Articles | Volume 17, issue 18
Atmos. Chem. Phys., 17, 11623–11636, 2017
Atmos. Chem. Phys., 17, 11623–11636, 2017

Research article 28 Sep 2017

Research article | 28 Sep 2017

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 Dean Howard et al.
  • 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 2 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 supportive of a multi-hop model of GEM cycling, characterised by multiple surface depositions and re-emissions, in addition to long-range transport through the atmosphere.

Short summary
Mercury, a toxic metal, can be transported globally through the atmosphere, with deposition to ecosystems an important pathway to human exposure. 2 years of atmospheric mercury monitoring in tropical Australia supports recent evidence that Southern Hemisphere concentrations are lower than previously thought. Exchange between the atmosphere and ecosystems can take place on daily scales, with night deposition offset by morning re-emission. This could be an important transport pathway for mercury.
Final-revised paper