Chemical Engineering Seminar

Abstract: Particle nucleation can occur via chemical reactions in the new particle (usually acid-base proton transfer) or via volatility alone (preceded by gas-phase oxidation to form low volatility products). Here we focus on the second case, considering "pure" organic nucleaiton. In many cases this involves three steps. First, oxidation chemistry must (quickly) form highly functionalized products. This is often via "autoxidation" involving H-transfer isomerization of peroxy and alkoxy radicals. This chemistry slows dramatically as temperature drops. Second, association reactions between peroxy radicals can form large, ultra low volatility products. The kinetics of these reactions are varied and complex. Third, molecules need to form clusters that evaporate slowly enough for more molecules to condense to them before they evaporate, forming a particle. Here we will explore aspects of all three of these steps, using data from the CLOUD experiment at CERN on nucleation following oxidation of alpha-pinene over the full temperature range of the troposphere (223 K - 298 K), putting each in a theoretical, quantitative context.

Bio: I was born in Pittsburgh, and I live in Pittsburgh, but a lot happened in between. Somewhere along the line, I was given an AB in Physics from Brown University and then a PhD in Meteorology from MIT before taking the red line up to Harvard and becoming a kineticist under the watchful eye of Jim Anderson. After carefully avoiding aerosols for almost 20 years, I moved to Carnegie Mellon University to take up a faculty position and fell in with Spyros Pandis, Peter Adams, and Allen Robinson, and so unavoidably started to think about aerosols. However, I stuck to my guns about gas-phase chemistry and remain convinced (some might say biased) that gas-phase chemistry is overwhelmingly important for the number, size, composition, and other properties of atmospheric aerosols. I eventually joined the CLOUD collaboration at CERN, more or less returning to particle physics after a 30-year hiatus, where I continue to be fascinated by the connection between the gas phase and particle formation and growth.