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

Abstract

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.

Eddy covariance emission and deposition flux measurements using proton transfer reaction – time of flight – mass spectrometry (PTR-TOF-MS): comparison with PTR-MS measured vertical gradients and fluxes

“…Co-spectra of w (m/z 59.048) , w (m/z 61.027) , w (m/z 81.070) , and w (m/z 93.069) show some negative values (closed symbols) at high frequency above 0.3 Hz, and this may indicate complex processes within and/or above the canopy such as fast photochemical loss/production oxidizing BVOC with wake turbulence production. A similar phenomenon was observed in other studies for peroxyacetyl nitrate and formaldehyde (Wolfe et al, 2009;DiGangi et al, 2011). For the co-spectrum of w (m/z 61.027) , loss of flux signal is apparent as successive fall-off of signal at frequencies around ∼ 0.06 Hz.…”

Boreal forest BVOC exchange: emissions versus in-canopy sinks

“…In addition to emission and dry deposition, acetaldehyde, methanol, acetone, and formaldehyde can be chemically produced from the oxidation of other BVOCs and destroyed via OH oxidation or photolysis (Millet et al, 2010;Jacob et al, 2005;Khan et al, 2015;DiGangi et al, 2011). The chemical production and removal cancel out each other, which can finally result in negligible net chemical effect as shown in this study (Fig.…”

A new airborne laser-induced fluorescence instrument for in situ detection of formaldehyde throughout the troposphere and lower stratosphere

“…Photochemical degradation of anthropogenic and biogenic hydrocarbons greatly enhances HCHO production in the lower troposphere, with the most significant precursor being biogenic hydrocarbon isoprene. HCHO is also emitted through fuel combustion (Olaguer et al, 2009;Luecken et al, 2012), biomass burning (Yokelson et al, 2013) and vegetation (DiGangi et al, 2011). These sources are generally minor globally compared to secondary production, but they may be significant locally.…”