Citation:

Landis, M S. AND R. K. STEVENS. THE MONITORING AND MODELING OF MERCURY SPECIES IN SUPPORT OF LOCAL, REGIONAL, AND GLOBAL MODELING. Presented at Harmonization of Mercury Measurement Methods and Models, Maratea, Italy, May 23-26, 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:

Cyrill Brosset, as early as 1979, recognized through research on the chemical forms of mercury in rain and in the air in Sweden and the Baltic States that (i) coal fired utility boilers in Eastern Europe were sources of mercury contaminating lakes in Sweden, and (ii) that both elemental and mercury halides (e.g., HgCl2) were being transported to these sites. His methods of measuring the various forms of mercury, were at the time extremely innovative, but required at least 24 hour sampling and subsequent complex laboratory analysis. Brosset recognized at that time a need to speiciate the forms of mercury being emitted from power plants and incinerators and the importance of developing near real time atmospheric mercury measurements.

It was not until the late 1990's that reliable techniques for speciation of mercury emissions and ambient air became available. Subsequent field studies confirmed Brosset's earlier work that, indeed, fossil fueled combustion sources emit both elemental and divalent forms of mercury, referred to as reactive gaseous mercury (RGM). RGM in stack emissions is most likely in the form of mercuric chloride (HgCl2). Atmospheric mercury studies in the Florida Everglades and Great Lakes during the 1990's demonstrated the relative importance of RGM dry deposition as a significant contributor of total mercury loading to these aquatic ecosystems. More recent studies including aircraft measurements off the coast of Florida (60-3500 m), at the Mauna Loa high altitude research station (3500 m), and in the Polar regions have shown elemental mercury is oxidized into RGM and particulate phase mercury via halide/photochemical reactions.

Since a significant portion of the atmospheric chemistry of mercury is poorly understood, contemporary atmospheric mercury models do not adequately simulate halide oxidation mechanisms observed in during polar mercury depletion events or in the marine free troposphere. This reality coupled to a lack of a comprehensive global emissions inventory that includes speciated anthropogenic and natural mercury sources limit the present reliability of deterministic models in predicting atmospheric behavior and deposition of mercury over short temporal and large spatial scales. To investigate the transport and deposition of atmospheric mercury and to elucidate the local, regional and global impact of industrial emissions, appropriate source and receptor site chemical monitoring and characterization is required.

The purpose of this paper is to provide information on contemporary mercury speciation and associated air quality monitoring methodologies required to generate the data necessary to conduct a robust source apportionment/receptor modeling study.

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

Record Details: