Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 8 4 2008 10.5194/acpd-8-13413-2008 http://www.atmos-chem-phys-discuss.net/8/13413/2008/ http://www.atmos-chem-phys-discuss.net/8/13413/2008/acpd-8-13413-2008.html http://www.atmos-chem-phys-discuss.net/8/13413/2008/acpd-8-13413-2008.pdf 13413 13451 2008-07-15 The use of disjunct eddy sampling methods for the determination of ecosystem level fluxes of trace gases. A. A. Turnipseed S. N. Pressley T. Karl B. Lamb E. Nemitz E. Allwine W. A. Cooper S. Shertz A. B. Guenther Atmospheric Chemistry Div., National Center for Atmospheric Research, Boulder, CO, USA Dept. of Civil and Environmental Engineering, Washington State Univ., Pullman, WA, USA Center for Ecology and Hydrology (CEH), Edinburgh, UK Earth Observing Laboratory, National Center for Atmospheric Research, Boulder, CO, USA The Institute for Integrative and Multidisciplinary Earth Studies (TIIMES), National Center for Atmospheric Research, Boulder, CO, USA 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 CO₂ (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. 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