The use of relaxed eddy accumulation to measure biosphere-atmosphere exchange of isoprene and other biological trace gases

Canopy level flux measurements of 2-methyl-3-buten-2-ol (MBO), acetone, and methanol were made over a subalpine forest in the Rocky Mountains in Colorado in the summer of 1999. The measurements were carried out using a portable relaxed eddy accumulation system that collected samples on adsorbent cartridges. Midday fluxes of acetone were highest at ∼2.5 mg of C m -2 h -1 . Methanol and MBO fluxes were ∼1.0 mg of C m -2 h -1 each. These fluxes occurred with average daytime high temperatures of only 18°C. Diurnal fluxes of MBO were strongly correlated with light and temperature. Acetone and methanol did not have simple diurnal patterns. These results indicate that oxygenated volatile organic compounds may make a significant contribution to the flux of reactive carbon to the atmosphere in western U.S. pine forests.

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“…The REA technique has been used to measure biogenic VOC fluxes in the past (24)(25)(26)18). There are two basic system designs.…”

Section: Methodsmentioning

confidence: 99%

Canopy Level Fluxes of 2-Methyl-3-buten-2-ol, Acetone, and Methanol by a Portable Relaxed Eddy Accumulation System

Baker

Guenther

Greenberg

et al. 2001

Environ. Sci. Technol.

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“…Eddy-covariance measurements of CO 2 can be biased at night too. Often, an eddy-covariance system will not measure the CO 2 efflux respired by soil, leaves, and Bowling et al (1998). The isoprene-emitting biomass value of 145 g m Ϫ2 was calculated using a distance-weighting function that was derived from a numerical footprint model.…”

Section: Resultsmentioning

confidence: 99%

“…Flux densities of isoprene between the canopy and the atmosphere were measured using the eddy-covariance and relaxed eddy accumulation (REA) methods (Bowling et al 1998). The eddy-covariance method employed a three-dimensional sonic anemometer (model SAT-211/3K, Applied Technology, Boulder, CO) and an ozone-induced chemiluminesence instrument (FIS, Hills Scientific, Boulder, CO).…”

Section: Measurementsmentioning

confidence: 99%

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Scaling Isoprene Fluxes from Leaves to Canopies: Test Cases over a Boreal Aspen and a Mixed Species Temperate Forest

et al. 1999

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The rate at which isoprene is emitted by a forest depends on an array of environmental variables, the forest's biomass, and its species composition. At present it is unclear whether errors in canopy-scale and process-level isoprene emission models are due to inadequacies in leaf-to-canopy integration theory or the imperfect assessment of the isoprene-emitting biomass in the flux footprint. To address this issue, an isoprene emission model (CAN-VEG) was tested over a uniform aspen stand and a mixed-species, broad-leaved forest.The isoprene emission model consists of coupled micrometeorological and physiological modules. The micrometeorological module computes leaf and soil energy exchange, turbulent diffusion, scalar concentration profiles, and radiative transfer through the canopy. Environmental variables that are computed by the micrometeorological module, in turn, drive physiological modules that calculate leaf photosynthesis, stomatal conductance, transpiration and leaf, bole and soil/root respiration, and rates of isoprene emission.The isoprene emission model accurately predicted the diurnal variation of isoprene emission rates over the boreal aspen stand, as compared with micrometeorological flux measurements. The model's ability to simulate isoprene emission rates over the mixed temperate forest, on the other hand, depended strongly upon the amount of isoprene-emitting biomass, which, in a mixed-species forest, is a function of the wind direction and the horizontal dimensions of the flux footprint. When information on the spatial distribution of biomass and the flux footprint probability distribution function were included, the CANVEG model produced values of isoprene emission that compared well with micrometeorological measurements. The authors conclude that a mass and energy exchange model, which couples flows of carbon, water, and nutrients, can be a reliable tool for integrating leaf-scale, isoprene emission algorithms to the canopy dimension over dissimilar vegetation types as long as the vegetation is characterized appropriately.

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“…Integrating volumes (known also as buffer volumes) have been used in previous studies to dampen temporal fluctuations in trace gas mole fractions for flux-gradient measurements (Griffith et al, 2002), for contributions of advection (Yi et al, 2008), and for flask sampling (Bowling et al, 2003). A block-averaging effect is accomplished in flux-gradient measurements that trap the compound of interest over periods of minutes or hours (Müller et al, 1993;Goldstein et al, 1995Goldstein et al, , 1996Goldstein et al, , 1998Meyers et al, 1996) and eddy accumulation methods that use high-precision differential collection apparatus to trap and then sample air from upand down-drafts to determine the flux (Businger and Onlcey, 1990;Guenther et al, 1996;Bowling et al, 1998).…”

Section: Sampling Errormentioning

confidence: 99%

Ecosystem fluxes of hydrogen: a comparison of flux-gradient methods

et al. 2014

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Abstract. Our understanding of biosphere-atmosphere exchange has been considerably enhanced by eddy covariance measurements. However, there remain many trace gases, such as molecular hydrogen (H 2 ), that lack suitable analytical methods to measure their fluxes by eddy covariance. In such cases, flux-gradient methods can be used to calculate ecosystem-scale fluxes from vertical concentration gradients. The budget of atmospheric H 2 is poorly constrained by the limited available observations, and thus the ability to quantify and characterize the sources and sinks of H 2 by fluxgradient methods in various ecosystems is important. We developed an approach to make nonintrusive, automated measurements of ecosystem-scale H 2 fluxes both above and below the forest canopy at the Harvard Forest in Petersham, Massachusetts, for over a year. We used three flux-gradient methods to calculate the fluxes: two similarity methods that do not rely on a micrometeorological determination of the eddy diffusivity, K, based on (1) trace gases or (2) sensible heat, and one flux-gradient method that (3) parameterizes K. We quantitatively assessed the flux-gradient methods using CO 2 and H 2 O by comparison to their simultaneous independent flux measurements via eddy covariance and soil chambers. All three flux-gradient methods performed well in certain locations, seasons, and times of day, and the best methods were trace gas similarity for above the canopy and K parameterization below it. Sensible heat similarity required several independent measurements, and the results were more variable, in part because those data were only available in the winter, when heat fluxes and temperature gradients were small and difficult to measure. Biases were often observed between flux-gradient methods and the independent flux measurements, and there was at least a 26 % difference in nocturnal eddy-derived net ecosystem exchange (NEE) and chamber measurements. H 2 fluxes calculated in a summer period agreed within their uncertainty and pointed to soil uptake as the main driver of H 2 exchange at Harvard Forest, with H 2 deposition velocities ranging from 0.04 to 0.10 cm s −1 .

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The use of relaxed eddy accumulation to measure biosphere-atmosphere exchange of isoprene and other biological trace gases

Cited by 99 publications

References 55 publications

Canopy Level Fluxes of 2-Methyl-3-buten-2-ol, Acetone, and Methanol by a Portable Relaxed Eddy Accumulation System

Canopy Level Fluxes of 2-Methyl-3-buten-2-ol, Acetone, and Methanol by a Portable Relaxed Eddy Accumulation System

Scaling Isoprene Fluxes from Leaves to Canopies: Test Cases over a Boreal Aspen and a Mixed Species Temperate Forest

Ecosystem fluxes of hydrogen: a comparison of flux-gradient methods

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