Understanding atmospheric Hg redox transformations from novel Field observations and 3D atmospheric Hg models

Alkuin Koenig

Atmospheric oxidation of the dominant emitted Hg(0) form is a key process whereby Hg from natural and anthropogenic sources is converted to more soluble and reactive Hg(II) species that will be deposited to ecosystems. Recent theoretical, field and experimental studies have proposed new atmospheric Hg redox pathways, including alternative oxidants, and direct photoreduction of Hg(II) forms. These new pathways need to be integrated in atmospheric Hg models and tested against observations of atmospheric Hg and oxidant dynamics. Objectives : To improve understanding of atmospheric Hg observations including the role of key oxidants, photoreduction and reemissions.

Methodology & Expected Results : This project relies on previously made Hg observations, and on state of the art atmosphericHg models. The spatial and temporal variability of Hg(0) and Hg(II) species concentrations along with some oxidants (BrO, NOx, O3) will be investigated in regions where high oxidation rates are observed or suspected (polar regions, high altitude sites, tropical regions). An improved understanding of Hg(0) re-emission sources (snow, sea-ice, ocean, land) and their role in the atmospheric Hg budget will be proposed using available 1D and 3D atmospheric models. Improvement of reactions schemes and parametrization of Hg(0)oxidation and Hg(II) reduction using the latest version of the models (i.e. GEOSChem 3D) will be tested in high oxidation environments, using recent UGA/CNRS data and GMOS, AMNET data.

This thesis is part of GMOS-train project.
Supervisors : A. DOMMERGUE (CHIANTI) and J. SONKE (GET, Toulouse)