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STANDARDIZED AUTOMATED AND MANUAL METHODS TO SPECIATE MERCURY: FIELD AND LABORATORY STUDIES
Citation:
Landis, M S., R. K. STEVENS, E. Prestbo, AND F. A. Schaedlich. STANDARDIZED AUTOMATED AND MANUAL METHODS TO SPECIATE MERCURY: FIELD AND LABORATORY STUDIES. Presented at 223rd American Chemical Society National Meeting, Orlando, FL, April 7-11, 2002.
Impact/Purpose:
The overall research objective of this task is to improve our understanding of the emission, transport, transformation, and deposition of atmospheric mercury. Information garnered from this research is used to improve and evaluate EPA deterministic models that are used to investigate the (i) relative impact to local, regional, and global sources to atmospheric mercury deposition, and (ii) benefits of various emission reduction scenarios.
Specifically, individual research project objectives are listed below:
(1) Evaluate the ability of speciated mercury (Hg0, Hg2+, HgP) measurements to aid source apportionment models in identifying anthropogenic source contributions to atmospheric mercury deposition
(2) Elucidate the contribution of coal combustion sources to observed mercury wet deposition in the Ohio River Valley
(3) Obtain atmospheric profiles (200 - 12,000 ft) of speciated ambient mercury off the south Florida Coast
- Evaluate the role of long range transport of RGM to Florida in the marine free troposphere.
- Identify any vertical mercury gradients that might indicate the presence of rapid mercury chemistry in air or in cloud water.
(4) Conduct research at Mauna Loa Observatory to elucidate elemental mercury oxidation in the remote marine free troposphere.
(5) Conduct laboratory kinetics experiments to determine the rate constants of elemental mercury oxidation to gaseous inorganic divalent mercury species from atmospheric halide species (e.g. BrO, ClO).
Description:
The urban atmosphere contains a large number of air pollutants including mercury. Atmospheric mercury is predominantly present in the elemental form (Hg0). However emissions from industrial activities (e.g. incinerators, fossil fuel combustion sources and others) emit other forms of mercury some that are attached to particles and others that are in the vapor phase. Some of these vapor phase species (e.g. HgCl2) are highly water-soluble. Those Hg species that are water-soluble are called Reactive Gaseous Mercury (RGM). Particulate phase mercury (HgP) and RGM have much shorter half-lives in the atmosphere than Hg0 due to their higher removal rates through dry and wet deposition mechanisms and the low reactivity of Hg0. For this reason, sensitive areas near sources that emit RGM are likely to become contaminated.
Over the past 4 years, many scientists throughout the world, engaged in atmospheric mercury research have been using the newly developed KCl-coated quartz annular denuders to collect and measure RGM. Tekran Inc. manufactures automated instrumentation that incorporates this annular denuder. Recently a manual method to measure RGM and HgP has been developed jointly by the USEPA and the FL DEP. The method uses a uniquely designed manually operated KCL quartz denuders followed by a filter pack with a quartz filter to collect RGM and HgP, respectively. After collection, the denuders are thermally desorbed and the RGM converted to Hg0 and measured with a Tekran 2537A CVAFS analyzer, under laboratory conditions. As part of this research, the authors have observed that methods to measure HgP had a significant positive artifact when RGM coexists with HgP. This artifact was eliminated if a KCl coated annular denuder preceded the filter. The authors report for the first time quantitative data documenting the extent of this HgP sampling artifact. As part of this presentation, manual and automated measurements of RGM and HgP from a variety of field studies will be presented. The data to be presented document via statistical analysis the quantifiable ranges of uncertainties for the measurement of Hg0, RGM and HgP obtained with the automated and manual instrumentation.
This work has been funded wholly or in part by the United States Environmental Protection Agency Office of Research and Development. It has been subjected to peer review and approved for publication.