Air/surface exchange of mercury vapor in forests: Recent results of micrometeorological and chamber studies at Walker Branch watershed

Conference · Sat Dec 31 04:00:00 EST 1994

OSTI ID:49600

Lindberg, S E; Hanson, P J; Kim, K; Meyers, T P ^[1]

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1. Oak Ridge National Lab., TN (United States). Environmental Sciences Division

Atmospheric sources are recognized to be significant in the cycling of Hg in the biosphere, yet there are no reliable data on air/surface exchange rates of Hg in temperate forests. Project MASE (Mercury Air/Surface Exchange) involves development of field and laboratory techniques for measuring exchange rates for vapor-phase Hg in forests. The authors summarize here the development and application of a tower-based micrometeorological method for Hg fluxes over forest soils and vegetation, and comparisons of these results with data from a controlled-environment chamber. The modified Bowen ratio (MBR) method has been applied to fluxes of other trace gases in forests and involves quantification of the concentration gradients of Hg and of gam over the surface of interest. The gradients of CO{sub 2} and H{sub 2}O are combined with direct measurements of their fluxes measured by W-response sensors and eddy correlation to compute turbulent mixing coefficients. These are used with the measured gradients of Hg to estimate fluxes. The authors developed a sampler which uses 12 replicate mass flow controllers to measure air concentrations of Hg vapor with the precision and accuracy necessary for quantifying concentration gradients over the forest. They consistently achieve a precision of < 1--2% for 1--2 h samples of Hg in air at background levels. They also designed a dynamic plant exposure chamber to measure Hg fluxes to soils and tree seedlings over a wide range of concentrations. The authors tested the MBR method over Hg-contaminated soils with excellent success (the data behaved as predicted from first principals). During 1993 they measured concentration gradients of Hg from a 44 m tower over a mature forest canopy in Oak Ridge, TN and from a 3 m mast over forest soils.

• OSTI ID: 49600
• Report Number(s): CONF-9410273--
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
AIR SAMPLERS
AIR-BIOSPHERE INTERACTIONS
DESIGN
ECOLOGICAL CONCENTRATION
EXPOSURE CHAMBERS
MERCURY
MONITORING
OAK RIDGE RESERVATION
POLLUTION
WATERSHEDS