AGS-PRF: Hygroscopicity of Secondary Organic Aerosols Formed via Aqueous Reactions

Nakao, Shunsuke, Fort Collins CO

Investigators

Abstract

This project seeks better characterization of the climatic impact of a key atmospheric aerosol component, secondary organic aerosol (SOA), which contributes to both natural and anthropogenic aerosol concentrations. The focus is on the impacts of SOA on warm cloud formation. Current models, based on chamber experiments that focused on production of aerosols from gas-phase oxidation processes, tend to underpredict the mass concentrations and the extent of oxygenation of ambient organic aerosols. Growing evidence suggests that SOA formed in clouds or in hydrated haze particles via aqueous reactions (aqSOA) may reconcile these gaps: these aqueous reactions have been shown to proceed under atmospheric conditions in the laboratory, and reaction products are highly oxygenated. Although aqSOA hygroscopicity, a measure of a particle's ability to participate in cloud drop formation or cloud condensation nucleating (CCN) activity, is expected to be high due to its highly oxidized composition, few studies have confirmed this relationship to evaluate its climatic impact. This study will correlate CCN activity of aqSOA, component polarity, and composition for the first time. A new analytical method will be applied for determination of CCN activity of aqSOA as a function of component polarity, providing new insights on the unresolved contribution of many chemical species to overall hygroscopicity. Elemental analysis of aerosol data obtained using a high-resolution time-of-flight aerosol mass spectrometer will be used to evaluate how polarity and hygroscopicity relate to oxygen:carbon ratios in the aerosol phase. The work will be conducted at Colorado State University (CSU) under the mentorship of Prof. Sonia Kreidenweis. In terms of broader impacts, the results of this project will help improve the global budget of atmospheric organic aerosols and the representation of organic aerosol climate impacts. Also, the principal investigator will be actively involved in educational activities at CSU including serving as a discussion leader for a graduate level course on responsible conduct of research. The principal investigator will also be a research mentor to interns via the NSF-sponsored Center for Multiscale Modeling of Atmospheric Processes at CSU.