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DEPOSITION AND EMISSION OF GASEOUS MERCURY TO AND FROM LAKE MICHIGAN DURING THE LAKE MICHIGAN MASS BALANCE STUDY (JULY, 1994 - OCTOBER, 1995)
Citation:
Vette, A F., M S. Landis, AND G. J. Keeler. DEPOSITION AND EMISSION OF GASEOUS MERCURY TO AND FROM LAKE MICHIGAN DURING THE LAKE MICHIGAN MASS BALANCE STUDY (JULY, 1994 - OCTOBER, 1995). ENVIRONMENTAL SCIENCE & TECHNOLOGY 36(21):4525-4532, (2002).
Impact/Purpose:
The overall research objective of this task is to improve our understanding of the emission, transport, transformation, and deposition of atmospheric mercury. Information garnered from this research is used to improve and evaluate EPA deterministic models that are used to investigate the (i) relative impact to local, regional, and global sources to atmospheric mercury deposition, and (ii) benefits of various emission reduction scenarios.
Specifically, individual research project objectives are listed below:
(1) Evaluate the ability of speciated mercury (Hg0, Hg2+, HgP) measurements to aid source apportionment models in identifying anthropogenic source contributions to atmospheric mercury deposition
(2) Elucidate the contribution of coal combustion sources to observed mercury wet deposition in the Ohio River Valley
(3) Obtain atmospheric profiles (200 - 12,000 ft) of speciated ambient mercury off the south Florida Coast
- Evaluate the role of long range transport of RGM to Florida in the marine free troposphere.
- Identify any vertical mercury gradients that might indicate the presence of rapid mercury chemistry in air or in cloud water.
(4) Conduct research at Mauna Loa Observatory to elucidate elemental mercury oxidation in the remote marine free troposphere.
(5) Conduct laboratory kinetics experiments to determine the rate constants of elemental mercury oxidation to gaseous inorganic divalent mercury species from atmospheric halide species (e.g. BrO, ClO).
Description:
This paper presents measurements of dissolved gaseous mercury (DGM) concentrations in Lake Michigan and the application of a mechanistic approach to estimate deposition and emission fluxes of gaseous mercury (Hg2+ and Hg0) to and from Lake Michigan. Measurements of DGM concentrations made during May and July, 1994 and January, 1995 indicate that Lake Michigan was supersaturated with DGM suggesting that transfer of Hg0 occurs from the water to the atmosphere. Over-water concentrations of gaseous Hg2+ were estimated from total gaseous Hg (TGM) concentrations measured at five sites in the basin and used to model dry deposition fluxes of Hg2+. The modeling approach combines estimates of dry deposited Hg2+ with known photochemical and biotic reduction rates to form Hg0, which is available for re-emission. The model accounts for temporal and spatial variations in the deposition velocity of gaseous Hg2+ and the transfer velocity of Hg0 using high temporal and spatial resolution meteorological data. The modeled DGM concentrations agree well with the observed DGM concentrations in Lake Michigan. The modeled dry deposition fluxes of Hg2+ (286-797 kg yr-1) are very similar to the emission fluxes of Hg0 (320-959 kg yr-1), depending on the gaseous Hg2+ concentration used in the model.
The U.S. Environmental Protection Agency through its Office of Research and Development funded the research described here under cooperative agreement # CR820909-01 and its Great Lakes National Programs Office under grant # GL995569-01 to the University of Michican Air Quality Laboratory. It has been subjected to Agency review and approved for publication. Mention of trade names or commercial products does not constitute an endorsement or recommendation for use.