The Atmospheric Mercury Network (AMNet) established this network of monitoring stations for the purpose of measuring atmospheric mercury fractions which contribute to dry and total mercury deposition. Sites will collect concentrations of atmospheric mercury species from automated, continuous measuring systems, concentrations of total mercury in precipitation, and meteorological measurements. Data will be collected with standardized methods, with quality assured data archived in an online data base.
Note: In May 2025, the Executive Committee approved the motion to discontinue support of Tekran speciation measurements by the end of current site contracts, at the discretion of the Program Office (PO). The PO will provide sites that want to continue speciation measurements with the data validation program for the GOM/PBM measurements.
AMNet has specific objectives:
- Measure atmospheric mercury concentrations of elemental mercury in select locations
- Offer high-quality measurement data to estimate dry and total deposition of atmospheric mercury to other researchers
- Standardized operational methods so that instruments are being operated consistently
- Provide internal and external quality assurance
- Provide the data management capability and access
- Provide field support through an experienced site liaison
As with other networks, NADP welcomes the participation of other organizations and scientists. To truly understand the mercury problem, more monitoring information is needed.
Information on joining the network is available here.
Data Notices
Notification: The Program Office is alerting data users that the Gaseous Oxidized Mercury (GOM) and Particulate-bound Mercury (PBM) measurements were discontinued in 2025 and that the data provided on the website include a known bias in GOM/PBM.
Metadata
Maps / GIS
Annual Boxplots
The annual boxplots show the distribution of all valid measurements of Gaseous Elemental Mercury (GEM), Gaseous Oxidized Mercury (GOM), and Particulate Bound Mercury (PBM2.5) over the course of the entire calendar year. The GOM and PBM2.5 is a direct measurement from a collection span of 2 hours (with some 1 hour measurements). The GEM is an average of 12 measurements taken over the course of an hour, for every third hour.
Prior to 2018, the boxplots use a linear scale for the Y axis, and typically display the following distribution values:
- Median (50th percentile)
- 25th and 75th percentiles delineated by the box (middle 50% of the data)
- 5th and 95th percentile observations delineated by the boxplot whiskers
- Extreme 5% of observations within the graph limits shown by the circles
Starting in 2018, the boxplots use a logarithmic scale for the Y axis, and display the following distribution values:
- Mean
- Median (50th percentile)
- 25th and 75th percentiles delineated by the box (middle 50% of the data)
- 10th and 90th percentile observations delineated by the boxplot whiskers
- Extreme 10% of observations on both higher and lower ends of the boxplot shown by the circles
Boxplot requirements and methods have changed over time, which can change the appearance from year to year. Individual boxplot descriptions from the Annual Summary documents have been copied here, and may also be found in the annual summaries in the publication section of this web site.
Please read our Use Conditions. before including these maps in publications.
Field Methods
Monitoring and analysis of elemental, gaseous oxidized and particulate Mercury fractions use a 2.5-micrometer impactor and KCl-coated annular denuder (for ionic mercury), thermally-desorbed particulate filter (for particulate-bound mercury), and gold traps (for elemental mercury). Analysis uses cold vapor atomic fluorescence spectroscopy (CVAFS).