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Volume 15, issue 15
Atmos. Chem. Phys., 15, 8559–8576, 2015
https://doi.org/10.5194/acp-15-8559-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Chem. Phys., 15, 8559–8576, 2015
https://doi.org/10.5194/acp-15-8559-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 03 Aug 2015

Research article | 03 Aug 2015

Relationships between photosynthesis and formaldehyde as a probe of isoprene emission

Y. Zheng1, N. Unger1,2, M. P. Barkley3, and X. Yue2 Y. Zheng et al.
  • 1Department of Geology and Geophysics, Yale University, New Haven, Connecticut 06511, USA
  • 2School of Forestry and Environmental Studies, Yale University, New Haven, Connecticut 06511, USA
  • 3EOS group, Department of Physics and Astronomy, University of Leicester, Leicester, UK

Abstract. Atmospheric oxidation of isoprene emission from land plants affects radiative forcing of global climate change. There is an urgent need to understand the factors that control isoprene emission variability on large spatiotemporal scales but such direct observations of isoprene emission do not exist. Two readily available global-scale long-term observation-based data sets hold information about surface isoprene activity: gross primary productivity (GPP) and tropospheric formaldehyde column variability (HCHOv). We analyze multi-year seasonal linear correlations between observed GPP and HCHOv. The observed GPP–HCHOv correlation patterns are used to evaluate a global Earth system model that embeds three alternative leaf-level isoprene emission algorithms. GPP and HCHOv are decoupled in the summertime in the southeast US (r=−0.03). In the Amazon, GPP and HCHOv are weakly correlated in March-April-May (MAM), correlated in June-July-August (JJA) and weakly anticorrelated in September-October-November (SON). Isoprene emission algorithms that include soil moisture dependence demonstrate greater skill in reproducing the observed interannual seasonal GPP–HCHOv correlations in the southeast US and the Amazon. In isoprene emission models that include soil moisture dependence, isoprene emission is correlated with photosynthesis and anticorrelated with HCHOv. In an isoprene emission model without soil moisture dependence, isoprene emission is anticorrelated with photosynthesis and correlated with HCHOv. Long-term monitoring of isoprene emission, soil moisture and meteorology is required in water-limited ecosystems to improve understanding of the factors controlling isoprene emission and its representation in global Earth system models.

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We apply two global observational data sets, gross primary productivity (GPP) and tropospheric formaldehyde column variability (HCHOv), to probe isoprene emission variability on large spatiotemporal scales. GPP and HCHOv are decoupled or weakly anticorrelated in regions and seasons when isoprene emission is high. Isoprene emission models that include soil moisture dependence demonstrate greater skill in reproducing observed seasonal GPP-HCHOv correlations in the southeast US and the Amazon.
We apply two global observational data sets, gross primary productivity (GPP) and tropospheric...
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