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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 18, issue 8
Atmos. Chem. Phys., 18, 5905-5919, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Atmos. Chem. Phys., 18, 5905-5919, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 26 Apr 2018

Research article | 26 Apr 2018

Global evaluation and calibration of a passive air sampler for gaseous mercury

David S. McLagan1, Carl P. J. Mitchell1, Alexandra Steffen2, Hayley Hung2, Cecilia Shin2, Geoff W. Stupple2, Mark L. Olson3, Winston T. Luke4, Paul Kelley4, Dean Howard5, Grant C. Edwards5, Peter F. Nelson5, Hang Xiao6, Guey-Rong Sheu7, Annekatrin Dreyer8, Haiyong Huang1, Batual Abdul Hussain1, Ying D. Lei1, Ilana Tavshunsky1, and Frank Wania1 David S. McLagan et al.
  • 1Department of Physical and Environmental Sciences, University of Toronto Scarborough, Toronto, M1C 1A4, Canada
  • 2Air Quality Processes Research Section, Environment and Climate Change Canada, Toronto, M3H 5T4, Canada
  • 3Atmospheric Mercury Network, National Atmospheric Deposition Network, Champaign, 61820-7495, USA
  • 4Air Resources Lab, National Oceanic and Atmospheric Administration, Maryland, 20740, USA
  • 5Department of Environmental Sciences, Macquarie University, Sydney, 2109, Australia
  • 6Center for Excellence in Regional Atmospheric Environment, Institute of Urban Environment, Xiamen, 361021, China
  • 7Department of Atmospheric Sciences, National Central University, Taoyuan City, 32001, Taiwan
  • 8Air Monitoring, Eurofins GfA, Hamburg, 21107, Germany

Abstract. Passive air samplers (PASs) for gaseous mercury (Hg) were deployed for time periods between 1 month and 1 year at 20 sites across the globe with continuous atmospheric Hg monitoring using active Tekran instruments. The purpose was to evaluate the accuracy of the PAS vis-à-vis the industry standard active instruments and to determine a sampling rate (SR; the volume of air stripped of gaseous Hg per unit of time) that is applicable across a wide range of conditions. The sites spanned a wide range of latitudes, altitudes, meteorological conditions, and gaseous Hg concentrations. Precision, based on 378 replicated deployments performed by numerous personnel at multiple sites, is 3.6±3.0%1, confirming the PAS's excellent reproducibility and ease of use. Using a SR previously determined at a single site, gaseous Hg concentrations derived from the globally distributed PASs deviate from Tekran-based concentrations by 14.2±10%. A recalibration using the entire new data set yields a slightly higher SR of 0.1354±0.016m3day−1. When concentrations are derived from the PAS using this revised SR the difference between concentrations from active and passive sampling is reduced to 8.8±7.5%. At the mean gaseous Hg concentration across the study sites of 1.54ngm−3, this represents an ability to resolve concentrations to within 0.13ngm−3. Adjusting the sampling rate to deployment specific temperatures and wind speeds does not decrease the difference in active–passive concentration further (8.7±5.7%), but reduces its variability by leading to better agreement in Hg concentrations measured at sites with very high and very low temperatures and very high wind speeds. This value (8.7±5.7%) represents a conservative assessment of the overall uncertainty of the PAS due to inherent uncertainties of the Tekran instruments. Going forward, the recalibrated SR adjusted for temperature and wind speed should be used, especially if conditions are highly variable or deviate considerably from the average of the deployments in this study (9.89°C, 3.41ms−1). Overall, the study demonstrates that the sampler is capable of recording background gaseous Hg concentrations across a wide range of environmental conditions with accuracy similar to that of industry standard active sampling instruments. Results at sites with active speciation units were inconclusive on whether the PASs take up total gaseous Hg or solely gaseous elemental Hg primarily because gaseous oxidized Hg concentrations were in a similar range as the uncertainty of the PAS.

1Subscripted numbers are not significant, but are reported to reduce rounding errors in subsequent studies (see Sect. 2.3 for details).

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Short summary
A new passive air sampler for gaseous mercury was tested at 20 sites on four continents. These sites have in common that they use the state-of-the-art active air sampling technique for gaseous mercury on a continuous basis and therefore allow for an evaluation and calibration of the passive sampler. The sampler proved to work exceptionally well, with a precision and accuracy on par with the active instrument and better than what has previously been achieved with passive samplers.
A new passive air sampler for gaseous mercury was tested at 20 sites on four continents. These...