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https://doi.org/10.5194/acp-2020-988
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-988
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  28 Oct 2020

28 Oct 2020

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This preprint is currently under review for the journal ACP.

Seasonal patterns of atmospheric mercury in tropical South America as inferred by a TGM continuous record at the Chacaltaya Station (5240 m) in Bolivia

Alkuin Maximilian Koenig1, Olivier Magand1, Paolo Laj1, Marcos Andrade2,7, Isabel Moreno2, Fernando Velarde2, Grover Salvatierra2, René Gutierrez2, Luis Blacutt2, Diego Aliaga3, Thomas Reichler4, Karine Sellegri5, Olivier Laurent6, Michel Ramonet6, and Aurélien Dommergue1 Alkuin Maximilian Koenig et al.
  • 1Institut des Géosciences de l'Environnement, Université Grenoble Alpes, CNRS, IRD, Grenoble INP, Grenoble, France
  • 2Laboratorio de Física de la Atmósfera, Instituto de Investigaciones Físicas, Universidad Mayor de San Andrés, La Paz, Bolivia
  • 3Institute for Atmospheric and Earth System Research/Physics, Faculty of Science, University of Helsinki, Helsinki, 00014, Finland
  • 4Department of Atmospheric Sciences, University of Utah, Salt Lake City, 84112, USA
  • 5Université Clermont Auvergne, CNRS, Laboratoire de Météorologie Physique, UMR 6016, Clermont-Ferrand, France
  • 6Laboratoire des Sciences du Climat et de l'Environnement, LSCE-IPSL (CEA-CNRS-UVSQ), Université Paris-Saclay, 91191 Gif-sur-Yvette, France
  • 7Department of Atmospheric and Oceanic Sciences, University of Maryland, College Park, MD, USA

Abstract. High-quality data of atmospheric mercury (Hg) is rare for South America, especially for its tropical part. In consequence, mercury dynamics are still highly uncertain in this region, a significant deficiency, as South America appears to play a major role in the global budget of this toxic pollutant. To address this issue, we performed nearly two years (July 2014–February 2016) of continuous high resolution total gaseous mercury (TGM) measurements at the Chacaltaya (CHC) mountain site in the Bolivian Andes, which is subject to a diverse mix of air masses coming predominantly from the Altiplano and the Amazon rainforest. For the first eleven months of measurements, we obtained a mean TGM concentration of 0.89±0.01 ng m−3, in good agreement with the sparse amount of data available from the continent. For the remaining nine months, we obtained a significantly higher TGM concentration of 1.34±0.01 ng m−3, a difference which we tentatively attribute to the strong El Niño event of 2015–2016. Based on HYSPLIT back-trajectories and clustering techniques, we show that lower mean TGM concentrations were linked to either westerly Altiplanic air masses or those originating from the lowlands to the south-east of CHC. Elevated TGM concentrations were related to northerly air masses of Amazonian or southerly air masses of Altiplanic origin, the former possibly linked to artisanal and small scale gold mining (ASGM), while the latter might be explained by volcanic activity. We observed a marked seasonal pattern, with low TGM concentrations in the dry season (austral winter), rising concentrations during biomass burning (BB) season, and highest concentrations at the beginning of the wet season (austral summer). With the help of simultaneously sampled equivalent black carbon (eBC) and carbon monoxide (CO) data, we use the clearly BB influenced signal during BB season (August to October) to derive a mean TGM/CO emission ratio of (2.3±0.6)·10−7 ppbvTGM ppbvCO−1, which could be used to constrain South American BB emissions. Through the link with in-situ measured CO2 and remotely sensed solar-induced fluorescence (SIF) as proxies for vegetation activity, we detect signs of a vegetation sink effect in Amazonian air masses and derive a best guess TGM/CO2 uptake ratio of 0.058±0.017 (ng m−3)TGM ppmCO2−1. Finally, significantly higher Hg concentrations in western Altiplanic air masses during the wet season as compared to the dry season point towards the modulation of atmospheric Hg by the Eastern Pacific Ocean.

Alkuin Maximilian Koenig et al.

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Alkuin Maximilian Koenig et al.

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Short summary
The environmental cycling of atmospheric mercury, a harmful global contaminant, is still not sufficiently constrained, partly due to missing data in remote regions. Here, we address this issue by presenting 20 months of atmospheric mercury measurements, sampled in the Bolivian Andes. We observe a significant seasonal pattern, whose key features we explore. Moreover, we deduce ratios to constrain South American biomass burning mercury emissions and the mercury uptake by the Amazon rainforest.
The environmental cycling of atmospheric mercury, a harmful global contaminant, is still not...
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