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Abstract Title: Evidence Against Rapid Mercury Oxidation in Photochemical Smog
Presenter Name: Seth Lyman
Company/Institution: Bingham Research Center, Utah State University, Vernal, Utah, USA
Session: Special Session - New developments in understanding reactive mercury concentrations and chemistry
Co-Authors: Seth Lyman,Tyler Elgiar,Mae Gustin,Sarrah Dunham-Cheatham,Liji David,Lei Zhang

Abstract Information :

Mercury pollution is primarily emitted to the atmosphere, and atmospheric transport and chemical processes determine its fate in the environment, but scientific understanding of atmospheric mercury chemistry is clouded in uncertainty. Mercury oxidation by atomic bromine in the Arctic and the upper atmosphere is well established, but less is understood about oxidation pathways in conditions of anthropogenic photochemical smog. Many have observed rapid increases in oxidized mercury under polluted conditions, but it has not been clearly demonstrated that these increases are the result of local mercury oxidation. We measured elemental and oxidized mercury in an area that experienced abundant photochemical activity (ozone > 100 ppb) during winter inversion conditions that restricted entrainment of air from the oxidized mercury-rich upper atmosphere. Under these conditions, oxidized mercury concentrations decreased day-upon-day, even as ozone and other pollutants increased dramatically. A box model that incorporated rapid kinetics for reactions of elemental mercury with ozone and OH radical overestimated observed oxidized mercury, while incorporation of slower, more widely accepted reaction rates did not. Ambient measurements during this period were in line with output from a GEOS-Chem simulation that included regional chemistry and transport but did not capture local photochemistry. Our results show that rapid gas-phase mercury oxidation by ozone and OH in photochemical smog is unlikely.

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