1. 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

2. 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

3. 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

4. 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

5. Overview of the Mercury Cycle
Hg(p) •
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
Hg(0)
RGM
Hg(p)
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
(e.g. HgCl2, Hg(OH)2)
Relative amounts*:
Hg(0) – 90 to 99%
RGM – 0 to 10%
Hg(p) – 1 to 5%
(*Estimates based on Reno data)
Seth Lyman, UNR

6. Overview of the Mercury Cycle• • • • • • • •
Hg(p) • •
RGM
Hg(p)
Hg(0)
RGM
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

7. 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

8. 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

9. 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

10. Project Building Blocks
Deploying Surrogate Surfaces
Exposed membrane faces oriented up, down, and vertically
6-day deployment time
Trace-clean protocols utilized

11. Project Building Blocks
Mercury soil flux: Measures air-soil Hg(0) exchange – deposition and emission
Tekran 2537A, a 1L chamber, and a switching unit

12. Nevada MDN & Study Sites
Reno
Gibbs Ranch
Lesperance Ranch

13. Gibbs Ranch, North of Wells, NV

14. Lesperance Ranch near Paradise Valley, NV

15. 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.

16. 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.

17. Expected Results
Figure Deleted pending paper publication – for more information contact Jennifer Carr

18. 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

19. 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

20. 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.

21. 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

22. 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

23. 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

24. 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

25. 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

26. 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)

27. 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?

28. 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)?

29. 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