Field observations of Volatile Organic Compound (VOC) exchange in red oaks

Abstract

<p><strong>Abstract.</strong> Volatile organic compounds (VOCs) emitted by forests strongly affect the chemical composition of the atmosphere. While the emission of isoprenoids has been largely characterized, forests also exchange many oxygenated VOCs (oVOCs), including methanol, acetone, methyl ethyl ketone (MEK) and acetaldehyde, which are less well understood. We monitored total branch-level exchange of VOCs of a strong isoprene emitter (<i>Quercus rubra</i> L.) in a mixed forest in New England, where canopy-level fluxes of VOCs had been previously measured. We report daily exchange of several oVOCs and investigated unknown sources and sinks, finding several novel insights. In particular, we found that emission of MEK is linked to uptake of methyl vinyl ketone (MVK), a product of isoprene oxidation. The link was confirmed by corollary experiments proving in vivo detoxification of MVK, which is harmful to plants. Comparison of MEK, MVK and isoprene fluxes provided an indirect indication of within-plant isoprene oxidation. Furthermore, besides confirming bidirectional exchange of acetaldehyde, we also report for the first time direct evidence of benzaldehyde bidirectional exchange in forest plants. Net emission or deposition of benzaldehyde was found in different periods of measurements, indicating an unknown foliar sink that may influence atmospheric concentrations. Other VOCs, including methanol, acetone and monoterpenes, showed clear daily emission trends, but no deposition. Measured VOC emission and deposition rates were generally consistent with their ecosystem-scale flux measurements at a nearby site.</p>

Transpiration directly regulates the emissions of water‐soluble short‐chained OVOCs

“…In addition, especially emissions of acetaldehyde have been detected to depend on ambient acetaldehyde concentration so that when a certain compensation point (ranging between 0 and 8.5 ppbv) in ambient concentration is reached, there is more uptake than emissions by the leaves (Capellin et al, ; Cojocariu et al, ; Filella, Peñuelas, & Seco, ; Jardine et al, ; Karl, 2005; Kesselmeier et al, 2001). Cojocariu et al () report uptake of acetone in cool temperatures (below 4.6 °C) when its ambient concentration is 2.8–4 ppbv but also state that there is no known uptake mechanism for acetone.…”

“…Cojocariu et al () report uptake of acetone in cool temperatures (below 4.6 °C) when its ambient concentration is 2.8–4 ppbv but also state that there is no known uptake mechanism for acetone. Metabolism of methanol has been detected in plants (Fall, ; Gout, 2000; Kreuzwieser et al, ), but the compensation point can be as high as 15–45 ppbv (Capellin et al, ). The ambient concentrations at our study site during growing seasons are in the very low end of reported compensation point values, approximately 0.2–0.5 ppbv for acetaldehyde, 0.5–2.5 ppbv for acetone, and 0.2–4 ppbv for methanol (Lappalainen et al, ).…”

Process Understanding of Soil BVOC Fluxes in Natural Ecosystems: A Review

“…Combining EC with PTR‐MS can average over the heterogenic area and provide ecosystem‐level fluxes for a continuous period (Park et al, ; Ruuskanen et al, ). However, EC measurements cover the whole ecosystem and the measured flux cannot separate between vegetation and soil emissions (Cappellin et al, ; Karl et al, ; Park et al, ). Together with continuous measurements from soil chambers, it might be possible to distinguish soil fluxes from vegetation.…”

Evidence for an Oceanic Source of Methyl Ethyl Ketone to the Atmosphere

“…The sources of MEK are not fully understood (Yañez-Serrano et al, 2016). Known sources of MEK include direct emissions from biomass burning and the terrestrial biosphere, as well as secondary production from the oxidation of anthropogenic alkanes (Cappellin et al, 2016;Jordan et al, 2009;Yañez-Serrano et al, 2016). Better quantification of the sources of MEK is needed to constrain the abundances, seasonality, and transport of MEK throughout the atmosphere (Chen et al, 2019).…”