Anthropogenic mercury emissions are transported through the atmosphere as gaseous elemental mercury (Hg(0)) before they are deposited to Earth’s surface. Strong seasonality in atmospheric Hg(0) concentrations in the Northern Hemisphere has been explained by two factors: anthropogenic Hg(0) emissions are thought to peak in winter due to higher energy consumption, and atmospheric oxidation rates of Hg(0) are faster in summer. Oxidation-driven Hg(0) seasonality should be equally pronounced in the Southern Hemisphere, which is inconsistent with observations of constant year-round Hg(0) levels. Here, we assess the role of Hg(0) uptake by vegetation as an alternative mechanism for driving Hg(0) seasonality. We find that at terrestrial sites in the Northern Hemisphere, Hg(0) co-varies with CO2, which is known to exhibit a minimum in summer when CO2 is assimilated by vegetation. The amplitude of seasonal oscillations in the atmospheric Hg(0) concentration increases with latitude and is larger at inland terrestrial sites than coastal sites. Using satellite data, we find that the photosynthetic activity of vegetation correlates with Hg(0) levels at individual sites and across continents. We suggest that terrestrial vegetation acts as a global Hg(0) pump, which can contribute to seasonal variations of atmospheric Hg(0), and that decreasing Hg(0) levels in the Northern Hemisphere over the past 20 years can be partly attributed to increased terrestrial net primary production.

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We thank those involved in the EMEP efforts and those who have contributed by operating sites, performing chemical analysis and submitting data to the EBAS database. EMEP is funded through national contributions. We gratefully acknowledge the Air Quality Research Division of Environment Canada for the total gaseous mercury data, and the Earth System Research Laboratory at the National Oceanic and Atmospheric Administration and World Data Center for Greenhouse Gases for the CO2 data. This work contributed to the European Union 7th Framework Programme project Global Mercury Observation System. Logistical and financial support was provided by the French Polar Institute Paul-Emile Victor (Program 1028, GMOstral). This work was also funded by H2020 Marie Sklodowska-Curie grant agreement 657195 and Swiss National Science Foundation grant PZ00P2_174101 to M.J., and European Research Council grant ERC-2010-StG_20091028 to J.E.S.

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  1. Géosciences Environnement Toulouse, Centre National de la Recherche Scientifique/lnstitut de Recherche pour le Développement/Université de Toulouse, Toulouse, France

    • Martin Jiskra
    •  & Jeroen E. Sonke
  2. Environmental Geosciences, University of Basel, Basel, Switzerland

    • Martin Jiskra
  3. Department of Environmental, Earth, and Atmospheric Sciences, University of Massachusetts, Lowell, MA, USA

    • Daniel Obrist
  4. Institute of Coastal Research, Helmholtz Zentrum Geesthacht, Geesthacht, Germany

    • Johannes Bieser
    •  & Ralf Ebinghaus
  5. Norwegian Institute for Air Research, Kjeller, Norway

    • Cathrine Lund Myhre
    •  & Katrine Aspmo Pfaffhuber
  6. Swedish Environmental Research Institute, Gothenburg, Sweden

    • Ingvar Wängberg
  7. Atmospheric Composition Research Unit, Finnish Meteorological Institute, Helsinki, Finland

    • Katriina Kyllönen
  8. Climate Research Division, Environment and Climate Change Canada, Toronto, Canada

    • Doug Worthy
  9. Cape Point Global Atmosphere Watch Station, South African Weather Service, Stellenbosch, South Africa

    • Lynwill G. Martin
    • , Casper Labuschagne
    •  & Thumeka Mkololo
  10. Laboratoire des Sciences du Climat et de l’Environnement, Institut Pierre Simon Laplace (Commissariat à l’Énergie Atomique et aux Énergies Alternatives-Centre Nationnal de la Recherche Scientifique-Université de Versailles Saint-Quentin-en-Yvelines), Université Paris-Saclay, Gif Sur Yvette, France

    • Michel Ramonet
  11. Institut des Géosciences de l’Environnement, Université Grenoble Alpes/Centre National de la Recherche Scientifique/lnstitut de Recherche pour le Développement, Grenoble, France

    • Olivier Magand
    •  & Aurélien Dommergue


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M.J. initiated the project, performed the data analysis and wrote the manuscript together with J.E.S. and contributions from D.O., J.B. and A.D. J.B., R.E., C.L.M., K.A.P., I.W., K.K., D.W., L.G.M., C.L., T.M., M.R., O.M. and A.D. provided data. All authors read and commented on the manuscript.

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The authors declare no competing interests.

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Correspondence to Martin Jiskra.

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