Laboratory studies of sulfate aerosols at upper tropospheric and lower stratospheric temperatures and compositions

Sulfate aerosols are abundant throughout the upper troposphere and lower stratosphere. These aerosols can affect the Earth's radiation balance, play a role in heterogeneous chemistry, and act as nuclei for cirrus cloud and polar stratospheric cloud formation. Recent studies have shown that tropospheric sulfate aerosols commonly contain 50% or more by mass organic species. In addition, chemical elements characteristic of earth minerals and meteorites are present within tropospheric and stratospheric sulfate particles. This thesis explores the influence of these materials on the chemical and physical properties of sulfate aerosols and therefore, the mechanisms by which cirrus clouds and polar stratospheric clouds form.; Hygroscopic growth curves were determined for pure dicarboxylic acids and eutonic mixtures of ammonium sulfate/dicarboxylic acids at 25°C. For the systems studied, we find that the presence of soluble dicarboxylic acids at the eutonic proportion depresses hygroscopic growth when compared to pure ammonium sulfate. In addition, we find that the presence of low solubility dicarboxylic acids at the eutonic proportion has no effect on the hygroscopic growth when compared to pure ammonium sulfate.; Ice nucleation temperatures were determined for aerosols composed of eutonic mixtures of ammonium sulfate/dicarboxylic acids. We find that the freezing temperatures of each mixed system were identical, for a given water activity of the solution, even though the solutions contained varying fractions of inorganic and organic components. Further experiments showed that the freezing behavior of pure dicarboxylic acid particles was identical to that of the other systems studied if the water activity was identical.; Finally, we have determined the total equilibrium metal solubility of iron and magnesium in 20--90 wt % H2SO4 solutions over the temperature range 200--300 K. We estimate that soluble Fe 2+ and Mg2+ comprise ∼0.02--0.27 wt % and ∼0.02--0.32 wt % respectively, of the H2SO4/H2O/{lcub}Fe 2+, Mg2+{rcub} solutions at temperatures and acid compositions representative of the atmosphere. Bulk freezing experiments were carried out on H2SO4 solutions containing appropriate amounts of dissolved metal. It was found that some solutions containing soluble metal froze ∼12--20 K higher than solutions containing no soluble metal.