Grantee Research Project Results
2005 Progress Report: Inflow, Chemistry and Deposition of Mercury to the West Coast of the United States
EPA Grant Number: R829797Title: Inflow, Chemistry and Deposition of Mercury to the West Coast of the United States
Investigators: Jaffe, Daniel , Prestbo, Eric
Institution: University of Washington
EPA Project Officer: Chung, Serena
Project Period: June 1, 2002 through June 1, 2005
Project Period Covered by this Report: June 1, 2004 through June 1, 2005
Project Amount: $756,774
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 primary objectives of this research project are to: (1) quantify the flux of mercury (Hg) to the United States from global sources, (2) characterize the seasonal patterns and chemical speciation of this flux, and (3) examine the background deposition of mercury along the west coast of the United States. In particular we want to evaluate the significance of large mercury sources in Asia on transport and deposition of mercury in the United States. From our previous work, we know that long-range transport of pollutants from Asia to the United States occurs on a fairly regular basis.
Progress Summary:
Summary of key accomplishments: (1) obtainment of speciated Hg measurements at Mt. Bachelor; (2) identification of high reactive gaseous mercury (RGM) episodes in the free troposphere; (3) successful installation of Tekran 2537 on our aircraft and successful test flight; (4) analysis of previous data and comparison with the Goddard Earth Observing System (GEOS)-Chem global chemical transport model; and (5) development of an HgCl2 calibration system.
During the past year we continued our measurements of elemental Hg at Mt. Bachelor, a high elevation (9000’), free tropospheric site in central Oregon (March 2004-present). We also added in measurements of speciated mercury at this site. RGM is measured with a Tekran 1130 and particulate mercury (PHg) is measured with the Tekran 1135. We also installed a second Tekran instrument on our small aircraft and conducted one test flight. The results of this test flight were generally positive. We expect to conduct a full suite of science flights with the Tekran instrument onboard in the spring of 2006.
The Mt. Bachelor RGM measurements have given us some very interesting data. Although the RGM concentrations are usually low, in dry, subsiding air masses the concentrations can reach quite high levels. PHg levels were nearly always low. The high RGM periods were also associated with low Hg(0). This suggests conversion of Hg(0) to RGM, which is a key process in the global cycling of mercury. Figure 1 shows the data for the spring and summer of 2005.
Figure 1. Observations of Hg(0) (right scale), RGM and PHg (right scale) at Mt. Bachelor in 2005
Figure 2 shows the relationship between RGM and Hg(0) during these periods.
Figure 2. Change in RGM vs. Change in Hg(0) or GEM During Periods With Elevated RGM
The relationship is nearly 1:1. This again suggests conversion of Hg(0) to RGM, with relatively little loss, which is consistent with no rainout in a subsiding air mass.
Because this is a key process in the global mercury cycle, all global models must include this oxidation process; however, there are significant uncertainties associated with the oxidants, oxidation rates, products, and removal of the RGM. Through collaboration with the Goddard Earth Observing System-Chem modeling group (at Harvard University and University of Washington), we have compared our Mt. Bachelor Observatory (MBO) data to their state of the art global mercury model. The results are shown in Figure 3.
Figure 3. Comparison of the GEOS-Chem Modeled RGM With Observations From MBO for 2005
The model does a reasonable job of capturing the mean concentration and the diurnal cycle; however, it does not capture the high RGM peaks seen on some days. One of our key goals in 2006 is to identify the cause of these high RGM peaks and understand why the model does not capture them. This is a key task for understanding the global mercury cycle. These results are in a manuscript, which has been submitted to the Journal of Geophysical Research for publication.
Because of the importance of Hg speciation, it is important that the measurements are accurate and that any biases or artifacts caused by changing atmospheric conditions or analytical procedures are identified. Although a few intercomparison campaigns and quality assurance measurements have been made there has been no robust field calibration technique for RGM. Without such a system, the current atmospheric mercury speciation method remains operationally defined. To remedy this situation, work was begun at Frontier Geosciences to develop RGM spiking/calibration methods. One method involves spiking KCl coated denuders with known quantities of RGM in a liquid form (as HgCl2). Spiked denuders are shipped into the field, loaded, and desorbed into a speciation system, ensuring the system is making accurate RGM measurements. Denuders have been spiked at concentrations ranging from 24.2 pg to 96.9 pg, with 90.5 percent to 94.9 percent recoveries. Preliminary analysis on the effects from denuder temperature and holding time study show no appreciable loss of RGM on denuders stored for 2 days at 21 degrees C. A second method involves injecting liquid based RGM standard onto a quartz cup suspended in the inlet of a sampler. Both cup and inlet are heated. Following injection, the liquid rapidly volatilizes leaving HgCl2 to vaporize into the denuder. This dynamic method best simulates conditions during normal sampling operation. Spikes ranging from 24.2 pg to 96.9 pg have been produced with recoveries of 78.1 percent to 88.0 percent. Delivery technique and proper heating of the inlet and quartz cup have proven critical towards reaching recoveries in this range. Frontier continues to develop this method and will hopefully develop a field-usable unit in the near future.
Future Activities:
The main activities to be pursued in the coming year include:
1. Continue our analysis of data obtained to date and continue the observations of speciated mercury at MBO.
2. Conduct aircraft vertical profiles of Hg(0). This will take place in the spring of 2006. In addition to Hg, the aircraft will also measure CO, O3, aerosols, and temperature/Rh. These observations will provide an important constraint to global models on the vertical distribution and lifetime of global atmospheric Hg.
3. Continue to collaborate with the GEOS-Chem group on its model of the global mercury cycle. This should lead to several additional publications.
Journal Articles on this Report : 4 Displayed | Download in RIS Format
| Other project views: | All 34 publications | 7 publications in selected types | All 7 journal articles |
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Jaffe D, Prestbo E, Swartzendruber P, Weiss-Penzias P, Kato S, Takami A, Hatakeyama S, Kajii Y. Export of atmospheric mercury from Asia. Atmospheric Environment 2005;39(17):3029-3038. |
R829797 (2004) R829797 (2005) R829797 (Final) |
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Keating T, West J, Jaffe D. Air quality impacts of intercontinental transport. EM: The Magazine for Environmental Managers, October 2005, pp. 28-30. |
R829797 (2005) R829797 (Final) |
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Swartzendruber P, Jaffe DA, Prestbo EM, Weiss-Penzias P, Selin NE, Park R, Jacob DJ, Strode s, Jaeglé L. Observations of reactive gaseous mercury in the free troposphere at the Mount Bachelor Observatory. Journal of Geophysical Research 2006;111:D24301, doi: 10.1029/2006JD007415. |
R829797 (2005) R829797 (Final) |
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Weiss-Penzias P, Jaffe DA, Swartzendruber P, Dennison JB, Chand D, Hafner W, Prestbo E. Observations of Asian air pollution in the free troposphere at Mount Bachelor Observatory during the spring of 2004. Journal of Geophysical Research 2006;111:D10304, doi:10.1029/2005JD006522. |
R829797 (2004) R829797 (2005) R829797 (Final) |
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Supplemental Keywords:
air, ambient air, tropospheric pollution, chemical transport, toxics, air toxics, metals, heavy metals, mercury, environmental chemistry, atmospheric chemistry, Pacific Northwest, EPA Region 10, long-range transport,, Scientific Discipline, Water, Mercury, Environmental Chemistry, Ecology and Ecosystems, West Coast, marine boundary layer, mercury detection, atmospheric deposition, mercury measurement, fate and transport, formation, chemical speciationRelevant Websites:
http://faculty.washington.edu/djaffe Exit
Progress 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.