Research Interests

I am interested in understanding the chemistry and physics of particles in the atmosphere. These particles may influence atmospheric chemistry and climate not only on the present day Earth, but also on the planets and throughout Earth's history from the dawn of time. Our initial studies focused on measuring heterogeneous reactions on ice and nitric acid/ice surfaces representative of polar stratospheric clouds. We found that these icy clouds catalyzed reactions that convert inert chlorine compounds into more active forms capable of destroying stratospheric ozone. We now recognize that such reactions are an important step in the mechanism for formation of the yearly Antarctic "ozone hole." We have also studied heterogeneous reactions on sulfuric acid surfaces to probe the role of volcanic aerosols in global ozone depletion. In addition to measuring heterogeneous reactions, we have probed the nucleation and ultimate composition of the polar stratospheric cloud particles. Knowledge of cloud formation processes will ultimately help predict future cloud abundances and ozone levels in an environment where chlorine compounds are decreasing due to world-wide regulation, but polar stratospheric clouds may be increasing due to declining stratospheric temperatures because of climate change. Our current work emphasizes the role of chemically complex tropospheric aerosols in regulating current and future climate. We probe how particles with mixed compositions nucleate and grow to sizes where they impact visibility and radiation directly, and perhaps indirectly by modifying clouds. In addition, we are investigating the properties of particles that might have been present early in Earth's history to help constrain the climate and atmospheric chemistry under which early life on Earth developed. We are also studying the properties of particles on Mars and Titan (a moon of Saturn), which may be parallels to particles on Earth now and in the distant past.

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Section 16: Geophysics