Grantee Research Project Results
2004 Progress Report: Speciated Atmospheric Mercury: Gas/Particle Partitioning, Transformations, and Source Characterization
EPA Grant Number: R829798Title: Speciated Atmospheric Mercury: Gas/Particle Partitioning, Transformations, and Source Characterization
Investigators: Schauer, James J. , Armstrong, D. E. , Krabbenhoft, David P. , Hurley, James P. , Gross, Deborah S.
Institution: University of Wisconsin - Madison , United States Geological Survey , Carleton College
Current Institution: University of Wisconsin - Madison , Carleton College , United States Geological Survey
EPA Project Officer: Chung, Serena
Project Period: January 1, 2003 through December 31, 2005 (Extended to December 31, 2006)
Project Period Covered by this Report: January 1, 2004 through December 31, 2005
Project Amount: $898,388
RFA: Mercury: Transport, Transportation, and Fate in the Atmosphere (2001) RFA Text | Recipients Lists
Research Category: Heavy Metal Contamination of Soil/Water , Air Quality and Air Toxics , Air , Safer Chemicals
Objective:
The overall objective of this research project is to understand the relationships of atmospheric mercury (Hg) and other atmospheric components. This holistic approach to assessing atmospheric Hg will provide a better understanding of the sources of speciated atmospheric Hg, as well as the key atmospheric processes that impact the fate of Hg in transport from sources to receptor sites.
The project is comprised of three major thrusts that are integrated to achieve the overall project objective:
- Simultaneously quantify and speciate the chemical forms of atmospheric Hg and other atmospheric pollutants at near-source impacted regions and sensitive receptor sites. Chemical speciation will include elemental Hg (Hg0), reactive gaseous Hg, and particulate Hg (pHg).
- Quantification of atmospheric conditions and aerosol properties that control gas/particle partitioning of the chemical forms of Hg in the atmosphere.
- Identification and quantification of homogenous and heterogeneous atmospheric chemical reactions of Hg with an emphasis on processes involving processes involving aerosols, fog water, and cloud water.
Progress Summary:
In Year 1 of the project, a series of atmospheric Hg sampling campaigns were successfully completed at Devil’s Lake State Park, Wisconsin; Yellowstone National Park, Wyoming; and a highly industrialized region of East St. Louis, Illinois. In Year 2, there were two major field efforts. The first was colocation of a single particle mass spectrometer (aerosol time-of-flight mass spectrometer) with the Hg monitoring instruments at the East St. Louis site. The second field effort was the initiation of a year-long sampling campaign (June 2004-May 2005) examining atmospheric Hg speciation in Milwaukee, Wisconsin. As well, a considerable effort in Year 2 was directed towards the preparation of manuscripts for publication in peer-reviewed journals.
In parallel with the field campaigns, experimental laboratory-based capabilities established in Year 1 of the project were continued. These capabilities were focused in two key areas: (1)laboratory experiments and modeling efforts to study the potential formation and destruction of methylmercury (MeHg) in fog and cloud water, and (2) the development and subsequent use of an aerosol flight tube to study the gas to particle partitioning of reactive Hg as a function of aerosol composition.
Laboratory Studies
The composition of reactive Hg and MeHg complexes in cloud and fog waters were determined using a thermodynamic model for a range of chemical compositions representing several different regions of the United States and Europe. We determined that for typical atmospheric conditions there were limited potential chemical pathways available for MeHg formation in the atmosphere. Laboratory experiments also were conducted in Years 1 and 2 to examine the potential formation of MeHg in rain water and simulated cloud water. The results of these experiments indicate that MeHg is more likely destroyed in the atmosphere than formed in atmospheric waters, suggesting that the source of MeHg in atmospheric waters is not in situ production.
The atmospheric chemistry of reactive Hg still requires further study to improve current knowledge. In particular, little is known about the gas to particle partitioning of reactive Hg to dry aerosol particles. An aerosol flight tube has been developed over the course of this project to determine the gas to particle partitioning coefficients of reactive Hg for a variety of atmospherically relevant aerosol compositions. In Year 1, the aerosol flight tube was configured and evaluated to assure that Hg experiments could be done in the reactor at relevant Hg concentrations without significant Hg losses or contamination. These demonstrated to be adequate for the experiments preformed in Year 2 and proposed for Year 3. The system allows monodispersed aerosols, with well-defined compositions to be mixed with reactive Hg and/or Hg0 upstream of the flight tube. The flight tube allows sufficient residence time to allow gas/particle partition to reach equilibrium. Sampling systems were configured upstream and downstream of the flight tube to mass balance the Hg in the system.
Currently, there are a number of publications that are either submitted for review or in preparation for submission to peer-reviewed journals. Specifically, one manuscript describing the effort at Devil’s Lake currently is in review. Two manuscripts describing the East St. Louis effort currently are in preparation. One of these manuscripts describes the concentrations of reactive Hg and Hg0 observed at the site, and the corresponding metal data used to identify possible sources of Hg. The other is a study examining factors affecting gas/particle partitioning of pHg in East St. Louis. A fourth manuscript covering results of the measurements made in Yellowstone Park has been prepared. The aerosol flight tube studies are expected to provide a paper that describes and verifies the design and operation of aerosol flight tube and presents gas to particle partitioning coefficients of reactive Hg as a function of particle composition. The laboratory work examining MeHg formation in atmospheric water resulted in the completion of one Master of Science graduate degree, and this work will be published as two papers (one detailing the modeling effort and the other reporting on experiments designed to measure MeHg formation in rain and cloud water), which will be submitted to the peer-reviewed literature in Year 3.
Future Activities:
In Year 3 of the project, an additional 6 months of measurements will be made at the Milwaukee location to obtain a full 12-month time series of Hg and other atmospheric pollutant measurements in an urban area. At the completion of these measurements, the Tekran Hg analyzers will be moved to Riverside, California for a 3-week intensive sampling period during periods of photochemically induced smog. Both the Milwaukee and Riverside measurements will provide urban data sets that contrast the rural measurements made in Devil’s Lake, Mount Horeb, and Yellowstone National Park and will augment our East St. Louis data. All of our data are being used to identify local and regional sources and processes that are impacting atmospheric Hg species, and significant efforts in Year 3 will continue to address the analysis and interpretation of the field measurements made in Years 1 and 2. As well, laboratory studies in Year 3 will continue to assess the impact of aerosol composition of the gas/particle partitioning of divalent Hg species.
Journal Articles:
No journal articles submitted with this report: View all 8 publications for this projectSupplemental Keywords:
particulate matter, PM, St. Louis Midwest Supersite, reactive gaseous mercury, RGM, mercury, elemental mercury, aerosols, gas/particle partitioning, speciation, atmospheric chemistry, deposition, oxidation,, Air, Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, INTERNATIONAL COOPERATION, Waste, POLLUTANTS/TOXICS, Fate & Transport, Air Quality, Environmental Chemistry, Chemistry and Materials Science, air toxics, Chemicals, Environmental Monitoring, heavy metals, atmospheric chemistry, atmospheric mercury chemistry, atmospheric deposition, fate and transport, air pollutants, chemical kinetics, Hg, mercury chemistry, mercury cycling, contaminant transport models, mercury vapor, atmospheric mercury cycling, mercury emissions, modeling, atmospheric mercuryProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.