(5cg) Atmospheric Chemistry at Environmental Interfaces

My research focuses on understanding the chemical and physical processes that occur at environmental interfaces, and how they influence the chemical balance of the atmosphere. Atmospheric aerosol and cloud particles ranging in size from ~3 nm to 50 microns significantly affect climate and provide dynamic catalytic surfaces or liquid media for the chemical processing of gas-phase species. Laboratory, field, and modeling studies have established that heterogeneous chemistry plays critical roles in polar ozone depletion in the stratosphere (the ?ozone hole?), in climate, and in regulating the oxidative capacity of the troposphere. Soil, water, snow, and ice at the Earth's surface can also be significant sources and sinks of tropospheric gas and particle phase species, and a quantitative understanding of these processes is necessary from both an atmospheric chemistry and a biogeochemistry perspective. However, gas-particle interactions, and interactions between the atmosphere and Earth's surface, continue to be major sources of uncertainty limiting our understanding of atmospheric chemistry.

Heterogeneous chemistry in the troposphere is not nearly as well-understood as stratospheric chemistry, in part because much uncertainty surrounds the chemical composition and physical state of tropospheric aerosols. Besides participating in heterogeneous chemistry, aerosol matter can be formed via oxidation of trace gases in the troposphere, resulting in a chemical feedback. Laboratory and field research is needed to eludicate the mechanisms of aerosol formation and heterogeneous reaction processes, as well as of the interactions between the atmosphere and the earth's surface. Their quantitative impact on atmospheric chemistry and climate can then be evaluated via implementation in global-scale Earth system models. Identifying heterogeneous and multiphase reactive systems key to the chemistry of the troposphere, probing them via appropriate model laboratory systems, and ultimately developing a theoretical framework for accurate representation of these processes in atmospheric chemistry and climate models all present unique challenges.

My research program will combine laboratory and modeling studies focused on understanding and quantifying the chemistry of heterogeneous and multiphase systems affecting Earth's atmosphere. The results of these studies will improve our understanding of the effects of human activity on our environment and provide insight into practical approaches for pollution mitigation. Examples of science questions that I plan to address include: 1)What are the sources of secondary organic material in atmospheric aerosols? 2)How does the interfacial chemistry of sea salt aerosols affect the budget of reactive halogen species in the atmosphere? 3)What is the extent of the interaction of trace gases with mineral dust aerosols? What opportunities exist for low-cost adsorption-based pollution mitigation technology? 4)How does the air-snow exchange of trace gases influence polar atmospheric chemistry and our understanding of past atmospheric chemistry and climate based on ice core records?

The analytical tools that will be used in my laboratory will be centered on a custom-built high-sensitivity chemical ionization mass spectrometer (CIMS) system. This powerful and extremely versatile technique can be used to detect many gas-phase species of atmospheric interest with high selectivity at detection limits on the order of 1 ppt. The use of a heated inlet with CIMS detection enables real-time measurements of laboratory aerosol composition simultaneously with gas-phase composition (Aerosol CIMS). Aerosol CIMS allows speciated measurements of organic aerosol components with high selectivity and high sensitivity. Chemical ionization results in low fragmentation, thus simplifying the identification and quantification of organic aerosol components. My work has demonstrated that on-line analysis of the gas-particle partitioning of semivolatiles to obtain heats of vaporization for individual aerosol components is possible via control of the vaporization temperature.