Citation:

Sillman, S., F. Marsik, K. I. AlWali, M S. Landis, AND G. J. Keeler. MODELING THE ATMOSPHERE FORMATION OF REACTIVE MERCURY IN FLORIDA AND THE GREAT LAKES. Presented at American Geophysical Union's Fall Meeting, San Francisco, CA, December 13-17, 2004.

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:

Reactive mercury in the troposphere is affected by a complex mix of local emissions, global-scale transport, and gas and aqueous-phase chemistry. Here, we describe a modified version of the EPA model for urban/regional air quality (CMAQ) to include the chemistry of mercury, and model applications focusing on the Great Lakes region and on South Florida. The University of Michigan modifications to CMAQ include an integrated numerical solver for gas-phase and aqueous photochemistry, improved representation of in-cloud photolysis rates, and up-to-date reaction schemes for mercury chemistry. Reactive mercury is produced primarily by gas-phase reactions. Aqueous reactions tend to convert reactive mercury back to its elemental form, but the most important aqueous reactions (with HO₂ and O_2-) are problematic (Gartfeld and Jonnson, 2003). Model results suggest that gas-phase conversion from elemental to reactive mercury can lead to high concentrations of reactive mercury in the middle troposphere. Reactive mercury in the lower troposphere is removed more rapidly through both wet and dry deposition and potentially through aqueous conversion to elemental mercury. Model results are compared with a suite of comprehensive gas and aerosol measurements performed in Michigan and during aircraft measurements in S. Florida. Model results suggest that direct emission of reactive mercury contribute to atmospheric deposition in source regions.

Although this work was reviewed by EPA and approved for publication, it may not necessarily reflect official Agency policy.

Record Details: