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Volume 16, issue 7 | Copyright

Special issue: Data collection, analysis and application of speciated atmospheric...

Atmos. Chem. Phys., 16, 4451-4480, 2016
https://doi.org/10.5194/acp-16-4451-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Review article 11 Apr 2016

Review article | 11 Apr 2016

Global observations and modeling of atmosphere–surface exchange of elemental mercury: a critical review

Wei Zhu1,2, Che-Jen Lin1,3, Xun Wang1, Jonas Sommar1, Xuewu Fu1, and Xinbin Feng1 Wei Zhu et al.
  • 1State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China
  • 2Department of Chemistry, Umeå University, 901 87 Umeå, Sweden
  • 3Center for Advances in Water and Air Quality, Lamar University, Beaumont, Texas 77710, USA

Abstract. Reliable quantification of air–surface fluxes of elemental Hg vapor (Hg0) is crucial for understanding mercury (Hg) global biogeochemical cycles. There have been extensive measurements and modeling efforts devoted to estimating the exchange fluxes between the atmosphere and various surfaces (e.g., soil, canopies, water, snow, etc.) in the past three decades. However, large uncertainties remain due to the complexity of Hg0 bidirectional exchange, limitations of flux quantification techniques and challenges in model parameterization. In this study, we provide a critical review on the state of science in the atmosphere–surface exchange of Hg0. Specifically, the advancement of flux quantification techniques, mechanisms in driving the air–surface Hg exchange and modeling efforts are presented. Due to the semi-volatile nature of Hg0 and redox transformation of Hg in environmental media, Hg deposition and evasion are influenced by multiple environmental variables including seasonality, vegetative coverage and its life cycle, temperature, light, moisture, atmospheric turbulence and the presence of reactants (e.g., O3, radicals, etc.). However, the effects of these processes on flux have not been fundamentally and quantitatively determined, which limits the accuracy of flux modeling.

We compile an up-to-date global observational flux database and discuss the implication of flux data on the global Hg budget. Mean Hg0 fluxes obtained by micrometeorological measurements do not appear to be significantly greater than the fluxes measured by dynamic flux chamber methods over unpolluted surfaces (p = 0.16, one-tailed, Mann–Whitney U test). The spatiotemporal coverage of existing Hg0 flux measurements is highly heterogeneous with large data gaps existing in multiple continents (Africa, South Asia, Middle East, South America and Australia). The magnitude of the evasion flux is strongly enhanced by human activities, particularly at contaminated sites. Hg0 flux observations in East Asia are comparatively larger in magnitude than the rest of the world, suggesting substantial re-emission of previously deposited mercury from anthropogenic sources. The Hg0 exchange over pristine surfaces (e.g., background soil and water) and vegetation needs better constraints for global analyses of the atmospheric Hg budget. The existing knowledge gap and the associated research needs for future measurements and modeling efforts for the air–surface exchange of Hg0 are discussed.

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Reliable quantification of air-surfaces flux of elemental mercury vapor (Hg0) is crucial for understanding Hg global biogeochemical cycles. In this study, we provide a comprehensive review on the state of science in the atmosphere-surface exchange of elemental Hg. We compiled an up-to-date global observational flux database and discuss the implication of flux data on global Hg budget. The knowledge gap and research needs for future measurements and modeling efforts were discussed.
Reliable quantification of air-surfaces flux of elemental mercury vapor (Hg0) is crucial for...
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