Evidence for Interhemispheric Mercury Exchange in the Pacific Ocean Upper Troposphere

Alkuin M. Koenig, Jeroen E. Sonke, Olivier Magand, Marcos Andrade, Isabel Moreno, Fernando Velarde, Ricardo Forno, René Gutierrez, Luis Blacutt, Paolo Laj, Patrick Ginot, Johannes Bieser, Andreas Zahn, Franz Slemr, Aurélien Dommergue

Research output: Contribution to journalArticlepeer-review

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.

Original languageEnglish
Article numbere2021JD036283
JournalJournal of Geophysical Research D: Atmospheres
Volume127
Issue number10
DOIs
StatePublished - 27 May 2022

Bibliographical note

Funding Information:
The authors acknowledge the contribution of Ralf Ebinghaus to CARIBIC data. The authors thank Jennie Thomas and Diego Aliaga for scientific discussions and constructive comments on the manuscript. Financial support was granted through fundings from Institut Universitaire de France, LabEX OSUG@2020, LEFE CNRS/INSU, SNO CLAP as well as by ACTRIS‐France National Research infrastructure. The authors thank IRD (Institut de Recherche pour le Développement) and LFA for their logistical support during the field campaign. CHC TGM data were collected via instruments coordinated by the IGE‐PTICHA technical platform dedicated to atmospheric chemistry field instrumentation. The L1 Chacaltaya GMOS–Fr database is maintained by the French national center for Atmospheric data and services AERIS. This study was supported by the UMSA (Universidad Mayor de San Andrés) through the Laboratory for Atmospheric Physics (LFA) of the Institute for Physics Research. The LFA provided scientific, administrative, and logistical support. IAGOS‐CARIBIC data were created with support from the European Commission, national agencies in Germany (BMBF), France (MESR), and the UK (NERC), and the IAGOS member institutions ( http://www.iagos.org/partners ). This publication is part of the GMOS‐Train project that has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska‐Curie grant agreement No. 860497.

Funding Information:
The authors acknowledge the contribution of Ralf Ebinghaus to CARIBIC data. The authors thank Jennie Thomas and Diego Aliaga for scientific discussions and constructive comments on the manuscript. Financial support was granted through fundings from Institut Universitaire de France, LabEX OSUG@2020, LEFE CNRS/INSU, SNO CLAP as well as by ACTRIS-France National Research infrastructure. The authors thank IRD (Institut de Recherche pour le Développement) and LFA for their logistical support during the field campaign. CHC TGM data were collected via instruments coordinated by the IGE-PTICHA technical platform dedicated to atmospheric chemistry field instrumentation. The L1 Chacaltaya GMOS–Fr database is maintained by the French national center for Atmospheric data and services AERIS. This study was supported by the UMSA (Universidad Mayor de San Andrés) through the Laboratory for Atmospheric Physics (LFA) of the Institute for Physics Research. The LFA provided scientific, administrative, and logistical support. IAGOS-CARIBIC data were created with support from the European Commission, national agencies in Germany (BMBF), France (MESR), and the UK (NERC), and the IAGOS member institutions (http://www.iagos.org/partners). This publication is part of the GMOS-Train project that has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No. 860497.

Publisher Copyright:
© 2022. The Authors.

Keywords

  • interhemispheric exchange
  • interhemispheric gradient
  • mercury
  • model validation
  • pollutant transport

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