Grantee Research Project Results
2003 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, 2003 through December 31, 2004
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 , Safer Chemicals , Air
Objective:
The overall objective of this research project is to understand the relationships of atmospheric mercury and other atmospheric components. This holistic approach to assessing atmospheric mercury will provide a better understanding of the sources of speciated atmospheric mercury (Hg), as well as the key atmospheric processes that impact the fate of mercury 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, reactive, and particulate Hg.
- 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 field sampling campaigns were successfully implemented including: (1) the completion of 9 months of continuous atmospheric mercury monitoring at Devil’s Lake State Park; (2) a 2- week intensive atmospheric mercury monitoring effort in Yellowstone Park; and (3) two separate month-long atmospheric mercury monitoring efforts at a highly industrialized region of East St. Louis, Illinois.
Devil’s Lake State Park is in a relatively remote region of central Wisconsin. During the 7-month sampling effort, the plume from a large power plant in Portage was measured at Devil’s Lake about a dozen times. The subject power plant is located about 30 miles from the sampling site. The plume from the power plant had a significant impact on reactive gaseous mercury (RGM) concentrations at the site but little impact on the total mercury concentrations. Gaussian plume modeling efforts currently are underway to assess the implications of these measurements on the speciation of mercury in the emissions from this source.
During a 2-week period of the Devil’s Lake monitoring efforts, parallel mercury measurements were simultaneously made about 30 miles south in Mt. Horeb, Wisconsin. Very strong correlations were observed in the concentrations of elemental mercury at these two sites supporting the regional nature of elemental mercury. In contrast, very little correlation in RGM concentrations was observed among these two rural sites, which suggests that RGM concentrations at these sites were controlled by localized sources and not regional processes. Particulate mercury was found to have moderate correlation suggesting that particulate mercury concentrations at these sites are impacted by both regional and local sources.
The measurements made in Yellowstone National Park showed surprisingly low concentrations of all mercury forms. Although mercury concentrations in the park were clearly above global background levels, the concentrations in the park were much lower than would be expected in Yellowstone National Park was a major source of atmospheric mercury. Although data analysis is still in progress, a preliminary analysis of the data suggests that the dominate source of atmospheric mercury in Yellowstone Park during the sampling event was forest fires outside of the park. This result if somewhat surprising due to the fact that several of the lakes in Yellowstone Park have extremely high mercury concentrations that are believed to arise from geothermal inputs.
Measurements in East S. Louis were made at the U.S. Environmental Protection Agency-funded St. Louis Midwest Supersite. The site was selected because a wide range of advanced aerosol chemical characterization instruments were operating at this site and it is an urbanized area that is heavily impacted by emissions from local industries. Although the background levels of atmospheric elemental mercury in East St. Louis were similar to levels reported in many rural locations, extremely high concentrations of all forms of mercury were frequently observed at the site, which result from the impact of plumes from local sources. Peak concentrations of elemental mercury exceeded 300 ng m-3, and peak concentrations of RGM exceeded 30,000 pg m-3. These concentrations represent levels significantly higher than previously reported in urban areas and are indicated of major mercury emissions sources. The mercury measurements along with measurements of airborne pollutants are being used to identify the plumes and develop mercury speciation profiles for the specific plumes. In addition, the non-plume-impacted mercury concentrations are being used to assess what aerosols properties are impacting the gas/particle partitioning of divalent mercury. Preliminary results suggest that aerosol nitrate ion plays a role in mercury gas/particle partitioning. Because of the richness of the data obtained in East St. Louis, a second field monitoring effort is being implemented in East St. Louis that spans the winter of 2003-2004 (Project Years 1 and 2). The second deployment includes the project teams aerosol time-of-flight mass spectrometer (ATOFMS), which provides real-time information of the composition of individual aerosol particles. The ATOFMS measurements are ideal for identifying plumes and the composition of aerosols that impact the partitioning of divalent mercury. It is important to recognize that ATOFMS data are very rich and complex. Data analysis for this effort is being enhanced by the University of Wisconsin (UW)-Madison National Science Foundation-funded Information Technology Research (ITR) project that is a collaboration between the computer science departments and the environmental chemistry departments at UW-Madison and Carleton College.
In parallel with the field campaigns, experimental laboratory based capabilities were established in Year 1 of the project. These capabilities were focused in two key areas: (1) the development of an aerosol flight tube to study the interaction of well-defined laboratory aerosols and divalent forms of mercury; and (2) laboratory methods to study the potential formation and destruction of methyl mercury in fog and cloud water.
In Year 1, the aerosol flight tube was configured and evaluated to assure that mercury experiments could be done in the reactor at relevant mercury concentrations without significant mercury losses or contamination. These demonstrated to be adequate for the proposed experiments. The systems allows monodispersed aerosols with well defined compositions to be missed with reactive mercury and/or elemental mercury upstream of the flight tube The flight tube allows sufficient residence time to allow gas/particle partition to reach equilibrium. Sample systems have been configured upstream and downstream of the flight tube to mass balance the mercury in the system. Year 2 will be used to further test the system and commence experiments to assess the role of aerosols size and composition on divalent mercury gas/particle partitioning.
Future Activities:
In Year 2 of the project, an additional 5 months of measurements will be made at Devil’s Lake to obtain a full 12-month time series of mercury and other atmospheric pollutant measurements. At the completion of these measurements, parallel 12-months of measurements will be made in Milwaukee, Wisconsin. The Milwaukee measurements will provide an urban data set that contrasts the rural measurements made in Devil’s Lake. Both sets of measurements are being used to identify local and regional sources and processes that are impacting atmospheric mercury species. In addition, measurements in East St. Louis will continue into Year 2 to obtain a 3-month time series of atmospheric mercury measurements that are collected in parallel to a wide range of aerosol measurements including single particle ATOFMS measurements. Significant efforts in Year 2 will address the analysis and interpretation of the field measurements made in Years 1 and 2.
Laboratory studies in Year 2 will be focused on assessing the impact of aerosol composition of the gas/particle partitioning of divalent mercury species, as well as the fate and potential formation of methyl mercury in rain water, fog water, and aqueous extracts of atmospheric aerosols. The partitioning experiments will examine the impact of major atmospheric aerosol constituents on gas/particle partitioning of mercury. The atmospheric aqueous chemistry experiments will incorporate real fog water, rain water, and atmospheric aerosols extracts as well as artificial solutions that cover the range of fog and cloud waters reported in the literature.
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, mercury, elemental mercury, aerosols, gas/particle partitioning, speciation, atmospheric chemistry, deposition, oxidation,, Scientific Discipline, Air, INTERNATIONAL COOPERATION, Waste, Ecosystem Protection/Environmental Exposure & Risk, POLLUTANTS/TOXICS, Air Quality, air toxics, Environmental Chemistry, Chemicals, Fate & Transport, Environmental Monitoring, Chemistry and Materials Science, fate and transport, air pollutants, Hg, mercury, mercury emissions, modeling, mercury cycling, chemical kinetics, atmospheric mercury chemistry, mercury chemistry, atmospheric chemistry, atmospheric mercury cycling, atmospheric deposition, contaminant transport models, heavy metals, mercury vaporProgress 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.