Atmospheric Chemistry and Physics, vol. 10, issue 23 (2010) pp. 11753-11767
We present vapor pressure data of the C 2 to C 5 di-carboxylic acids deduced from measured evaporation rates of single levitated particles as both, aqueous droplets and solid crystals. The data of aqueous solution particles over a wide concentration range allow us to directly calculate ac-tivities of the dicarboxylic acids and comparison of these ac-tivities with parameterizations reported in the literature. The data of the pure liquid state acids, i.e. the dicarboxylic acids in their supercooled melt state, exhibit no even-odd alter-nation in vapor pressure, while the acids in the solid form do. This observation is consistent with the known solubilities of the acids and our measured vapor pressures of the super-cooled melt. Thus, the gas/particle partitioning of the differ-ent dicarboxylic acids in the atmosphere depends strongly on the physical state of the aerosol phase, the difference being largest for the even acids. Our results show also that, in general, measurements of vapor pressures of solid dicarboxylic acids may be com-promised by the presence of polymorphic forms, crystalline structures with a high defect number, and/or solvent inclu-sions in the solid material, yielding a higher vapor pressure than the one of the thermodynamically stable crystalline form at the same temperature.
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