Testing the use of passive sampling systems for understanding air mercury concentrations and dry deposition across Florida, USA.

This paper describes the use of passive sampling systems and surrogate surfaces for monitoring atmospheric mercury (Hg) concentrations and dry deposition, respectively, in Florida,USA. Although this area has been reported to have low air concentrations, wet deposition values, reported by the Mercury Deposition Network, are some of the highest in the United States, and little is known about the magnitude of dry deposition to the region. To address this uncertainty, dry deposition of gaseous oxidized mercury (GOM) was estimated based on data collected using surrogate surfaces and through the application of a dry deposition model that utilized Tekran® Mercury Analyzer data for three sites (Davie near Fort Lauderdale, Tampa and Pensacola) over a year (July 2009-July 2010). Passive sampler systems for monitoring GOM and total gaseous mercury (TGM) concentrations were also deployed. In general, higher surrogate surface deposition, and GOM and TGM passive sampler uptake were observed at the DVE location. Across all sites, empirically derived dry deposition was higher than that determined using modeled values. Tekran® Instrument derived GOM concentrations, as well as modeled deposition rates, followed the same seasonal and spatial patterns as that measured by the samplers, however there were some spatial and temporal trends captured by the samplers that were not seen in the Tekran® derived data. Results indicate that these samplers may be applied to identify spatial and temporal trends in air Hg concentrations and potential deposition at sites with low and fairly constant GOM concentrations as reported by the Tekran® system (2-8 pg m(-3)). When viewed collectively, trends in sampler and Tekran® derived data also suggest the potential for different forms of GOM in air. Using empirical and modeled values, dry deposition in Florida during the year of this study could account for 1.5 to 14% of total annual Hg deposition (wet+dry).