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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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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

Hg(0)RGM Hg(p)

Emission & Re-EmissionNatural:• 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

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

Hg(p)•••••

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Overview of the Mercury Cycle

RGM

Hg(p)•••••

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Hg(0)RGM Hg(p)

Dry Deposition –• Not well understood – little data exists• Site-specific• Projected atmospheric lifetimes: RGM < Hg(p) < Hg(0)

Wet Deposition

Re-emission of deposited mercury(includes re-emission of both anthropogenic and naturally deposited mercury) 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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Project Building Blocks

• Mercury soil flux: Measures air-soil Hg(0) exchange – deposition and emission Tekran 2537A, a 1L

chamber, and a switching unit

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Nevada MDN & Study Sites

Reno

Gibbs Ranch Lesperance Ranch

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Gibbs Ranch, North of Wells, NV

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Lesperance Ranch near Paradise Valley, NV

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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 jcarr@ndep.nv.gov

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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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Grant Program Elements

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

Barriers to turbulence

Diffusive region

Collection surface

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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