Atmospheric Mercury Instrument Intercomparison
U.S. Geological Survey,
Middleton, WI USA
The USGS and USEPA conducted an assessment of instrument performance to determine the concentration of mercury fractions in the atmosphere. Four atmospheric speciation systems were compared which continuously measure gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and fine-fraction particulate-bound mercury (PBM2.5) respectively. The study was conducted at a warehouse facility the USGS uses for instrument set up and testing. Instrument intakes were connected to a common high flow, unheated manifold and inlet concentrations were varied to create dynamic conditions simulating variability observed in the field. Accuracy of the GOM thermal desorption, line transfer and quantification was evaluated both in the warehouse and the field using pre-spiked denuders with a known loading of HgCl2.
Results from the dynamic testing showed elemental and particulate mercury percent relative standard deviation was less than 10%, although gaseous oxidized mercury was higher, around 18%. Denuder spiking results were better (11% RSD) suggesting a portion of the variability for gaseous oxidized mercury may be due to variations in the intake gas. The specific challenges of intercomparisons of low level mercury speciation measurements will be presented.