Abstract
Abstract. The fate of anthropogenic emissions of mercury (Hg) to the atmosphere is influenced by the exchange of elemental Hg with the earth surface. This exchange holds the key to a better understanding of Hg cycling from local to global scales, which has been difficult to quantify. To advance research about land–atmosphere Hg interactions, we developed a dual-inlet, single detector relaxed eddy accumulation (REA) system. REA is an established technique for measuring turbulent fluxes of trace gases and aerosol particles in the atmospheric surface layer. Accurate determination of gaseous elemental mercury (GEM) fluxes has proven difficult due to technical challenges presented by extremely small concentration differences (typically < 0.5 ng m−3) between updrafts and downdrafts. We present an advanced REA design that uses two inlets and two pairs of gold cartridges for continuous monitoring of GEM fluxes. This setup reduces the major uncertainty created by the sequential sampling in many previous designs. Additionally, the instrument is equipped with a GEM reference gas generator that monitors drift and recovery rates. These innovations facilitate continuous, autonomous measurement of GEM flux. To demonstrate the system performance, we present results from field campaigns in two contrasting environments: an urban setting with a heterogeneous fetch and a boreal peatland during snowmelt. The observed average emission rates were 15 and 3 ng m−2 h−1, respectively. We believe that this dual-inlet, single detector approach is a significant improvement of the REA system for ultra-trace gases and can help to advance our understanding of long-term land–atmosphere GEM exchange.
Highlights
The UN’s legally binding Minimata Convention has been signed by 128 countries since October 2013 and aims to protect human health and welfare by reducing anthropogenic release of mercury (Hg) into the environment (UNEP, 2013a)
Zhu et al (2015b) found that the calculation of concentration differences based on temporally intermittent gaseous elemental mercury (GEM) measurements introduced the largest source of uncertainty in their singleinlet Hg0-relaxed eddy accumulation (REA) system
Accurate simultaneous sampling of GEM concentration using a two-inlet design is the major technical improvement of our system compared to most Hg-REA systems used to date, as summarized in Sommar www.atmos-meas-tech.net/9/509/2016/
Summary
The UN’s legally binding Minimata Convention has been signed by 128 countries since October 2013 and aims to protect human health and welfare by reducing anthropogenic release of mercury (Hg) into the environment (UNEP, 2013a). Additional 10 % comes from natural geological sources and the remaining 60 % from re-emission of previously deposited Hg (UNEP, 2013b). Long-range atmospheric transport of gaseous elemental mercury (GEM or Hg0) has led to Hg deposition and accumulation in soils and water bodies well in excess of natural levels even in remote areas, far away from anthropogenic pollution sources (Grigal, 2002; Slemr et al, 2003). Gustin et al (2008) suggest that today a substantial amount of Hg deposited on soils with natural background concentrations of Hg (< 0.1 μg g−1) is re-emitted back to the atmosphere and that over the course of a year deposition is largely compensated for by re-emission, resulting in a net flux close to 0 Osterwalder et al.: A dual-inlet, single detector relaxed eddy accumulation system tion targeting the control of Hg emissions (Lindberg et al, 2007). Gustin et al (2008) suggest that today a substantial amount of Hg deposited on soils with natural background concentrations of Hg (< 0.1 μg g−1) is re-emitted back to the atmosphere and that over the course of a year deposition is largely compensated for by re-emission, resulting in a net flux close to 0
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