Seasonal patterns of atmospheric mercury in tropical South America as inferred by a continuous total gaseous mercury record at Chacaltaya station (5240m) in Bolivia

Alkuin Maximilian Koenig, Olivier Magand, Paolo Laj, Marcos Andrade, Isabel Moreno, Fernando Velarde, Grover Salvatierra, René Gutierrez, Luis Blacutt, Diego Aliaga, Thomas Reichler, Karine Sellegri, Olivier Laurent, Michel Ramonet, Aurélien Dommergue

Research output: Contribution to journalArticlepeer-review

4 Scopus citations

Abstract

High-quality atmospheric mercury (Hg) data are rare for South America, especially for its tropical region. As a consequence, mercury dynamics are still highly uncertain in this region. This is 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 2 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 11 months of measurements, we obtained a mean TGM concentration of 0.89±0.01 ng m-3, which is in good agreement with the sparse amount of data available from the continent. For the remaining 9 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 (Hybrid Single-Particle Lagrangian Integrated Trajectory) 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 southeast of CHC. Elevated TGM concentrations were related to northerly air masses of Amazonian or southerly air masses of Altiplanic origin, with the former possibly linked to artisanal and small-scale gold mining (ASGM), whereas 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 the biomass burning (BB) season, and the 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 the BB season (August to October) to derive a mean TGM/CO emission ratio of (2.3±0.6)×10-7 ppbvTGM ppbv-1 CO, which could be used to constrain South American BB emissions. Through the link with CO2 measured in situ and remotely sensed solarinduced 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 (ngm-3)TGM ppm-1 CO2. Finally, significantly higher Hg concentrations in western Altiplanic air masses during the wet season compared with the dry season point towards the modulation of atmospheric Hg by the eastern Pacific Ocean.

Original languageEnglish
Pages (from-to)3447-3472
Number of pages26
JournalAtmospheric Chemistry and Physics
Volume21
Issue number5
DOIs
StatePublished - 5 Mar 2021

Bibliographical note

Funding Information:
Acknowledgements. These observations contribute to the GEO GOS4M (Global Observation System for Mercury; http://www. gos4m.org, last access: 23 October 2020). It is aimed to support the UN Global Mercury Fate and Transport Research partnership (UN FandT) of the UN Environment in the implementation of the Minamata Convention (http://www.mercuryconvention.org, last access: 23 October 2020) by providing a knowledge platform on mercury in the environment and human health. It will support UN Environment and the United Nations to assess the effectiveness of measures that will be undertaken. CHC TGM data, accessible in GMOS-FR, have been collected through funding obtained by the European Union 7th Framework Programme project Global Mercury Observation System (GMOS 2010–2015), LabEX OSUG@2020 (ANR10 LABX56), LEFE CNRS/INSU (SAMOA program), SNO CLAP, as well as by ACTRIS-France National Research infrastructure. CHC TGM data were collected via instruments coordinated by the IGE-PTICHA technical platform dedicated to atmospheric chemistry field instrumentation. Moreover, we acknowledge the logistical and financial support from IRD (Institut de Recherche pour le Développement) and LFA during the field campaign in Bolivia. CO2 observations are obtained as part of the SNO IFA French monitoring network. We acknowledge the financial support provided by the PAPILA (Prediction of Air Pollution in Latin America and the Caribbean) mobility project. Analyses and visualizations used in this study were produced with the Giovanni online data system, which is developed and maintained by the NASA GES DISC.

Funding Information:
Financial support. This research has been supported by the EU

Publisher Copyright:
© 2021 EDP Sciences. All rights reserved.

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