1Department of Chemistry, University of Wisconsin-Madison, Madison, WI, USA
2Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, CO, USA
3Department of Physics, University of Helsinki, Finland
4Thermo Fisher Scientific, Redwood City, CA, USA
5Department of Atmospheric & Oceanic Sciences, University of Wisconsin-Madison, Madison, WI, USA
6Division of Applied Chemistry, Faculty of Urban Environmental Sciences, Tokyo Metropolitan University, Japan
*now at: Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, CO, USA
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.