1 ELIMINATING A NEED FOR THE DENSITY CORRECTIONS IN CO 2 AND H 2 O EDDY FLUXES WHEN USING FAST MIXING RATIO FROM AN ENCLOSED LOW- POWER GAS ANALYZER George Burba (1), Andres Schmidt (2), Russell Scott (3), Gerardo Fratini (1), Chad Hanson (2), James Kathilankal (1), Beverly Law (2), Dayle McDermitt (1), Robert Eckles (1), Michael Velgersdyk (1) (1) LI-COR Biosciences, Lincoln, NE, United States. (2) College of Forestry, Oregon State University, Corvallis, OR, United States. (3) Agricultural Research Service, USDA, Tucson, AZ, United States. george.burba@licor.com Enclosed gas analyzer with short intake tube is a blend of a traditional long-tube closed-path design and a traditional open-path design. Analogous to closed-path, the enclosed design leads to minimal data loss during precipitation events and icing, and it does not have surface heating issues. Analogous to the open-path design, the enclosed design has good frequency response due to the short intake tube, does not require frequent calibration, needs minimal maintenance, and could be low power when used with short intake tube. In addition to these advantages, enclosed design could provide measurement of fast mixing ratio, or dry mole fraction, because native density measurements can be converted to mixing ratio units using fast measurements of temperature, water vapor and pressure inside the sampling cell. Fast mixing ratio implies that the thermal expansion and water dilution of the sampled air have been accounted for in such a conversion. Thus, no density corrections are required to compute fluxes when the fast mixing ratio is used. Such a way of calculating fluxes has been used frequently with traditional closed-path analyzers (e.g., LI-6262 and LI-7000), because fast fluctuations in the air temperature of the sample were attenuated in the long intake tube, and because water vapor was simultaneously measured and dry mole fraction was output from the instrument. In an enclosed design, such as the LI-7200 used with short tube, most but not all of the fast temperature fluctuations are attenuated, so calculating fluxes using the mixing ratio output of such an instrument requires validation. The CO 2 and H 2 O Eddy Covariance fluxes of from eight experiments with new LI-7200 enclosed analyzer were examined here: five deployments of the Ameriflux Roving Intercomparison Station in California, Arizona, New Mexico and Oregon; one deployment at a USDA flux site in Arizona; and two deployments at the LI-COR flux test facility in Nebraska. Fluxes were computed in two ways: (i) via the traditional way using the density corrections, and (ii) via a mixing ratio output from the instrument without applying the density corrections. The results of these comparisons have important implications for future gas flux measurements, because avoiding half-hourly or hourly density corrections could help to minimize at least two kinds of uncertainties: (i) the uncertainties associated with correcting the product of fast covariances of gas density using sensible and latent heat flux calculated over half-hour or an hour; and (ii) the uncertainties in the magnitudes of the sensible and latent heat fluxes used in correcting gas flux.