Collaborative Research: Verification of Atmospheric Mercury Redox Rates

The cross-institutional collaborative investigators in this project will provide a new comprehensive dataset of compounds involved in the oxidation of mercury in the atmosphere by quantitatively measuring divalent mercury compounds, which are the more water-soluble forms of mercury. Mercury is emitted into the atmosphere in the elemental state, which undergoes various reactions with atmospheric oxidants into the divalent form, but there exist many uncertainties about which oxidant species and what rates these reactions occur. The primary objective of this project is to use these new measurements of speciated mercury, along with previous measurements, to quantitatively characterize both the speciation of mercury and the radical budget of sampled plumes in the Salt Lake City region nearby a magnesium mining facility (U.S. Magnesium). Two graduate students will be trained over the course of this project, and the project team plans on providing policy makers with updated information pertaining to mercury chemistry and the impacts on human health. The team also has plans to engage with state regulators to potentially extend the societal benefits of the knowledge gained. A recent discovery pertaining to standard measurement techniques has revealed a systematic low bias that affects nearly all previous measurements of divalent mercury. The dual-channel continuous mercury measurement system developed, tested, and previously deployed by this research group can make divalent mercury measurements without this low bias. The work has three specific aims: (1) to conduct a year-long measurement campaign of elemental and divalent mercury, related oxidants, and other chemical and meteorological variables; (2) use the zero-dimensional F0AM model to identify which mercury chemical mechanisms and reaction rates minimize model-measurement discrepancies; and (3) update GEOS-Chem’s mercury oxidation mechanism with the F0AM parameters to minimize GEOS-Chem model-measurement discrepancies. Results from this work will enhance our understanding of mercury chemistry and chemical species affected by mercury chemistry, including halogens, ozone, and nitrogen oxides. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.