The pilot network for passive gaseous mercury monitoring is set to begin sampling on December 31, 2024. The primary objective of this initiative is to establish a new monitoring network that will complement existing networks such as Mercury Deposition Network (MDN), Atmospheric Mercury Network (AMNet), and Mercury Litterfall Network (MLN). This new network will measure quarterly average Gaseous Elemental Mercury (GEM) using a passive sampler, which can be easily deployed across the U.S. and internationally. It will serve as a foundational network for AMNet, a companion to the MDN, and has the potential to provide average dry deposition estimates for all participating sites.

This initiative directly supports the National Atmospheric Deposition Program (NADP) mission by providing scientifically accurate measurements of gaseous mercury, which can be used to estimate dry deposition. It builds on the goals of AMNet by expanding the network with additional sites and stations, thereby strengthening NADP’s overall efforts. The methods proposed have been rigorously reviewed and approved through scientific channels, are immediately available, and will help foster further research and dialogue. Furthermore, the initiative addresses a global need, making it a key step in advancing NADP’s mission and objectives.

Passive mercury measurements can be added to existing AMNet, MDN, or MLN site operations, or a new passive mercury site can be established.

There is minimal time required to perform the quarterly sample change once a site joins the passive mercury pilot network. During the quarterly sample changeout the operator will be asked to wear vinyl gloves (supplied by NADP) to minimize potential contamination of the passive sample. The operator will ship the passive sampler set (6 samplers in total) and the field form back to the NADP laboratory (NAL).

Upon receipt of the passive samples at the Wisconsin State Laboratory of Hygiene (WSLH)/Trace Element Clean Lab (TECL), the sample analysis will be performed on the Nippon Model MA-3000 instrument. Analysis is through Direct Thermal Decomposition-Gold Amalgamation-CVAAS. Essentially, the mercury compounds are collected using elemental carbon, and the carbon is combusted in the MA-3000. Mercury is volatilized as elemental Hg and collected by the instrument’s gold traps. Analysis is by Cold Vapor Atomic Fluorescence (the same method as the MDN and AMNet).

The current cost for adding a passive mercury site is $4,000 per year (which includes the samplers, analyses, QA, and return shipping). During the pilot network (2025) the NADP Program Office (PO) and WSLH/TECL will work to identify further efficiencies and the costs for operating as a network will be re-evaluated.

CONTACT
David Gay, NADP Coordinator
Email: dgay2@wisc.edu
Tel. 608-263-9162

Operator support is available to help answer questions about sampling, shipping, and general site questions. Call the 1-800-952-7353 toll free number or send an email to nadp@slh.wisc.edu.

Standard Operating Procedures (SOPs)

Before the first deployment, the brackets will need to be installed in a location that allows for free-flowing air. Other mounting structures may be used as needed, as long as air flow is not obstructed. Screws are preferred for mounting the bracket. If cable ties are used for mounting, they should be carefully inspected for signs of weathering and replaced as needed.

• Passive Mercury Site Operator Instructions
• Passive Mercury Field Form
• Tekran MerPAS Instruction Sheet

Mounting Bracket Installation

The first shipment of materials will contain the following parts:

4 brackets (6” galvanized zinc)

12 screws (1” deck screws with Phillips head)

12 washers

8 cable ties (21” nylon)

The site operator may need to provide other tools (e.g., a drill) to complete the installation of the brackets.

Sampling Schedule

The sampling device is a passive measurement for GEM, developed by a research group at the University of Toronto with support from Environment and Climate Change Canada. The device is also produced commercially by Tekran Instruments Corp, and sold as the “MerPAS” (see figure). The passive device is very similar to the Radiello sampling device used in the AMON.

The MerPAS device includes three major parts;

1. a polyethylene terephthalate (PET) jar shield,
2. a Radiello sample body/housing
3. a sample core.

Like most passive air samplers, the sample body is porous and allows gases to move from free air outside the body to the inside the body. It also provides a quiescent space for GEM to diffuse to the core over this space. The core material is housed in a metal mesh core container which is filled with a mixture of commercially available, bituminous coal-derived, sulfur-impregnated activated carbon. The GEM adsorbs to the AC inside the sampler body, and is stable over time. The Radiello core and body slip-fit together and include an endcap to make the sampling device. The device screws into the precipitation shield which keeps the device dry. A shield comes with a wall mount to attach to a wall, fencepost, etc. for sampling. The shield is closed with a PET jar lid for storage and transport to and from the sites.

Sampler Selection Justification

• The MerPAS has been well reviewed in the literature and this method has shown to be accurate in many different environments and at the atmospheric concentration levels that we need.
• The method is currently used in a small but global effort by several Canadian scientists and has been considered for addition to the APMMN networks. This suggests some global acceptance as a standard measurement that can be incorporated into national/global networks and for support of Minamata goals.
• MELD has gone through a thorough review of the MerPAS system, and per the report is a valid method now, that received a good bit of support by the MELD reviewers as a viable, inexpensive, and accurate measurement system.
• The MerPAS is a commercial product by Tekran Instruments, our current partner in AMNet. After discussions with Tekran, they are willing to help the network in a variety of ways, and particularly with initial startup and quality assurance

To establish a new network (or subnetwork), advocates complete a 12-point plan that describes the initiative, current capabilities and data collected, and impacts to the program including staff and budget.

The draft 12-point plan provides a complete description of the methods and studies that have been conducted by the WSLH. The PO and WSLH have developed procedures that require minimal infrastructure and operational requirements which has made it attractive for existing sites to join the Mercury Passive pilot network.

The 12-point plan was presented to the committees during the Fall 2024 Business Meeting. The Executive Committee approved the motion to establish a pilot network for 1-year. During this period the WSLH TECL and the NADP PO will further develop and document procedures for efficient generation and reporting of passive mercury gaseous elemental mercury concentration data from the laboratory.

During the 1-year pilot period, advocates will promote the network and identify parties that are interested in joining and expanding the current pilot network.

At a future NADP business meeting, the advocates will present results and any updates to the established 12-point plan. If appropriate, the advocates will ask the Executive Committee to transition the pilot network to an official network within the NADP or request an extension to the current pilot network for an additional year.

• McLagan, D. S., Mitchell, C. P., Huang, H., Lei, Y. D., Cole, A. S., Steffen, A., … & Wania, F. (2016). A high-precision passive air sampler for gaseous mercury. Environmental Science & Technology Letters, 3(1), 24-29. DOI: https://doi.org/10.1021/acs.estlett.5b00319
• McLagan, D. S., Monaci, F., Huang, H., Lei, Y. D., Mitchell, C. P., & Wania, F. (2019). Characterization and quantification of atmospheric mercury sources using passive air samplers. Journal of Geophysical Research: Atmospheres, 124(4), 2351-2362. DOI: http://dx.doi.org/10.1029/2018JD029373
• McLagan, D. S., Mazur, M. E., Mitchell, C. P., & Wania, F. (2016). Passive air sampling of gaseous elemental mercury: a critical review. Atmospheric Chemistry and Physics, 16(5), 3061-3076. DOI: https://doi.org/10.5194/acp-16-3061-2016
• McLagan, D. S., Mitchell, C. P., Huang, H., Abdul Hussain, B., Lei, Y. D., & Wania, F. (2017). The effects of meteorological parameters and diffusive barrier reuse on the sampling rate of a passive air sampler for gaseous mercury. Atmospheric Measurement Techniques, 10(10), 3651-3660.DOI: https://doi.org/10.5194/amt-10-3651-2017
• McLagan, D. S., Mitchell, C. P., Steffen, A., Hung, H., Shin, C., Stupple, G. W., … & Wania, F. (2018). Global evaluation and calibration of a passive air sampler for gaseous mercury. Atmospheric Chemistry and Physics, 18(8), 5905-5919. DOI: https://doi.org/10.5194/acp-18-5905-2018

• Powerpoint deck
• Recording