Mercury in the free troposphere and bidirectional atmosphere-vegetation exchanges - Insights from Maïdo mountain observatory in the Southern Hemisphere tropics
Koenig, Alkuin M.; Magand, Olivier; Verreyken, Bertet al.
2023 • In Atmospheric Chemistry and Physics, 23 (2), p. 1309 - 1328
[en] Atmospheric mercury (Hg) observations in the lower free troposphere (LFT) can give important insights into Hg redox chemistry and can help constrain Hg background concentrations on a regional level. Relatively continuous sampling of LFT air, inaccessible to most ground-based stations, can be achieved at high-altitude observatories. However, such high-altitude observatories are rare, especially in the Southern Hemisphere (SH), and atmospheric Hg in the SH LFT is unconstrained. To fill this gap, we continuously measured gaseous elemental mercury (GEM; hourly) and reactive mercury (RM; integrated over g1/4g6-14gd) for 9 months at Maïdo mountain observatory (2160gmga.s.l.) on remote Reunion Island (21.1g gS, 55.5g gE) in the tropical Indian Ocean. GEM exhibits a marked diurnal variation characterized by a midday peak (mean: 0.95gnggm-3; SD: 0.08gnggm-3) and a nighttime low (mean: 0.78gnggm-3; SD: 0.11gnggm-3). We find that this diurnal variation is likely driven by the interplay of important GEM photo-reemission from the islands' vegetated surfaces (i.e. vegetationg+gsoil) during daylight hours (8-22gnggm-2gh-1), boundary layer influences during the day, and predominant LFT influences at night. We estimate GEM in the LFT based on nighttime observations in particularly dry air masses and find a notable seasonal variation, with LFT GEM being lowest from December to March (mean 0.66gnggm-3; SD: 0.07gnggm-3) and highest from September to November (mean: 0.79gnggm-3; SD: 0.09gnggm-3). Such a clear GEM seasonality contrasts with the weak seasonal variation reported for the SH marine boundary layer but is in line with modeling results, highlighting the added value of continuous Hg observations in the LFT. Maïdo RM is 10.6gpggm-3 (SD: 5.9gpggm-3) on average, but RM in the cloud-free LFT might be about twice as high, as weekly-biweekly sampled RM observations are likely diluted by low-RM contributions from the boundary layer and clouds.
Disciplines :
Chemistry
Author, co-author :
Koenig, Alkuin M.; Institut des Geosciences de l'Environnement, Universite Grenoble Alpes, CNRS, INRAE, IRD, Grenoble, France
Magand, Olivier; Institut des Geosciences de l'Environnement, Universite Grenoble Alpes, CNRS, INRAE, IRD, Grenoble, France
Verreyken, Bert ; Université de Liège - ULiège > Département GxABT > Biosystems Dynamics and Exchanges (BIODYNE) ; Royal Belgian Institute for Space Aeronomy, BIRA-IASB, Brussels, Belgium ; Department of Chemistry, Ghent University, Ghent, Belgium ; Laboratoire de l'Atmosphère et des Cyclones, UMR 8105, CNRS, Universite de la Reunion, La Reunion, France ; NOAA Chemical Sciences Laboratory, Boulder, United States
Brioude, Jerome ; Laboratoire de l'Atmosphère et des Cyclones, UMR 8105, CNRS, Universite de la Reunion, La Reunion, France
Amelynck, Crist; Royal Belgian Institute for Space Aeronomy, BIRA-IASB, Brussels, Belgium ; Department of Chemistry, Ghent University, Ghent, Belgium
Schoon, Niels; Royal Belgian Institute for Space Aeronomy, BIRA-IASB, Brussels, Belgium
Colomb, Aurelie; Laboratoire de Meteorologie Physique, UMR6016, CNRS, Universite Clermont Auvergne, Aubière, France
Ferreira Araujo, Beatriz; Geosciences Environnement Toulouse, CNRS/IRD/Universite Paul Sabatier Toulouse 3, Toulouse, France
Ramonet, Michel ; Laboratoire des Sciences du Climat et de l'Environnement, Universite Paris-Saclay, CEA-CNRS-UVSQ, UMR8212, Gif-sur-Yvette, France
Sha, Mahesh K. ; Laboratoire des Sciences du Climat et de l'Environnement, Universite Paris-Saclay, CEA-CNRS-UVSQ, UMR8212, Gif-sur-Yvette, France
Cammas, Jean-Pierre; Observatoire des Sciences de l'Univers À la Reunion (OSU-R), UAR 3365, CNRS, Universite de la Reunion, La Reunion, France
Sonke, Jeroen E.; Geosciences Environnement Toulouse, CNRS/IRD/Universite Paul Sabatier Toulouse 3, Toulouse, France
Dommergue, Aurelien ; Institut des Geosciences de l'Environnement, Universite Grenoble Alpes, CNRS, INRAE, IRD, Grenoble, France
Mercury in the free troposphere and bidirectional atmosphere-vegetation exchanges - Insights from Maïdo mountain observatory in the Southern Hemisphere tropics
H2020 - 654109 - ACTRIS-2 - Aerosols, Clouds, and Trace gases Research InfraStructure
Funders :
EU - European Union [BE] BELSPO - Belgian Federal Science Policy Office [BE]
Funding text :
The PTR-MS data from BIRA-IASB were obtained in the framework of the OCTAVE project, funded by the Belgian Federal Science Policy Office (grant no. BR/175/A2/OCTAVE) with additional support for deploying the instrument at Maïdo from Horizon 2020 (ACTRIS-2, grant no. 654109).This publication is part of the GMOS-Train project that has received funding from the European Union's Horizon 2020 research and innovation programme under Marie Skłodowska-Curie grant agreement no. 860497.We thank OPAR (Observatoire de Physique de l'Atmosphère à La Réunion), funded by CNRS-INSU and Université de La Réunion and managed by OSU-R (Observatoire des Sciences de l'Univers à La Réunion, UMS 3365). Jean-Marc Metzger, from OSU-R, and Christelle Barthe, from LACy and Météo-France, are particularly thanked for their support in the implementation of OPAR's instrumentation and the provision of meteorological data.This research has been supported by Horizon 2020 in the framework of GMOS-Train (grant no. 860497) and ERA-PLANET (grant no. 689443), the Belgian Federal Science Policy Office (grant no. BR/175/A2/OCTAVE), and the French national LEFECHAT CNRS/INSU program (TOPMMODEL project, grant no. AO2017-984931 to Olivier Magand).
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