Environmental Chamber Characterization for Quantifying Atmospheric Oxidants in Mercury Oxidation Mechanisms 
Alexis Harper1, Jaron Hansen1, Colleen Jones2, Seth Lyman2, Mae Gustin3, Sarrah Dunham-Cheatham4, Jessica Haskins5, Jackson Coley5, Ryan Thalman6, Trevor O'Neil2, Lizzy Lowe1, Dallin Giauque1, and KarLee Zager2
1 Brigham Young University, Provo, UT, 2 Bingham Research Center, Utah State University, Vernal, UT, 3 University of Nevada - Reno, Department of Natural Resources and Environmental Science, Reno, NV, 4 University of Nevada - Reno, Core Analytical Laboratory, Reno, NV, 5 University of Utah, Department of Atmospheric Science, Salt Lake City, UT, 6 Snow College, Natural Science and Mathematics, Chemistry, Ephraim, UT
Elemental mercury (Hg0) is the predominant form of mercury in the atmosphere. Although relatively inert and not immediately toxic, its long atmospheric lifetime enables global transport. Once oxidized to more reactive species, HgI and HgII, mercury becomes more water-soluble and readily deposits onto surfaces, where it can enter ecosystems and convert into compounds such as methylmercury, which are highly toxic and bioaccumulative. These transformations pose serious risks to human and ecological health.
Computational studies have identified hydroxyl radicals (OH), ozone (O3), and halogen species, particularly bromine (Br), as key oxidants driving atmospheric mercury oxidation. However, direct experimental validation under controlled conditions remains limited.
To address this gap, we constructed a 35 m3 polytetrafluoroethylene (PTFE) environmental chamber equipped with 200 UV-B and UV-C lamps to simulate atmospheric conditions. The chamber's large volume and optimized volume-to-surface-area ratio minimize wall-reaction artifacts that have complicated prior mercury kinetics studies. Prior to experimentation, characterization of the chamber, including flow rates, wall losses, and testing the UV irradiation system were completed. Elemental and oxidized mercury were measured using a dual channel Tekran system and a modified Reactive Mercury Active System (RMAS). Selected oxidants were measured according to their absorbance in different Broadband Cavity-Enhanced Absorbance Spectrometers (BBCEAS).
Currently, elemental mercury and selected oxidants are systematically being introduced into the chamber to investigate their individual and combined contributions to mercury oxidation. Promising preliminary results show that nitrous oxide (NO) can contribute to oxidizing Hg, even in dark conditions without photolysis, which was not previously predicted in computational models. While data has been collected on NO as a contributor to mercury oxidation, future studies will include introducing other chemical species, such as HONO, ozone, and bromine, to assess the effects of other oxidants in this larger atmospheric mechanism. By quantifying oxidation rates under controlled conditions, mechanistic understanding of atmospheric mercury transformation pathways will improve, thereby refining global models of mercury cycling and deposition.