Mercury dry deposition
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Mercury Dry Deposition. EPA Local-Scale Air Toxics Ambient Monitoring Program Grant University of Nevada Reno – UNR Dr. Mae Gustin, Seth Lyman Frontier Geosciences Dr. Eric Prestbo Nevada Division of Environmental Protection. Grant Program Elements.

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Mercury Dry Deposition

  • EPA Local-Scale Air Toxics Ambient Monitoring Program Grant

    • University of Nevada Reno – UNR

      • Dr. Mae Gustin, Seth Lyman

    • Frontier Geosciences

      • Dr. Eric Prestbo

    • Nevada Division of Environmental Protection

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Grant Program Elements

  • “Development of broadly-deployable methods for quantifying atmospheric Hg speciation in urban and rural settings in Nevada”

  • Two-year Project

    • Awarded October 2005

    • Funding rec’d & project started June 2006

    • End date to be adjusted to June 2008

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Grant Program Elements

  • Co-location of project field sites with urban & rural MDN sites

    • Compare concentration & speciation of Hg at urban vs. rural locations

    • Better understanding of dry vs. wet deposition

    • Compare data collected upwind & downwind of naturally enriched areas & potential anthropogenic sources

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Grant Program Elements

  • Funding

    • $363,890 EPA Grant through NDEP

      • UNR, National Atmospheric Deposition Network & Frontier Geosciences

    • $582,576 Total Project Cost w/ Cost Shares

      • NDEP Equipment (incl. SO2 & O3 analyzers), FTE support and grant management

      • UNR & Frontier Geosciences - cost sharing

      • EPA continued support of MDN sites

      • Lesperance & Gibbs landowner participation

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(e.g. HgCl2, Hg(OH)2)

  • Emission & Re-Emission

  • Natural:

  • Soils & Hg enriched

  • areas

  • Plants

  • Geothermally Active

  • Zones

  • Anthropogenic:

  • Coal fired power plants

  • Waste incineration and other combustion

  • Mining activity

  • Chlor-alkali plants and other chemical production facilities

Overview of the Mercury Cycle

  • Atmospheric Conversion –

  • Sunlight and oxidants (ozone, hydroxyl radical) convert Hg(0) to RGM

  • RGM and Hg(0) sorb to particles and become Hg(p)

  • Complex chemistry

  • Relative amounts*:

  • Hg(0) – 90 to 99%

  • RGM – 0 to 10%

  • Hg(p) – 1 to 5%

  • (*Estimates based on Reno data)

Seth Lyman, UNR

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Overview of the Mercury Cycle






Wet Deposition

Re-emission of deposited mercury

(includes re-emission of both anthropogenic and naturally deposited mercury)

  • Dry Deposition –

  • Not well understood – little data exists

  • Site-specific

  • Projected atmospheric lifetimes:

  • RGM < Hg(p) < Hg(0)

Seth Lyman, UNR

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Project Building Blocks

  • Current UNR Project Nearing Completion re Dry Deposition

  • Mae Gustin, Seth Lyman, Frontier Geosciences, Oak Ridge Nat’l Lab, DRI, ranch landowners & EPA R9

  • Preliminary data on Hg speciation in air to develop insight re dry deposition of Hg in Reno & two rural MDN sites

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Project Building Blocks

  • Development & testing of field protocols for field use of ion exchange membranes

  • Interim project outcomes helped focus lab & field studies and reduce start-up time for new Air Toxics Grant

  • Collaborations in place with Ranchers, labs and others streamlined new grant

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Project Building Blocks

  • Project Goal: Measure atmospheric mercury species and try different techniques to infer dry deposition at the two Nevada MDN sites. UNR inferred dry deposition by:

    • Deploying Surrogate Surfaces

    • Measuring Soil Flux

    • Deposition on Leaf Surfaces

    • Applied Mathematical Models to measurements of RGM & Hg(p)

    • Compared all collected data and Wet Deposition (MDN) Data

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Project Building Blocks

  • Deploying Surrogate Surfaces

    • Exposed membrane faces oriented up, down, and vertically

    • 6-day deployment time

    • Trace-clean protocols utilized

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Mercury soil flux: Measures air-soil Hg(0) exchange – deposition and emission

Tekran 2537A, a 1L chamber, and a switching unit

Project Building Blocks

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Lesperance Ranch

Gibbs Ranch


Nevada MDN & Study Sites

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Expected Results

  • Dry deposition rates depend on meteorological and surface parameters, as well as the composition of mercury species in the atmosphere.

  • Each of the methods used showed that dry deposition was a significant component of total atmospheric deposition.

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Expected Results

  • The different methods showed similar seasonal and geographical variations in the depositional behavior of Hg(0), RGM, and Hg(p), and each form of Hg was found to be a significant and even dominant component of total dry deposition at some sites and/or seasons.

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Expected Results

Figure Deleted pending paper publication – for more information contact Jennifer Carr [email protected]

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Results to Apply to New Grant

  • Understanding of expected concentrations of different Hg species

  • Understanding of necessary detection limits for ambient samplers & field deployment time periods

    • (use 7 days = time between MDN samples?)

  • Understanding of QA/QC needed to obtain quality field data from passive samplers

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Need for Air Tox Grant

  • RGM is the most reactive of atmospheric mercury species, has shortest atmospheric residence time & is thought to have the highest deposition velocity

  • Little is known about dry depositional behavior of both RGM and Hg(0), only limited measures of deposition available

  • Tekran equipment is expensive & extensive training is required to operate

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Grant Program Elements

  • Currently setting up the new Reno MDN site, Ozone & SO2 monitoring equipment

  • UNR is developing a diffusive sampler for RGM with lab testing.

  • Frontier Geosciences is developing a total mercury diffusive sampler for UNR lab testing.

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Grant Program Elements

  • RGM diffusive samplers will be similar to the dry deposition sampler seen earlier

    • Similar in that the collection surface is a filter that has high affinity for RGM and not elemental mercury

    • Different in that the diffusive sampler collection surface is protected from atmospheric turbulence and, thus, collection to the filter is should be linear relative to RGM air concentration

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Barriers to turbulence

Diffusive region

Collection surface

Grant Program Elements

  • Nearing final development of an appropriate membrane for diffusive sampling to measure RGM concentrations utilizing apparent affinity for RGM

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Grant Program Elements

  • Diffusive sampler measures concentration, not deposition

    • For RGM, atmospheric concentration is the most important predictor of depositional flux

    • Concentration can then be used for calculations related to deposition

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Grant Program Elements

  • After lab testing is complete & units are ready, field testing will occur simultaneously with:

    • Tekran 2537A Gaseous Mercury Analyzer with 1130 (RGM) & 1135 (Hg(p)) speciation unit

    • micro-met and other routine ambient air quality parameters

  • Some testing will also be done by Frontier Geosciences in Seattle, WA to compare effects of climate on sampling system

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Grant Program Elements

  • After initial field testing is complete, proposal includes broad deployment at:

    • MDN sites (3),

    • a National Park Service AQ monitoring site,

    • transects down wind of a coal-fired power plant,

    • transects down wind of an ore-processing facility, and

    • transects down wind of a naturally enriched (geogenic) area

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Grant Program Elements

  • This final phase of field deployment will test ability to obtain measurement of RGM on broad scale, in remote locations with minimal training (NDEP as guinea pigs)

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Project Outcome Goals

  • To collect data to advance the understanding of major research questions related to biogeochemical cycle of Hg:

    • Can we do source apportionment by measuring atmospheric speciation using passive sampling systems?

    • How does Hg speciation in urban air compare with that of air at remote sites and those downwind of known anthropogenic sources?

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Project Outcome Goals

  • Cont’d:

    • How significant is dry deposition of Hg relative to wet deposition, especially in arid systems?

    • Since the dominant form of Hg in the atmosphere is Hg(0), is the dry deposition of Hg(0) more significant than RGM or Hg(p)?

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Ultimate Project Goals

  • Develop a system for measurement of Total Atmospheric Hg & RGM that:

    • Can be deployed reliably without high levels of technical training to be done with a simple instructional protocol that is easy to follow

    • Can be low in cost

    • Can be applied nationally