Modeling Study of Elemental Mercury Depletion during Plume Episodes in Ohio River Valley

M. Kim, K. Crist, A. Kadakia, and K. John (USA)


Two phase box modeling, mercury chemistry, oxidation, reduction, Ohio River Valley


Located in the heart of the Ohio River Valley Region, Athens is affected by a wide variety of anthropogenic point-sources, which affect the observed mercury concentrations. A high variability in the RGM concentration has been observed at the Athens supersite, which leads to a variety of distinct mercury “episodes”. Many of the episodes can be attributed to nearby point sources including coal-fired power plants. Other episodes may occur due to meteorological stagnation, inversions, or the advection of an air mass with poor air quality. Athens, Ohio, episodes are most numerous in the spring, late summer, and early fall. Whereas some of the episodes feature a sudden and drastic elemental mercury increase, others display a significant loss of background elemental mercury within or just prior to the event. This Hg0 decrease was observed with simultaneous increase of RGM during the night time. This paper more closely examines the episodic nature of mercury depletion events at the Athens site, in terms of chemical transformation. A two phase box model was employed to simulate these episodes and to evaluate chemical transformation of mercury during the plume episodes. The box modeling results indicated that Hg0 decrease was attributed to oxidation by Cl2 and O3.

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