Observations of elevated formaldehyde over a forest canopy suggest missing sources from rapid oxidation of arboreal hydrocarbons

Abstract

Abstract.To better understand the processing of biogenic VOCs (BVOCs) in the pine forests of the US Sierra Nevada, we measured HCHO at Blodgett Research Station using Quantum Cascade Laser Spectroscopy (QCLS) during the Biosphere Effects on Aerosols and Photochemistry Experiment (BEARPEX) of late summer 2007. Four days of the experiment exhibited particularly copious HCHO, with midday peaks between 15-20 ppbv, while the other days developed delayed maxima between 8-14 ppbv in the early evening. From the expansive photochemical data set, we attempt to explain the observed HCHO concentrations by quantifying the various known photochemical production and loss terms in its chemical budget. Overall, known chemistry predicts a factor of 3-5 times less HCHO than observed. By examining diurnal patterns of the various budget terms we conclude that, during the high HCHO period, local, highly reactive oxidation chemistry produces an abundance of formaldehyde at the site. The results support the hypothesis of previous work at Blodgett Forest suggesting that large quantities of oxidation products, observed directly above the ponderosa pine canopy, Correspondence to: W. Choi (wschoi@ucdavis.edu) are evidence of profuse emissions of very reactive volatile organic compounds (VR-VOCs) from the forest. However, on the majority of days, under generally cooler and more moist conditions, lower levels of HCHO develop primarily influenced by the influx of precursors transported into the region along with the Sacramento plume.

DOAS measurements of formaldehyde and glyoxal above a south-east Asian tropical rainforest

“…However, none of these measurements were in tropical locations, where there should be a higher concentration of precursor species such as isoprene, with the exception of Huisman et al (2011) which had very similar isoprene concentrations and also high levels of the glyoxal precursor MBO. The formaldehyde measurements show good agreement with previous ground-based measurements in rural locations where mixing ratios of around 0.1-4 ppb have been recorded (Lee et al, 1998;Munger et al, 1995;Lowe and Schmidt, 1983;Heikes, 1992), and airborne measurements over the Amazon rainforest which were typically around 1-2 ppb (Stickler et al, 2007), although the peak concentrations are lower than those observed by Choi et al (2010) above a pine plantation which ranged from 15-20 ppb.…”

“…Concentrations of formaldehyde in rural locations are typically in the 0.1-4 ppb range (Munger et al, 1995;Lee et al, 1998;Heikes, 1992;Lowe and Schmidt, 1983), with much higher concentrations (up to 29 ppb) in urban locations (Possanzini et al, 2002;Grosjean, 1991). Measurements of HCHO above a pine forest in the US Sierra Nevada using Quantum Cascade Laser Spectroscopy (QCLS) showed elevated levels of 15-20 ppb at midday attributed to abundant emissions of very reactive volatile organic compounds (Choi et al, 2010).…”

Modeling of HCHO and CHOCHO at a semi-rural site in southern China during the PRIDE-PRD2006 campaign

“…But, during a chamber study, Kroll et al (2005) did not find any growth of both neutral ((NH 4 ) 2 SO 4 ) and acidic (NH 4 HSO 4 ) aerosols in the presence of gaseous HCHO, suggesting that the uptake of HCHO by aerosols is unlikely taking place. Although numerical simulations of HCHO, either by multi-dimensional models or box models, can in some cases reproduce HCHO observations (Wagner et al, 2001;Fried et al, 2003b;MacDonald et al, 2012), significant discrepancies between modeled and measured HCHO concentration have been frequently found (Choi et al, 2010;Fried et al, 2011, and references therein). The model underestimation can arise from the following: deviation from the steadystate assumption (Fried et al, 2003a), direct emissions and their transport (Fried et al, 2011), missing consideration of HCHO production from unmeasured precursors (Kormann et al, 2003;Choi et al, 2010), etc.…”

“…Although numerical simulations of HCHO, either by multi-dimensional models or box models, can in some cases reproduce HCHO observations (Wagner et al, 2001;Fried et al, 2003b;MacDonald et al, 2012), significant discrepancies between modeled and measured HCHO concentration have been frequently found (Choi et al, 2010;Fried et al, 2011, and references therein). The model underestimation can arise from the following: deviation from the steadystate assumption (Fried et al, 2003a), direct emissions and their transport (Fried et al, 2011), missing consideration of HCHO production from unmeasured precursors (Kormann et al, 2003;Choi et al, 2010), etc. If the steady-state assumption is disturbed, e.g., in the vicinity of fresh emissions, the model can also overpredict the measured HCHO concentration (Fried et al, 2011).…”

Methanol emissions from maize: Ontogenetic dependence to varying light conditions and guttation as an additional factor constraining the flux

“…Since it is an important precursor of carbon monoxide, formaldehyde and tropospheric ozone, it plays an important role in the global tropospheric chemistry (Tie et al, 2003;Millet et al, 2006;Duncan et al, 2007;Choi et al, 2010;Hu et al, 2011). Field and laboratory measurements have been carried out to characterize methanol sources and sinks.…”