U.S. Environmental Protection Agency
Office of Research and Development
National Center for Environmental Research
Science to Achieve Results (STAR) Program


Mercury: Transport, Transformation, and Fate in the Atmosphere

Opening Date:  April 20, 2001
Closing Date:   August 15, 2001

Objectives and priorities
Standard Instructions for Submitting an Application

Get Standard STAR Forms and Instructions
View NCER Research Capsules on mercury research
View research awarded under the previous mercury solicitation


The Clean Air Act, as amended in 1990, required the U.S. EPA to prepare an assessment of the magnitude of U.S. mercury emissions by source, the health and environmental effects of the emissions, and the cost and availability of control technologies. The resulting report entitled Mercury Study Report to Congress (https://www.epa.gov/oar/mercover.html) was published in December 1997. This report identified mercury as a human health and environmental problem needing additional scientific and technical research. Two subsequent Agency reports, Great Waters Third Report to Congress dated June 2000 and Decision to Regulate Mercury and Other Air Toxics Emitted from Power Plants dated December 2000 (both available at https://www.epa.gov/airlinks) stress the adverse impacts of mercury on both humans and wildlife.

Fish consumption is known to be the dominant pathway for exposure of humans and wildlife to mercury. It is also accepted that the majority of this mercury comes from atmospheric deposition.  The U.S. EPA’s Office of Research and Development (ORD) recently published its Mercury Research Strategy (https://www.epa.gov/ORD/NRMRL/mercury/).  This strategy guides ORD’s mercury research program through 2005.  An integral part of the strategy involves study of atmospheric mercury transport, transformation, and fate.

Mercury is a naturally occurring element that cycles between the atmosphere, land, and water.
Atmospheric mercury exists mostly in elemental gas form, but a variety of oxidized mercury compounds also occur.  Elemental mercury and some mercury compounds are gaseous at typical atmospheric conditions, but most mercury compounds are less volatile and exist in the atmosphere primarily as particulate matter. Some volatile mercury compounds can sorb to carbon-rich aerosols and exist simultaneously in both gaseous and particulate forms, resembling semi-volatile organic compounds.

Some gaseous mercury compounds are chemically reactive and/or water soluble.  This reactive gaseous mercury, commonly called “RGM,” is readily removed from the air by water surfaces, vegetation, or any other surface with which it may react. Conversely, elemental mercury gas is relatively inert and appears to stay in the atmosphere for many months, dispersing throughout the atmosphere before it is eventually removed.  Although elemental mercury is by far the most abundant form of mercury in air, its deposition is thought to be minor compared to that of reactive gaseous mercury and particulate mercury.  In fact, the slow removal of elemental mercury from air may be largely due to its transformation to other forms of mercury, rather than its deposition. Obviously, an assessment of atmospheric mercury transport and fate requires an accurate accounting of the chemical and physical forms of the mercury emitted.   It also follows that a reasonably complete understanding of chemical and physical transformations of mercury in air and cloud water is required.

The goal of this solicitation is to develop a better understanding of natural and anthropogenic emissions of mercury to air, and the atmospheric processes that affect the transport, transformation and deposition of those emissions.  The development of improved models of the emission, transport, transformation, and fate of mercury in the atmosphere is also desirable in order to estimate response to emission reductions.

There is some evidence that existing air emission inventories may not account for all of the mercury emitted from some sources (e.g., chlor-alkali plants), and other sources may have been overlooked due to a lack of information (e.g., oil refineries, metals recycling, and motor vehicles).  These emission inventories also lack information on the chemical and physical forms of mercury emitted.  Natural mercury emissions from volcanic and geothermal activity are episodic, and the more constant emissions from mercury-rich soils are not well surveyed.  It remains difficult to differentiate between truly natural emissions of mercury from soils and water bodies and the re-emission of anthropogenic mercury from industrial contamination.  Air emission inventories accounting for all sources of mercury need to be developed with spatial and temporal resolutions commensurate to the resolutions of the atmospheric simulation models that will use them.

Various chemical reactions of mercury have been identified in both the gaseous and aqueous phases, but the rate constants for many of these reactions are based on limited laboratory testing.  The rate constant for the reduction of aqueous mercuric sulfite (HgSO3) to elemental mercury by decomposition was recently re-evaluated and determined to be much slower than previously indicated, resulting in significant changes in cloud chemistry modeling results.  Research is needed to confidently determine rate constants for all chemical reactions believed to be important to atmospheric mercury in air and cloud water.  The same is true for the sorption of mercury to particulate matter in air and cloud water.  This phenomenon is suspected to be important to the reduction-oxidation balance of mercury in cloud water, but confident determinations of the sorbed fraction of mercury under various conditions do not exist.

Recent investigation of the episodic depletion of elemental mercury from air over the arctic in springtime has identified a rapid chemical transformation of elemental mercury to oxidized forms which appear to deposit rapidly to the snowpack.  At this time, the oxidizing agent(s) and the products of this reaction remain uncertain.  Also uncertain is the fraction of the mercury deposited to the snowpack that returns to the atmosphere when the snow melts.  This phenomenon suggests that elemental mercury may be more efficiently deposited from the atmosphere at arctic locations, much like semi-volatile organic compounds.  This could have serious implications for the eventual latitudinal distribution of past and present emissions of mercury as they continue in the global mercury cycle.  Research is needed to better understand this phenomenon and its implications for the global transport and deposition of mercury.


EPA is soliciting fundamental research to identify all important sources of mercury to the atmosphere, to develop emission inventories for all sources which include information on the physical and chemical forms of mercury emitted, to identify important chemical and physical transformations of mercury in air and cloud water, and to understand the processes leading to mercury deposition from the atmosphere, including dry deposition. The outcome of this research  will be useful for developing computer models capable of resolving source-receptor relationships for atmospheric mercury and thereby promoting the development of risk management strategies based on sound science.

The areas of interest include but are not limited to the following:

(1) The investigation of natural sources of mercury and sources of recycled anthropogenic mercury emitted to air to better understand the relative importance of each and to provide additional data for atmospheric mercury modeling.

(2) The investigation of anthropogenic sources of mercury to air to better quantify both the rate and the speciation of their emissions.

(3) The performance of theoretical and laboratory investigations focused on understanding chemical and physical reactions of mercury with other constituents of the atmosphere.

(4) The development and evaluation of numerical simulation models of the emission, transport, transformation, and deposition of atmospheric mercury in order to identify the sources of mercury depositing to sensitive terrestrial and aquatic systems.

Proposed research should address the critical questions highlighted below:
(1) What fraction of the atmospheric mercury depositing to sensitive ecosystems in the U.S. is emitted from anthropogenic sources within the United States?  Within North America?

(2) What sources and/or source categories are most responsible for the atmospheric mercury depositing to sensitive ecosystems?

(3) What decrease in atmospheric mercury deposition can be expected from emission controls on various segments of domestic industry?  Worldwide industry?

(4) Over what period of time will these decreases in deposition occur?  Will the global cycling of anthropogenic mercury through land, water, biota, and air continue to augment natural mercury cycling for years, decades, or centuries?

Note: Proposals that only address or are solely limited in scope to just monitoring will not be considered responsive to the RFA.


Subject to the availability of funds, up to $6 million is expected to be awarded in fiscal year 2002 in this program area (total of $6 million over 3 years).  The projected award range is $200,000 to $300,000 per year total costs for up to 3 years.


Academic and not-for-profit institutions located in the U.S., and state or local governments, are eligible under all existing authorizations.  Profit-making firms are not eligible to receive grants from EPA under this program.  Federal agencies and national laboratories funded by federal agencies (Federally-funded Research and Development Centers, FFRDCs) may not apply.

Federal employees are not eligible to serve in a principal leadership role on a grant.  FFRDC employees may cooperate or collaborate with eligible applicants within the limits imposed by applicable legislation and regulations.  They may participate in planning, conducting, and analyzing the research directed by the principal investigator, but may not direct projects on behalf of the applicant organization or principal investigator.  The principal investigator's institution may provide funds through its grant from EPA to a FFRDC for research personnel, supplies, equipment, and other expenses directly related to the research.  However, salaries for permanent FFRDC employees may not be provided through this mechanism.

Federal employees may not receive salaries or in other ways augment their agency's appropriations through grants made by this program.  However, federal employees may interact with grantees so long as their involvement is not essential to achieving the basic goals of the grant.1  The principal investigator’s institution may also enter into an agreement with a federal agency to purchase or utilize unique supplies or services unavailable in the private sector.  Examples are purchase of satellite data, census data tapes, chemical reference standards, analyses, or use of instrumentation or other facilities not available elsewhere, etc.  A written justification for federal involvement must be included in the application, along with an assurance from the federal agency involved which commits it to supply the specified service.

 1 EPA encourages interaction between its own laboratory scientists and grant principal investigators for the purpose of exchanging information in research areas of common interest that may add value to their respective research activities.  However, this interaction must be incidental to achieving the goals of the research under a grant.  Interaction that is “incidental” is not reflected in a research proposal and involves no resource commitments.

Potential applicants who are uncertain of their eligibility should contact Jack Puzak  in NCER, phone (202) 564-6825, Email: puzak.jack@epa.gov.

Standard Instructions for Submitting an Application

A set of special instructions on how applicants should apply for an NCER grant is found on the NCER web site, https://www.epa.gov/ncer/rfa/forms/, Standard Instructions for Submitting a STAR Application.  The necessary forms for submitting an application will be found on this web site.

Sorting Codes

The need for a sorting code to be used in the application and for mailing is described in the Standard Instructions for Submitting a STAR Application.  The sorting code for applications submitted in response to this solicitation is


The deadline for receipt of the application by NCER is no later than 4:00 p.m. ET, August 15, 2001.


Further information, if needed, may be obtained from the EPA official indicated below. E-mail inquiries are preferred.

 William Stelz   202-564-6834