10th International Aerosol Conference
September 2 - September 7, 2018
America's Center Convention Complex
St. Louis, Missouri, USA

Abstract View


There's No Place Like HOM: Modeling Peroxy Radical Chemistry to Understand HOM Yields

MEREDITH SCHERVISH, Wayne Chuang, Neil Donahue, Carnegie Mellon University

     Abstract Number: 349
     Working Group: Aerosol Chemistry

Abstract
Knowledge of gas-phase oxidation chemistry is central to our understanding of aerosols. While gas-phase products of a wide range of volatilities are produced via oxidation of emitted precursors, low and extremely-low volatility gas-phase organic compounds are especially important because of their contribution to growth of particles as well as to the nucleation of new particles. Recent experimental work has shown the presence of highly oxidized molecules (HOMs), having vapor pressures in LVOC to ELVOC range, formed from the oxidation of alpha-pinene in both field and laboratory studies. These compounds are formed when peroxy radicals from the initial precursor oxidation "auto-oxidize" allowing them to rapidly undergo multi-generational oxidation chemistry. This process, involving a high energy barrier and thus being highly temperature-dependent, competes with radical termination reactions with NOx, HO2, and other RO2 radicals. Under different conditions, this competition results in vastly different stable products. Under low NOx and high temperature conditions, auto-oxidation dominates the fate of peroxy radicals leading to highly oxidized, low (and extremely low) volatility products including highly oxidized dimers. Under high NOx and/or low temperature conditions, radical termination reactions dominate leading to products that are less oxidized and have higher volatilities. This competition is crucial in our understanding of the formation of ELVOC dimers as the dimer formation reaction may be dependent on the ability of RO2 radicals to cluster together, requiring that they themselves have a low enough vapor pressure. This work seeks to underline the importance of the competition between auto-oxidation and radical termination under different conditions and explore HOM formation in chamber experiments through modeling.