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Project Title: Development of Techniques to Directly Measure Mercury Dry Deposition
Synopsis: This project is intended to develop an inexpensive, easy to use and accurate method to directly measure the deposition of mercury to surfaces from the air. Currently, the most commonly used method for estimating this amount involves a complicated and expensive series of measurements of mercury in air and the use of models and calculations to relate these air concentrations to the amount of mercury reaching the surface. This method is both expensive and difficult for conduct for all but those with the highest level of expertise in taking these measurements. While some other measurement methods have been attempted, work is still required to ensure these methods are accurate and standardized and to make them more widely accessible to public agencies and others who may desire to take such measurements.
This project will develop and test a mercury dry deposition measurement technique involving the use of exposed filters with various coatings. These filters are exposed to the open air by being secured to the top of a horizontal service for a given period of time. They are then analyzed in a laboratory to determine the amount of mercury that has accumulated on them. By using various coatings on the filters, the deposition of different types of mercury can be assessed. The intent is to provide an inexpensive method that results in accurate measures of mercury dry deposition over a moderately long timeframe (for example, several days to two weeks). Such a technique could be used in tandem with commonly used wet deposition measurements (such as rain collection) to determine the total amount of mercury reaching a given surface from the air. Such information is essential in determining the behavior of mercury in the Great Lakes and other water bodies and is currently not widely known for most locations.
Chemicals Studied: The study will focus on mercury, a substance of high concern
within the Great Lakes region due to its high toxicity and tendency to accumulate
at high levels within fish. The study will examine concentrations of elemental
and reactive (Hg(0) and Hg(II)) mercury in the gaseous and particulate dry
deposition from the atmosphere.
Methods Used: The anticipated design consists of a round, horizontal disc
to control air flow over the surface of the sampler filter, which will be bracketed
to the surface of the disc. A combination of gold-coated, Teflon-coated and
KCl-coated filters will be used to take advantage of their varying abilities
to retain particulate, reactive gaseous and elemental gaseous mercury. Once
the sampling period is concluded, the filters will be retrieved. They can be
analyzed in the same manner as filters used to obtain particulate air samples.
A sampler housing will be adapted to provide coverage to the sampler during
periods of rain.
Potential Results and Implications: The method to be developed here will be immensely useful for those looking to obtain measures of mercury dry deposition but who lack the funds or expertise to use methods based on measurements of multiple mercury species in air. Depending on the reason for the sampling, this method, which will provide an average measure over an extended timeframe, may prove to be a useful replacement even for those with the funds and expertise for other methods. Widespread adaptation of a simple and inexpensive technology for measuring mercury dry deposition could help fill one of the greatest uncertainties regarding how much mercury is reaching water bodies from the atmosphere. Currently, most such assessments are made based on measurements of mercury in rain and assumptions or guesses as to how much deposits from the air during dry conditions. Filling this gap will give scientists and policy makers much better certainty in determining what means may be available for better controlling mercury in the environment.