Understanding Formation of Condensible Organics from Photochemical Oxidation During New-Particle Formation Experiments

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This project focuses on the study of the formation and growth of new particles in the atmosphere. The research will combine collaborative experiments at CERN as part of the Cosmics Leaving OUtdoor Droplets (CLOUD) consortium, with smog-chamber studies at Carnegie Mellon University (CMU). The CLOUD experimental facility is likely the world's most sophisticated experiment addressing atmospheric new-particle formation. It was constructed to measure new particle formation under highly controlled, ultra-clean conditions.At CLOUD, the CMU team will use an iodide chemical ionization mass spectrometer to measure the composition of gases and growing particles, the later by thermal desorption from teflon filters (FIGAERO CIMS). The major objective will be to understand how gas-phase oxidation chemistry makes products with extraordinary low vapor pressures, capable of forming new particles and also condensing on existing particles making them grow. A major focus will be to compare chemical conditions in CLOUD, which more closely resemble the clean background atmosphere, with those in traditional smog chamber experiments, that often exceed those in the most polluted cities. The project will focus on the role of peroxy radical formation and subsequent "auto-oxidation" that can convert semi-volatile peroxy radicals into low-volatility peroxy radicals, and the subsequent termination chemistry that generates condensible products.This research will form the core of two student dissertations. One will focus principally on gas-phase oxidation chemistry, specifically the temperature dependent sources and fate of highly oxidized peroxy radicals that is hypothesized to be at the center of the formation of low-volatility and extremely low-volatility organic compounds. The other will focus on the composition of the condensed phase and the potential for reactive uptake of semivolatile organic compounds to contribute to particle growth. The project results will yield a much better understanding of the rate-limiting elementary steps associated with new-particle formation and growth and competing atmospheric processes that might interfere with those rate-limiting steps.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.