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Journal Articles Journal of Geophysical Research: Atmospheres Year : 2022

Evidence for Interhemispheric Mercury Exchange in the Pacific Ocean Upper Troposphere

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Marcos Andrade
  • Function : Author
Isabel Moreno
  • Function : Author
Fernando Velarde
  • Function : Author
Ricardo Forno
  • Function : Author
René Gutierrez
  • Function : Author
Luis Blacutt
  • Function : Author
Patrick Ginot
  • Function : Author
Johannes Bieser
  • Function : Author
Andreas Zahn
  • Function : Author
Franz Slemr
  • Function : Author

Abstract

Even though anthropogenic mercury (Hg) emissions to the atmosphere are ∼2.5 times higher in the Northern Hemisphere (NH) than in the Southern Hemisphere (SH), atmospheric Hg concentrations in the NH are only ∼1.5 times higher than in the SH. Global Hg models attribute this apparent discrepancy to large SH oceanic Hg emissions or to interhemispheric exchange of Hg through the atmosphere. However, no observational data set exists to serve as a benchmark to validate whether these coarse-resolution models adequately represent the complex dynamics of interhemispheric Hg exchange. During the 2015-2016 El Niño, we observed at mount Chacaltaya in the tropical Andes a ∼50% increase in ambient Hg compared to the year before, coinciding with a shift in synoptic transport pathways. Using this event as a case study, we investigate the impact of interhemispheric exchange on atmospheric Hg in tropical South America. We use HYSPLIT to link Hg observations to long-range transport and find that the observed Hg increase relates strongly to air masses from the tropical Pacific upper troposphere (UT), a region directly impacted by interhemispheric exchange. Inclusion of the modeled seasonality of interhemispheric air mass exchange strengthens this relationship significantly. We estimate that interhemispheric exchange drives Hg seasonality in the SH tropical Pacific UT, with strongly enhanced Hg between July and October. We validate this seasonality with previously published aircraft Hg observations. Our results suggest that the transport of NH-influenced air masses to tropical South America via the Pacific UT occurs regularly but became more detectable at Chacaltaya in 2015-2016 because of a westward shift in air mass origin.
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Dates and versions

insu-03706371 , version 1 (28-06-2022)

Licence

Attribution - CC BY 4.0

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Alkuin M. Koenig, Jeroen E. Sonke, Olivier Magand, Marcos Andrade, Isabel Moreno, et al.. Evidence for Interhemispheric Mercury Exchange in the Pacific Ocean Upper Troposphere. Journal of Geophysical Research: Atmospheres, 2022, 127, ⟨10.1029/2021JD036283⟩. ⟨insu-03706371⟩
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