Articles | Volume 9, issue 2
Atmos. Meas. Tech., 9, 509–524, 2016
Atmos. Meas. Tech., 9, 509–524, 2016

Research article 15 Feb 2016

Research article | 15 Feb 2016

A dual-inlet, single detector relaxed eddy accumulation system for long-term measurement of mercury flux

S. Osterwalder1, J. Fritsche1, C. Alewell1, M. Schmutz1, M. B. Nilsson2, G. Jocher2, J. Sommar3, J. Rinne4,5, and K. Bishop6,7 S. Osterwalder et al.
  • 1Department of Environmental Sciences, University of Basel, Basel, Switzerland
  • 2Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden
  • 3State Key Laboratory of Environmental Geochemistry, Chinese Academy of Sciences, Guiyang, China
  • 4Department of Geosciences and Geography, University of Helsinki, Helsinki, Finland
  • 5Finnish Meteorological Institute, Helsinki, Finland
  • 6Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden
  • 7Department of Earth Sciences, University of Uppsala, Uppsala, Sweden

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.

Short summary
Human activities have increased mercury (Hg) cycling between land and atmosphere. To define landscapes as sinks or sources of Hg we have developed an advanced REA system for long-term measurements of gaseous elemental Hg exchange. It was tested in two contrasting environments: above Basel, Switzerland, and a peatland in Sweden. Both landscapes showed net Hg emission (15 and 3 ng m−2 h−1, respectively). The novel system will help to advance our understanding of Hg exchange on an ecosystem scale.