Atmospheric mercury speciation in Yellowstone National Park

Atmospheric concentrations of elemental mercury (Hg⁰), reactive gaseous Hg (RGM), and particulate Hg (pHg) concentrations were measured in Yellowstone National Park (YNP), U.S.A. using high resolution, real time atmospheric mercury analyzers (Tekran 2537A, 1130, and 1135). A survey of Hg⁰ concentrations at various locations within YNP showed that concentrations generally reflect global background concentrations of 1.5–2.0 ng m^− 3, but a few specific locations associated with concentrated geothermal activity showed distinctly elevated Hg⁰ concentrations (about 9.0 ng m^− 3). At the site of intensive study located centrally in YNP (Canyon Village), Hg⁰ concentrations did not exceed 2.5 ng m^− 3; concentrations of RGM were generally below detection limits of 0.88 pg m^− 3 and never exceeded 5 pg m^− 3. Concentrations of pHg ranged from below detection limits to close to 30 pg m⁻³. RGM and pHg concentrations were not correlated with any criteria gases (SO₂, NO_x, O₃); however pHg was weakly correlated with the concentration of atmospheric particles. We investigated three likely sources of Hg at the intensive monitoring site: numerous geothermal features scattered throughout YNP, re-suspended soils, and wildfires near or in YNP. We examined relationships between the chemical properties of aerosols (as measured using real time, single particle mass spectrometry; aerosol time-of-flight mass spectrometer; ATOFMS) and concentrations of atmospheric pHg. Based on the presence of particles with distinct chemical signatures of the wildfires, and the absence of signatures associated with the other sources, we concluded that wildfires in the park were the main source of aerosols and associated pHg to our sampling site.