ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-9-981-2009 The use of disjunct eddy sampling methods for the determination of ecosystem level fluxes of trace gases Turnipseed A. A. 1 5 Pressley S. N. 2 Karl T. 1 5 Lamb B. 2 Nemitz E. 3 Allwine E. 2 Cooper W. A. 4 Shertz S. 5 Guenther A. B. 1 5 Atmospheric Chemistry Division, National Center for Atmospheric Research, P.O. Box 3000 Boulder, CO 80307, USA Dept. of Civil and Environmental Engineering, Washington State University, Pullman, WA, USA Center for Ecology and Hydrology (CEH), Edinburgh, UK Earth Observing Laboratory, National Center for Atmospheric Research, P.O. Box 3000 Boulder, CO 80307, USA The Institute for Integrative and Multidisciplinary Earth Studies (TIIMES), National Center for Atmospheric Research, P.O. Box 3000 Boulder, CO 80307, USA 09 02 2009 9 3 981 994 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/9/981/2009/acp-9-981-2009.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/9/981/2009/acp-9-981-2009.pdf

The concept of disjunct eddy sampling (DES) for use in measuring ecosystem-level micrometeorological fluxes is re-examined. The governing equations are discussed as well as other practical considerations and guidelines concerning this sampling method as it is applied to either the disjunct eddy covariance (DEC) or disjunct eddy accumulation (DEA) techniques. A disjunct eddy sampling system was constructed that could either be combined with relatively slow sensors (response time of 2 to 40 s) to measure fluxes using DEC, or could also be used to accumulate samples in stable reservoirs for later laboratory analysis (DEA technique). Both the DEC and DEA modes of this sampler were tested against conventional eddy covariance (EC) for fluxes of either CO<sub>2</sub> (DEC) or isoprene (DEA). Good agreement in both modes was observed relative to the EC systems. However, the uncertainty in a single DEA flux measurement was considerable (~40%) due to both the reduced statistical sampling and the analytical precision of the concentration difference measurements. We have also re-investigated the effects of nonzero mean vertical wind velocity on accumulation techniques as it relates to our DEA measurements. Despite the higher uncertainty, disjunct eddy sampling can provide an alternative technique to eddy covariance for determining ecosystem-level fluxes for species where fast sensors do not currently exist.

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