Regional Atmospheric Mercury Study CompletedThe UMAQL had two primary objectives for GLAMAP:
(1) to establish a regional monitoring program for investigating the transport of and determining the source areas for atmospheric mercury in the Great Lakes region, and
(2) to facilitate cooperation among Great Lakes agencies and research groups to maintain this monitoring program.
Installation of the sampling equipment at themonitoring sites began in November 1994 with the lastsite operational in May 1995. Sample collection for the GLAMAP monitoring network was completed in December 1996, providing 19 to 24 months of atmospheric mercury measurements for each site.
The methods used for collection and analysis of total particle- and gas-phase mercury samples have been submitted for publication in a US-EPA document entitled "Compendium of Methods for the Determination of Inorganic Compounds in Ambient Air" which is due to be published in 1998.
Measurements of total particulate matter were also obtained on the same sampling schedule for determination of partriculate trace elements. Patriculate samples were collected by using Teflon filters and analyzed by x-ray fluorescence at the US EPA-NERL for a number of elements.
In addition, the efforts of the network site operators were instrumental in creating a high qualitydatabase for atmospheric mercury in the Great Lakes region: Darrel Smith, Mark and Nancy Witty, Beth LaValley, Dennis Sotala, Shuli Rayberg, Kelly Monahan, Christine Messinger, Mike Snider, Kathy Felt, Karen Teed, Bill Colon, David Bosanko.
Great Lakes Data Base for Atmospheric Mercury AnalyzedThe measurements of atmospheric mercury andtrace elements from the GLAMAP monitoring network generated a significant amount of data over the two years of the study. A total of more than 1,100 sets of 24-hour measurements were collected for gas- and particle-phase mercury from all ten of the network sites from December 1994 to December 1996.
analysis and interpretation of this large data base provided the first spatially resolved assessment of atmospheric mercury levels for the entire Great Lakes region. Spatial and temporal trends in atmospheric mercury levels for the entire Great Lakes region. Spatial and temporal trends in atmospheric mercury concentrations were evaluated based on the two years of measurements. The influence of meteorolgoical factors on the observed spatial and temporal trends was also evaluated.
To investigate the transport of atmospheric mercury across the Great Lakes region, air mass trajectories were calculated for each sample at each site using the HY-SPLIT model (NOAA Technical Memorandum ERL ARL-195). These air mass trajectories will be combined with the measured levles of atmospheric mercury in a hybrid receptor model to quantitatively determine the impact of different source areas on atmospheric mercury levels within the Great Lakes region.
In addition, particulate trace element data will be used in source apportionment techniques to identify the types of sources influencing atmospheric mercury levels in the Great Lakes region.
Spatial and Temporal Trends Evident in Atmospheric Mercury Measurements for RegionSignificant spatial and temporal trends were evident in the levels of atmospheric mercury measured during GLAMAP. Gas-phase mercury concentration measured during the two-year study period ranged from 1.0 to 3.5 ng/m3, and particle-phase mercury concentrations ranged over two orders of magnitude (1-100 pg/m3). These levels of atmospheric mercury are typical of rural/remote areas within the continental U.S.
Average concentrations for each network site are displayed in Figures 2 and 3 for gas- and particle-phase mercury, respectively.Average gas-phase mercury concentrations differed by approximately 25% across the Great Lakes region (1.63-2.03 ng/m3) and average particle-phase mercury levels differed by nearly a factor of three (9-25 pg/m3).
Concentrations of both gas- and particle-phase mercury were higher at sites in the eastern and southern parts of the region compared to sites in the northern and western parts of the region. Statistical tests confirmed that significant differences in both gas- and particle-phase mercury levels were measured across the Great Lakes region during GLAMAP.
Temporal trends were also observed during GLAMAP, although the trends were different for the two atmospheric mercury species. For gas-phase mercury, the sample-to-sample variability was greater at sites with higher average concentrations (eastern and southern sites). The opposited was observed for particle-phase mercury, where sample-to-sample variability was greater at sites with lower average concentrations (northern and western sites).
These temporal trends incdicate that GLAMAP sites with higher average gas-phase mercury concentrations had individual samples with elevated concentrations, while sites with higher average particle-phase mercury concentrations had consistently elevated concentrations.
Atmospheric mercury concentrations for the two sampling years were not statistically different for both gas- and particle-hase mercury.However, seasonal differences were statistically significant for GLAMAP sites.
For gas-phase mercury, seasonally averaged concentrations were highest for the spring season. This seasonaltrend appeared to be influenced by regional-scale or larger processes, since the trend was consistent across most of the GLAMAP sites and both sampling years.
For particle-phase mercury, concentrations were consistently higher in the winter months at sites in the eastern and southern parts of the region, but not across all of thenetwork sites. Therefore, different influences wre important in the seasonal variations of these two atmospheric mercury species.
The results from x-ray fluorescence (XRF) analysis of the GLAMAP particulate samples produced a unique database of element concentrations for the Great Lakes region. Elements quantified by the XRF technique for these GLAMAP sites included crustal elements and elements typical of anthropogenic (man-made) emissions, as well as elements which can be from either crustal or anthropogenic sources.
Average concentrations for these groups of elements had different spatial trends for the Great Lakes Region. Average concentrations of all the crustalelements were higher at sites inteh southern and western parts of the Great Lakes region, with a decreasing trend toward the northeast. Average concentrations of the other elements typically emitted from anthropotenic sources indicate a spatial pattern similar to that observed for atmospheric mercury. The GLAMAP sites located in the eastern and southern parts of the Great Lakes region had higher aveage concentations of the anthropogenic elements compated to the sites in the northern and western parts of the region.
These elemental concentrations will be utilized in source-apportionment techniques to identify the types of sources contributing to atmospheric mercury levels in the Great Lakes region.
Send comments or requests for copies of the newsletter to:
Gerald Keeler, Director
Univ. of Michigan Air Quality Lab.
Dept. of Environ. and Ind. Health
School of Public Health
109 S. Observatory Street
Ann Arbor, Michigan 48109-2029
e-mail: jkeeler@umich.edu
Editor: Janet Burke
Production Coordinator: Renita M. Bellmore
