Exploring atmospheric mercury in tropical zone of the Southern Hemisphere

Laboratoire(s) de rattachement : IGE

Encadrant : DOMMERGUE Aurelien

Co-encadrant : MAGAND Olivier

Niveau de formation & pré-requis : Knowledge on atmospheric sciences may be necessary. Data processing (R, Python, Matlab), numerical model, motivation and creativity are expected skills.

Mots-clés : Chemistry, Mercury, Halogens, Environment, Meteorology, Modeling

With the signing of the UNEP Minamata Convention in 2013, governments have globally accepted that mercury (Hg) is toxic ; scientific needs will therefore shift towards best implementation practices of the Convention. With most Hg emissions emanating from the energy-industrial sector this means that governments have to balance economic and environmental interests. How does one assess that balance ? Biogeochemical Hg cycling is complex : superimposed on the strongly perturbed inorganic Hg cycle is the natural process of biomethylation that generates the bioaccumulating monomethyl-Hg form that we are all exposed to when we consume fish. Comprehensive 3D models of the biogeochemical Hg cycle that have been developed over the past 15 years can capture this complexity and evaluate the effectiveness of environmental policy scenarios.

Both natural and anthropogenic atmospheric Hg emissions are mostly in the form of inert gaseous elemental Hg(0) (Pacyna et al. 2010). The key atmospheric Hg transformation that shuttles emitted Hg(0) back to marine and continental ecosystems is oxidation, yet neither the oxidant, nor the identity and precise levels of oxidized forms of Hg(II), nor the dominant regions/altitudes where oxidation takes place are precisely known (Jaffe et al. 2014). In addition, current operational Hg(II) measurement techniques are under mounting criticism and thought to be inaccurate. This lack of knowledge hampers modern 3D global Hg models in predicting ecosystem Hg loads under future Hg emission scenarios (UNEP 2013).

Between September 2017 and July 2018, we have launched continuous measurements of gaseous elemental mercury (and other species) at the Maido Observatory of La Reunion (altitude around 2500m). This observatory is situated in the tropical zone of the Southern Hemisphere. The aim of this study are to : (i) study atmospheric oxidation of mercury at this latitude (using new halogen measurements and modeling studies), (ii) document our knowledge of the processes occurring at these latitude and altitude. Today, knowledge of the Southern Hemispheric cycle of Hg is particularly unknown. That’s why this is important to note that this is the first data set ever obtained in a tropical site of the SH. This will challenge and change our understanding of Hg chemistry, deposition and fate on a global scale.

The goal of this internship is to begin the exploration of the data that are collected. In particular, we will study the impact of local meteorology on the mercury record (vertical mixing, solar radiation, rain events), the different contribution of anthropogenic or natural (continental and oceanic) sources of mercury with the help of backtrajectories simulation (FLEXPART model). The data obtained at the Maido will be compared with data set that we currently have in Amsterdam Island (sea level) in the Indian Ocean. We may also try to use different models of atmospheric chemistry. Future work (potentiality Ph.D) will include work on oxidized species of mercury, Hg isotopes, and modeling.

Pour candidater : Adresser un CV et une lettre de motivation par email aux adresses ci-dessous
aurelien.dommergue univ-grenoble-alpes.fr
olivier.magand univ-grenoble-alpes.fr