Faculty Research


Solubility and Freezing Effects of Fe2+ and Mg2+ in H2SO4 Solutions at Upper Tropospheric and Lower Stratospheric Temperatures and Compositions

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Chemical elements characteristic of earth minerals and meteorites are present within background tropospheric and stratospheric sulfate aerosol particles. However, it is unknown (a) if these elements are present predominately in a solid matrix, or rather as soluble aqueous metal ions or complexes and (b) how these impurities could affect particle freezing. To address these questions, we have determined the total equilibrium metal solubility (viz. [Fe$^{2 }$] $_{T}$ and [Mg$^{2 }$]$_{T}$ ) of MgSO$_{4}$, FeSO$_{4}$ 7H$_{2}$O, and a mixture of metal sulfates representative of meteorite samples in 20 - 90 wt % sulfuric acid solutions over the temperature range 200 - 300 K. We estimate that soluble Fe$^{2 }$ and Mg$^{2 }$ respectively comprise ca. 0.02 - 0.3 wt % of the solutions at temperatures and acid compositions representative of the atmosphere. Bulk freezing experiments were also carried out on sulfuric acid containing soluble metal. It was found that 57.6 wt % H$_{2}$SO$_{4}$ containing soluble meteoritic metal and 60 wt % H$_{2}$SO$_{4}$ containing soluble Fe and soluble meteoritic metal froze approximately 12 - 20 K higher than solutions containing no soluble metal.


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Wise, M. E., S.D. Brooks, R. M. Garland, D. J. Cziczo, D. M. Murphy, S. T. Martin, and M. A. Tolbert, Solubility and freezing effects of Fe2+ and Mg2+ in H2SO4 solutions at upper tropospheric and lower stratospheric temperatures and compositions, 2002 American Geophysical Union Meeting, San Francisco, CA, December 2002. Presentation A71F-08.