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First direct measurements of formaldehyde flux via eddy covariance: Implications for missing in-canopy formaldehyde sources

  • Author(s): Digangi, JP;
  • Boyle, ES;
  • Karl, T;
  • Harley, P;
  • Turnipseed, A;
  • Kim, S;
  • Cantrell, C;
  • Maudlin, RL;
  • Zheng, W;
  • Flocke, F;
  • Hall, SR;
  • Ullmann, K;
  • Nakashima, Y;
  • Paul, JB;
  • Wolfe, GM;
  • Desai, AR;
  • Kajii, Y;
  • Guenther, A;
  • Keutsch, FN
  • et al.
Abstract

We report the first observations of formaldehyde (HCHO) flux measured via eddy covariance, as well as HCHO concentrations and gradients, as observed by the Madison Fiber Laser-Induced Fluorescence Instrument during the BEACHON-ROCS 2010 campaign in a rural, Ponderosa Pine forest northwest of Colorado Springs, CO. A median noon upward flux of ∼80 μg m-2 h-1 (∼24 pptv m s-1) was observed with a noon range of 37 to 131 μg m-2 h-1. Enclosure experiments were performed to determine the HCHO branch (3.5 μg m-2 h-1) and soil (7.3 μg m-2 h-1) direct emission rates in the canopy. A zero-dimensional canopy box model, used to determine the apportionment of HCHO source and sink contributions to the flux, underpredicted the observed HCHO flux by a factor of 6. Simulated increases in concentrations of species similar to monoterpenes resulted in poor agreement with measurements, while simulated increases in direct HCHO emissions and/or concentrations of species similar to 2-methyl-3-buten-2-ol best improved model/measurement agreement. Given the typical diurnal variability of these BVOC emissions and direct HCHO emissions, this suggests that the source of the missing flux is a process with both a strong temperature and radiation dependence. © 2011 Author(s).

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