomass production and CO2 sequestration by 20%–24% at crop sites, 6%–29% at deciduous broadleaf forests, and 4%–20% at evergreen needleleaf forests in the United States and Europe.

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We have developed an accurate method (SynFlux) to estimate ozone deposition and stomatal uptake across 103 flux tower sites (43 US, 60 Europe), where ozone concentrations and fluxes have not been measured. In all, the SynFlux public dataset provides monthly values of ozone dry deposition for 926 site years across a wide array of ecosystems. The SynFlux dataset will promote further applications to ecosystem, air quality, or climate modeling across the geoscience community.
We have developed an accurate method (SynFlux) to estimate ozone deposition and stomatal uptake...