Applying Passive Air Sampling and Isotopic Characterization to Assess Spatial Variability of Gaseous Elemental Mercury Across Ontario, Canada

• Published in: Journal of geophysical research. Atmospheres 2023-02, Vol.128 (3), p.n/a
• Main Authors: Szponar, Natalie, Su, Yushan, Stupple, Geoff, McLagan, David S., Pilote, Martin, Munoz, Anthony, Mitchell, Carl P. J., Steffen, Alexandra, Wania, Frank, Bergquist, Bridget A.
• Format: Article
• Language: English
• Subjects: Air sampling; Atmosphere; Atmospheric mercury; Boreal forests; Chemical composition; Emission; Emissions; Forests; Geophysics; Industrial areas; Industrial emissions; Isotope composition; Isotopes; Lower atmosphere; Lowlands; Mercury; Mercury isotopes; Peat; Samplers; Spatial variability; Spatial variations; Taiga; Uptake; Variability; Vegetation
• ISSN: 2169-897X; 2169-8996
• DOI: 10.1029/2022JD037361

This study deployed 59 passive air samplers (PAS) across the province of Ontario, Canada (and eight additional deployments in bordering states of northern USA) to assess the influence of local/regional sources, temporal differences, and possible transformations in the atmospheric gaseous elemental mercury (GEM) pool. The spatial mapping achieved with the PASs allowed for the observation of differences in GEM and its isotopic composition over the region. Concentrations of GEM were higher with more negative δ202Hg values near urban/industrial areas and suspected emission sources in southern Ontario. In northern Ontario, far from industrial influences, lower concentrations of GEM with isotopically more positive δ202Hg values were found at the boreal forest sites compared to sites within the Hudson Bay Lowlands. The differences in northern Ontario may be from greater uptake of GEM by the boreal forest removing isotopically light Hg and lowering concentrations. Lower GEM and a shift toward more positive δ202Hg were also observed during the summer relative to other times of year supporting vegetation uptake as an important sink for GEM. PASs were also deployed along a transect of increasing distance from a Hg recycling facility. The Hg emissions from the facility had unique positive Δ199Hg and Δ200Hg signatures, but GEM concentrations and isotopic compositions returned to background within 400 m of the facility. The province‐wide variations in atmospheric GEM and isotopic compositions show that both sources (e.g., urban/industrial emissions) and sinks (e.g., vegetation uptake) contribute to the spatial and temporal patterns of the residual atmosphere GEM pool. Plain Language Summary Gaseous elemental mercury (GEM) is the most dominant form of mercury in the atmosphere. Passive air samplers were used in a large regional‐wide study across Ontario to collect samples of atmospheric GEM at over 60 sites. The goals of the study were to evaluate variability in atmospheric GEM across Ontario and to assess how mercury sources, transformations, and sinks contribute to variability of GEM on local and regional scales using stable mercury isotopes. Compared to northern Ontario, GEM collected in southern Ontario had higher GEM levels with isotope compositions influenced by urban/industrial emission sources. Overall, northern Ontario had lower GEM levels consistent with the region having fewer emission sources and being mostly forest covered. However, at far‐northern Ontario s