This collaborative award will support an inter-comparison of different measurement systems for atmospheric mercury (Hg). Hg is an important neurotoxin which bioaccumulates in the food chain. It is an important global pollutant and the atmosphere is a key site for processing and global transport. However, there are large uncertainties in our understanding of the atmospheric cycling of Hg, in part due to significant uncertainties in its measurement.
The experimental campaign will occur during the summer of 2011 at a site in Reno Nevada that has previously been used for Hg research, and will involve four new measurement systems along with the traditional method system that is currently widely in use for Hg. The new methods will be compared and challenged using a carefully designed manifold for spiking and interference tests. The specific goals for this project are: (1) to compare ambient measurements of gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM) and particulate mercury (PHg) by multiple groups for four weeks; (2) to examine the response of all systems to spikes of elemental Hg and mercury halides; (3) to examine the response to Hg of all systems in the presence of known or potential interfering compounds, including ozone, water vapor and other compounds; (4) to analyze the data to quantify the level of agreement and the results of interference and calibration tests for each measurement system; and (5) to publish the results in the peer-reviewed literature.
This project is aimed at improving the measurement capabilities for a very important pollutant. The development and testing of better methods to measure Hg follows on the recommendations of several national assessments and an NSF supported workshop. This project will provide training opportunities for a number of undergraduates, graduate students and post-doctoral fellows.
The Reno Atmospheric Mercury Intercomparison eXperiment (RAMIX) project was held at an inactive Hg Deposition Network (MDN, http://nadp.sws.uiuc.edu/mdn) site, MDN NV98, located on the University of Nevada-Reno (UNR) Agricultural Experiment Station property (39.51° latitude,−119.72° longitude, elevation 1340 m). The objective of the project was to compared observations made by multiple systems configured to measure atmospheric mercury(Hg), including the traditional Tekran® system, widely in use over the past ~10 years for atmospheric Hg measurements. Major participating groups included the University of Nevada-Reno, University of Washington-Bothell, University of Houston, Desert Research Institute, and University of Miami. A manifold system, by which elemental Hg, mercuric bromide (HgBr2), ozone, and water vapor could be spiked into ambient air and subsequently sampled by all units, was designed by the University of Washington group, and operated independently of all groups during the experiment. This was the first experiment to measure atmospheric Hg while spiking elemental Hg, HgBr2, ozone, and water vapor into a manifold in the field. Over the course of the four week experiment atmospheric Hg was measured by the UNR group using one Tekran® 2537 unit and two Tekran® 2537/1130/1135 systems. UNR also operated a filter based air Hg sampling system. UNR began preparation for this project several months before the start of the experiment. This included, through collaboration with the Nevada Division of Environmental Protection and UNR electricians, establishing two air-sampling trailers and the UNR equipment on site, and configuring the electricity and connections needed by the participants. We also coordinated receipt of non-UNR equipment, site breakdown, and shipment of equipment back to their respective home. During the project, UNR operated two Tekran® 2537/1130/1135 atmospheric Hg speciation systems, a Tekran® 2537 unit, two ozone analyzers, a carbon monoxide (CO) analyzer, and meteorological equipment. UNR performed all quality control necessary for these instruments. UNR was also responsible for checking the manifold system operating conditions (i.e. flows, temperature) during the experiment, as well as configuring and managing the spiking schedule. UNR supplied field and laboratory support as needed by the other groups participating in the project. The UNR group, along with other scientists that collaborated on this project, is currently completing a manuscript that: 1- Compares atmospheric mercury data obtained by the various groups during the four-week experiment; 2- Examines the responses of the Tekran® systems to spikes of elemental Hg and HgBr2; 3- Examines the responses of the Tekran® systems to spikes of ozone and water vapor; and 4- Analyzes the data to quantify the level of agreement between Tekran®-based instruments and the responses to interference tests. Spike recoveries were calculated using data collected simultaneously by one freestanding instrument (not connected to the manifold) and one connected to the sampling manifold. Using the Tekran® data, gaseous elemental Hg spike recoveries were ~76 + 7%, while those for HgBr2 were 17 + 3%. Ozone and water vapor spike recoveries ranged from 81 to 95% and 88 to 110%, respectively. The low HgBr2 recovery by the Tekran® system could be attributed to loss of the spike in the manifold, low recovery by the Tekran® system as configured, and/or ozone or water vapor interferences. Collectively, the data generated provide a framework for improved understanding of Tekran ® Hg measurements and the atmospheric chemistry of Hg.
