Analytical Chemistry Seminar: Margaret Tolbert and Paul Ziemann
A new mechanism for solid formation in the atmosphere: Contact efflorescence
by Margaret Tolbert
The phase state of atmospheric particulate is an important factor in the magnitude of both the direct and indirect radiative effect of aerosols on climate. While the homogeneous phase transitions of deliquescence and efflorescence have been studied for decades, there is far less information available on heterogeneous efflorescence. Here we describe a new mechanism of possible atmospheric importance, contact efflorescence, a process that occurs when a supersaturated droplet comes in physical contact with a solid particle. A newly constructed optical trap is used to measure contact efflorescence for single levitated droplets exposed to single collisions. This talk will describe the experimental technique and present preliminary data for contact efflorescence.
Laboratory Studies of the Chemistry of Secondary Organic Aerosol Formation
by Paul Ziemann
In this talk I will describe for incoming graduate students the atmospheric chemistry research being conducted in my laboratory. Laboratory studies provide much of the fundamental data on reaction kinetics, products, and mechanisms that are needed to achieve a deep understanding of atmospheric chemistry and to develop detailed and accurate models that are used to establish air quality regulations and to predict the effects of human activities on global climate. Research in my laboratory focuses on the atmospheric chemistry of organic compounds emitted from natural and anthropogenic sources and the physical and chemical processes by which oxidized organic reaction products form microscopic aerosol particles. Studies are conducted in large-volume environmental chambers where experiments are designed to simulate but simplify atmospheric chemistry and conditions in order to obtain information on gas and particle chemical composition; gas and heterogeneous/multiphase reaction rates and equilibria; thermodynamic, hygroscopic, and phase properties of particles; and gas-particle-wall interactions. Obtaining such data is a challenge, but in this talk I will describe how we approach this problem by using a diverse array of measurement techniques including real-time and offline mass spectrometry, temperature-programmed thermal desorption, gas and liquid chromatography, NMR, spectrophotometry, and scanning mobility particle sizing. I will then provide examples of our use of these methods to develop quantitative chemical reaction mechanisms of organic gas and aerosol chemistry and models of SOA formation and particle properties such as hygroscopicity and describe some ongoing research projects.
Jointly sponsored by the Department of Chemistry and Biochemistry, CIRES, and the Environmental Program