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Development, evaluation and application of a modified micrometeorological gradient method for long-term estimation of gaseous dry deposition over forest canopies.
Citation:
Wu, Z., Johnt Walker, AND L. Zhang. Development, evaluation and application of a modified micrometeorological gradient method for long-term estimation of gaseous dry deposition over forest canopies. Presented at Ozone Dry Deposition: Constraints from multiplatform observations and multi-scale modeling, Palisades, CA, October 05 - 06, 2017.
Impact/Purpose:
Long-term datasets are needed to better understand the effects of ozone deposition on ecosystem health. While short-term studies are useful for examining deposition processes and improving flux algorithms, long-term datasets are needed to understand interactions between trends in atmospheric chemistry and climate and their effects on deposition processes and ecosystem response. Cost-effective measurement methods suitable for routine long-term operation are needed to develop such datasets.
Description:
Small pollutant concentration gradients between levels above a plant canopy result in large uncertainties in estimated air–surface exchange fluxes when using existing micrometeorological gradient methods, including the aerodynamic gradient method (AGM) and the modified Bowen ratio method (MBR). A modified micrometeorological gradient method (MGM) has been developed for estimating O3 dry deposition fluxes over a forest canopy using concentration gradients between a level above and a level below the canopy top, taking advantage of relatively large gradients between these levels due to significant pollutant uptake in the top layers of the canopy. The new method is compared with the AGM and MBR methods and is also evaluated using eddy-covariance (EC) flux measurements collected at the Harvard Forest Environmental Measurement Site, Massachusetts, during 1993–2000. The MGM method being the closest in magnitude to the EC measurements. The new method provides an alternative approach to monitoring/estimating long-term deposition fluxes of similar pollutants over tall canopies. This presentation also presents plans for establishment of Duke Forest as a new long-term measurement site for ozone fluxes.