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

  • Author(s): DiGangi, J. P
  • Boyle, E. S
  • Karl, T.
  • Harley, P.
  • Turnipseed, A.
  • Kim, S.
  • Cantrell, C.
  • Maudlin III, R. L
  • Zheng, W.
  • Flocke, F.
  • Hall, S. R
  • Ullmann, K.
  • Nakashima, Y.
  • Paul, J. B
  • Wolfe, G. M
  • Desai, A. R
  • Kajii, Y.
  • Guenther, A.
  • Keutsch, F. N
  • 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.

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