Abstract
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.
Highlights
It is essential that we characterise mercury (Hg) emissions to the atmosphere with constrained uncertainties as the atmosphere is the primary pathway for the global redistribution of Hg, a pollutant with considerable environmental and human health implications (UNEP 2013, Driscoll et al 2013)
This study examines Gaseous elemental mercury (GEM) concentrations measured with MerPAS and Tekran 2537A instruments in and around a legacy site contaminated with Hg-containing waste materials in Switzerland
The 5-min sampling resolution of the active instrument allows assessment of shortterm temporal variability in GEM concentrations that cannot be made with the passive samplers that provide concentrations averaged across the whole time they are deployed
Summary
It is essential that we characterise mercury (Hg) emissions to the atmosphere with constrained uncertainties as the atmosphere is the primary pathway for the global redistribution of Hg, a pollutant with considerable environmental and human health implications (UNEP 2013, Driscoll et al 2013). Two main approaches exist for estimating emissions from such sites: (i) upscaling of in situ terrestrial substrate-to-atmosphere flux measurements (Engle et al 2001, Wang et al2005), or (ii) top-down or inverse-modelling approaches based on atmospheric Hg concentration measurements (typically using active monitoring instruments or satellite spectra) that are elevated above background at these sites (Ferrara et al 1998, Song et al 2015) These methods of emissions estimations have elevated uncertainties associated with the instrumentation, poor spatial distribution of sampling (limited instrument mobility: non-representative sampling), and non-concurrent measurements (introduce temporal concentration variability), (Kocman et al 2013, Zhu et al 2015, Agnan et al 2016, McLagan et al 2019)
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