Abstract
Abstract. The National Atmospheric Deposition Program (NADP) developed and operates a collaborative network of atmospheric-mercury-monitoring sites based in North America – the Atmospheric Mercury Network (AMNet). The justification for the network was growing interest and demand from many scientists and policy makers for a robust database of measurements to improve model development, assess policies and programs, and improve estimates of mercury dry deposition. Many different agencies and groups support the network, including federal, state, tribal, and international governments, academic institutions, and private companies. AMNet has added two high-elevation sites outside of continental North America in Hawaii and Taiwan because of new partnerships forged within NADP. Network sites measure concentrations of atmospheric mercury fractions using automated, continuous mercury speciation systems. The procedures that NADP developed for field operations, data management, and quality assurance ensure that the network makes scientifically valid and consistent measurements. AMNet reports concentrations of hourly gaseous elemental mercury (GEM), two-hour gaseous oxidized mercury (GOM), and two-hour particulate-bound mercury less than 2.5 microns in size (PBM2.5). As of January 2012, over 450 000 valid observations are available from 30 stations. AMNet also collects ancillary meteorological data and information on land use and vegetation, when available. We present atmospheric mercury data comparisons by time (3 yr) at 21 individual sites and instruments. Highlighted are contrasting values for site locations across the network: urban versus rural, coastal versus high elevation and the range of maximum observations. The data presented should catalyze the formation of many scientific questions that may be answered through further in-depth analysis and modeling studies of the AMNet database. All data and methods are publically available through an online database on the NADP website (http://nadp.sws.uiuc.edu/amn/). Future network directions are to foster new network partnerships and continue to collect, quality assure, and post data, including dry deposition estimates, for each fraction.
Highlights
The current Mercury Deposition Network (MDN), initiated in the mid-1990s, provides data on the concentration of total mercury (Hg) in precipitation at 110 sites across North America
MDN is one of five networks of the National Atmospheric Deposition Program (NADP), which monitors the rate of pollutant removal from the atmosphere and deposition loadings to ecosystems
Based on atmospheric model estimates and several field studies, the dry deposition of Hg has been estimated to be wide ranging relative to wet deposition
Summary
The current Mercury Deposition Network (MDN), initiated in the mid-1990s, provides data on the concentration of total mercury (Hg) in precipitation at 110 sites across North America. When the NADP membership began considering an atmospheric Hg network in 2004, the most promising and available approach to estimate dry deposition in select locations was high-resolution, continuously measured concentrations of atmospheric Hg fractions, combined with modeled deposition parameters. Over 100 scientists contributed to the current instrument selection, development of equipment operating procedures, and data management methods adopted for use in AMNet. AMNet uses automated, continuous measuring systems to measure the atmospheric Hg fractions GEM, GOM, and PBM2.5. We report here for the first time an accessible, standardized North American database of atmospheric Hg measurements that should provide for future trend analysis, model development, and total mercury deposition estimates. We report on three years of observations from a number of monitoring locations and site groupings, compare and contrast the results, and identify several research questions as yet unanswered
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