Temporal and spatial assessment of gaseous elemental mercury concentrations and emissions at contaminated sites using active and passive measurements

Gaseous elemental mercury (GEM) concentrations and emissions at legacy contaminated sites represent poorly characterised components of global mercury (Hg) inventories. Here we apply both active (Tekran 2537A) and passive (MerPAS) sampling methods to comprehensively assess GEM concentrations and emissions across four dimensions (three spatial, one temporal) at a legacy contaminated site with elevated soil Hg. Concentrations are measured up to 37.4 (active) and 10.8 (passive) ng m−3, which represents enhancements of 23× and 7× above background (1.62 ng m−3), respectively. Temporal resolution of the sampling methods defines this difference (active: 5-min; passive: 44 days). Diurnal (active) GEM concentration patterns were highest in contaminated areas at night when low wind speeds compress the boundary layer. Passive sampling substantially improves the spatial characterisation of GEM concentrations both horizontally (highest GEM concentration in areas with elevated soil Hg) and vertically (improved vertical concentration gradient using telescopic sampling towers). Passive sampler deployments were used to generate a GEM emissions estimate (landfill-to-atmosphere) of 1.2 ± 0.6 kg yr−1 (or 310 ± 150 ng m−2 h−1). This study demonstrates how combining active (strength: temporal assessment) and passive (strength: spatial assessments) sampling improves the evaluation of GEM concentrations and emissions to the atmosphere at Hg contaminated sites across four dimensions.