Brandon Connelly
B.A., Chemistry and History, 1995

Uptake of organics by thin sulfuric acid/ammonium sulfate films: The kinetics of acid-catalyzed secondary organic formation

While the atmosphere is primarily composed of gas phase species, it is now recognized that liquid and solid aerosol particles have a strong impact on global climate and air quality. Tropospheric aerosols directly affect climate by scattering and absorbing radiation, and indirectly by serving as cloud condensation nuclei and ice nuclei. Changes to aerosol composition due to anthropogenic activities can alter our climate and air quality on a local and global scale. Because of the environmental and health concerns it is of the utmost importance to understand the physical and chemical mechanisms that underlie aerosol particle formation and composition.

Sulfates have been identified as an important component of tropospheric aerosol. Sulfuric acid in the atmosphere has natural and anthropogenic sources. A fraction of the sulfate aerosols are found in neutralized forms such as ammonium sulfate and bisulfate. However, a key finding in the last decade is that almost all tropospheric sulfate aerosols are internal mixtures of many components, with organics compromising 50% or more of the particle mass. The mechanisms by which the organics become incorporated into the sulfate particles are not clear. Recent studies suggest that acid catalyzed chemical reactions may play an important role in the uptake process. However, while previous work indicates that sulfuric acid does indeed catalyze organic reactions of atmospheric relevance, there is little kinetic data available.

In this proposal, I plan to carry out laboratory studies of organic uptake by sulfuric acid and ammonium sulfate to further our understanding of how organics become incorporated into aerosol particles. I propose kinetics studies of the uptake of several key organics by sulfates. This work will be performed as a function of temperature, relative humidity, and organic partial pressure. The kinetic measurements will enable a more accurate determination of the atmospheric relevance of acid catalyzed reactions on sulfuric acid. The work will thus help elucidate the role of acid catalyzed reactions as a source of secondary organic matter observed in atmospheric aerosols.

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