Find in Library

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<sup>−2</sup> h<sup>−1</sup> (~24 ppt<sub>v</sub> m s<sup>−1</sup>) was observed with a noon range of 37 to 131 μg m<sup>−2</sup> h<sup>−1</sup>. Enclosure experiments were performed to determine the HCHO branch (3.5 μg m<sup>-2</sup> h<sup>−1</sup>) and soil (7.3 μg m<sup>−2</sup> h<sup>−1</sup>) 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.