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United States Department of Agriculture

Agricultural Research Service

Title: Conditional Sampling for Measuring Mercury Vapor Fluxes

Authors
item Cobos, Douglas - UNIVERSITY OF MINNESOTA
item Baker, John
item Nater, Edward - UNIVERSITY OF MINNESOTA

Submitted to: Atmospheric Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 28, 2002
Publication Date: N/A

Interpretive Summary: Mercury, a volatile metal, is widely distributed atmospherically, and is thus deposited in areas remote from local pollution sources. This ease of transport complicates identification of anthropogenic and natural source areas. Once in the environment, mercury readily bio-accumulates in aquatic systems to the potentially harmful levels in fish and other top predators. This has caused regulatory agencies in Minnesota (and other states) to pos fish consumption advisories for lakes far-removed from potential pollution sources. To remedy this problem, sources of mercury to the atmosphere must be determined. To this point, surface-air mercury fluxes have been measured mainly with small chamber techniques, which require extensive scaling and extrapolation to yield field scale flux estimates. We have developed a conditional sampling system for measuring mercury fluxes at the field scale. In this initial measurement campaign, we measured mercury fluxes from non-contaminated agricultural soil. We found the flux rates t be in good agreement with published values over similar surfaces. These measurements along with subsequent measurements to be taken over amended and contaminated soils will allow regulatory agencies to make informed decisions and regulations concerning soil amendments.

Technical Abstract: Surface-atmosphere mercury fluxes are difficult to measure accurately. Current techniques include dynamic flux chambers and micrometeorological gradient and aerodynamic approaches, all of which have a number of intrinsic problems associated with them. We have adapted conditional sampling (relaxed eddy accumulation), a micrometeorological technique commonly used to measure other trace gas fluxes, to measure surface - air mercury fluxes. Our initial flux measurement campaign over an agricultural soil consisted of two one-week measurement periods, and was longer in duration than any previously reported mercury flux measurement periods. Fluxes during both measurement periods ranged between 98.2 ng m**-2 h**-1 (evolution) and -32.7 ng m**-2 h**-1 (deposition) with an average evolution of 6.3 ng m**-2 h**-1. The data showed significant diurnal trends, weakly correlated with shallow soil temperatures and solar radiation. This initial trial run indicates that conditional sampling has much promise for the accurate quantification of both short and long-term mercury fluxes.

Last Modified: 10/23/2014