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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
doi:10.5194/acp-2017-307
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
21 Apr 2017
Review status
This discussion paper is under review for the journal Atmospheric Chemistry and Physics (ACP).
Atmospheric mercury in the southern hemisphere tropics: seasonal and diurnal variations and influence of inter-hemispheric transport
Dean Howard1, Peter F. Nelson1, Grant C. Edwards1, Anthony L. Morrison1, Jenny A. Fisher2,3, Jason Ward4, James Harnwell4, Marcel van der Schoot4, Brad Atkinson5, Scott D. Chambers6, Alan D. Griffiths6, Sylvester Werczynski6, and Alastair G. Williams6 1Department of Environmental Sciences, Macquarie University, Sydney, New South Wales, 2109, Australia
2Centre for Atmospheric Chemistry, School of Chemistry, University of Wollongong, Wollongong, New South Wales, 2552, Australia
3School of Earth & Environmental Sciences, University of Wollongong, Wollongong, New South Wales, 2552, Australia
4Oceans and Atmosphere Flagship, Commonwealth Science and Industrial Research Organisation, Aspendale, Victoria, 3195, Australia
5Darwin Research Station, Bureau of Meteorology, Darwin, Northern Territory, 0810, Australia
6Institute for Environmental Research, Australian Nuclear Science and Technology Organisation, Sydney, New South Wales, 2232, Australia
Abstract. Mercury is a toxic element of serious concern for human and environmental health. Understanding its natural cycling in the environment is an important goal towards assessing its impacts and the effectiveness of mitigation strategies. Due to the unique chemical and physical properties of mercury, the atmosphere is the dominant transport pathway for this heavy metal, with the consequence that regions far removed from sources can be impacted. However, there exists a dearth of long-term monitoring of atmospheric mercury, particularly in the tropics and southern hemisphere. This paper presents the first two years of gaseous elemental mercury (GEM) measurements taken at the Australian Tropical Atmospheric Research Station (ATARS) in northern Australia, as part of the Global Mercury Observation System (GMOS). Annual mean GEM concentrations determined at ATARS (0.95 ± 0.12 ng m−3) are consistent with recent observations at other sites in the southern hemisphere. Comparison with GEM data from other Australian monitoring sites suggests a concentration gradient that decreases with increasing latitude. Seasonal analysis shows that GEM concentrations at ATARS are significantly lower in the distinct wet monsoon season than in the dry season. This result provides insight into alterations of natural mercury cycling processes as a result of changes in atmospheric humidity, oceanic/terrestrial fetch and convective mixing, and invites future investigation using wet mercury deposition measurements. Due to its location relative to the atmospheric equator, ATARS intermittently samples air originating from the northern hemisphere, allowing an opportunity to gain greater understanding of inter-hemispheric transport of mercury and other atmospheric species. Diurnal cycles of GEM at ATARS show distinct nocturnal depletion events that are attributed to dry deposition under stable boundary layer conditions. These cycles provide strong further evidence for the multi-hop model of global GEM cycling, whereby long-range transport is characterised by multiple surface depositions and re-emissions, rather than continuous transport over long distances.

Citation: Howard, D., Nelson, P. F., Edwards, G. C., Morrison, A. L., Fisher, J. A., Ward, J., Harnwell, J., van der Schoot, M., Atkinson, B., Chambers, S. D., Griffiths, A. D., Werczynski, S., and Williams, A. G.: Atmospheric mercury in the southern hemisphere tropics: seasonal and diurnal variations and influence of inter-hemispheric transport, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2017-307, in review, 2017.
Dean Howard et al.
Dean Howard et al.
Dean Howard et al.

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Short summary
Mercury, a toxic metal, can be transported in the atmosphere hundreds of kilometres from sources. Limited equatorial mixing and less sources result in lower concentrations in the southern hemisphere (SH). Our 2 years of monitoring supports recent evidence that SH concentrations are lower than previously thought and highlights a pathway for mercury from the atmosphere to ecosystems. This research can be used to develop/assess models and mitigation strategies aimed at reducing impacts of mercury.
Mercury, a toxic metal, can be transported in the atmosphere hundreds of kilometres from...
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