Atmospheric deposition of metals emitted by anthropogenic activities has contributed metals to soils worldwide. A ferromanganese refinery, located in Marietta, OH, is currently the largest source of manganese (Mn) emitted into the atmosphere in the U.S.A. Particulate emissions during production are up to 35% manganese oxide (MnO2) by weight and are dominantly in the size range of 0.05 to 0.4 μm diameter. Particles of that size are both highly mobile and respirable. In order to understand how emissions of Mn and another emitted metal, Cr, has varied over the lifetime of the refinery, a series of soil cores were collected at sites located from 1 to 47 km from the refinery. Concentrations of soil-surface Mn and Cr are enriched 9 and 3 times that of the parent material within 1.2 km of the refinery, respectively. Total mass of Mn added to soils per unit land area integrated over the soil depth was calculated to be 77 mg Mn cm-2 near the refinery. The geographic extent of Mn deposition due to EMI as indicated by a positive integrated Mn mass flux value extends up to 25 km or possibly even beyond 47 km from EMI, depending on assumed composition of the parent material. Mn deposition rates were also simulated with an atmospheric dispersion model (SCIPUFF) using meteorological data from a local weather station and emission rates for the refinery, though the model under-predicted recent deposition. Soil-derived integrated mass flux values for Mn coupled with recent estimates of Mn deposition in Marietta suggest that deposition rates in the past may have been 3 orders of magnitude greater than today’s rates. Such a higher historic emission rate cannot be tested because no quantitative data are available for emissions earlier than 1988. However, higher emissions in the past are likely given the history of metal production. Decreases in deposition rates are also likely due to emission control technology installed as a response to regulations such as the Clean Air Act (1970): the soil measurements document that the Clean Air Act is the likely cause of more than 166x reduction in deposition per metric ton of Mn alloy used. These results document that soil measurements can help reconstruct past metal deposition rates. In fact, when developed on easily-identified parent material, soil profiles may be more useful indicators of the past behavior of metal-emitting sources over decadal time scales than atmospheric dispersion models.
Carter, Megan (2013): Exploring a 60-year record of manganese deposition in Marietta Ohio using soil chemistry and atmospheric dispersion modeling . Master of Science, Geosciences, The Pennsylvania State University, p. 114.
This Paper/Book acknowledges NSF CZO grant support.
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