Interactions between Organic Oxidation and Acid-base Chemistry during Particle Formation and Growth

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This project involves the investigation of the formation and growth of new particles in the atmosphere. The effort includes the design and participation of experiments as part of the Cosmics Leaving Outdoor Droplets (CLOUD) consortium at CERN and participation in complementary experiments at Carnegie Mellon University (CMU). By improving the understanding of mechanisms for new particle formation, this project addresses vital national and international interests associated with climate change and air quality.This effort will study new particle formation involving nitric acid, sulfuric acid, ammonia, and amines, and particle formation by highly oxygenated organic compounds from both terpene and aromatic precursors. Experiments seek to answer the following questions: (1) How do the temperature dependencies of autoxidation as well as peroxy-radical ‘dimerization’ reactions across different systems (i.e., α pinene−RO2 + isoprene−RO2 → ROOR+O2) combine to control particle formation and growth in “pure organic” systems? (2) Do oxidized-organic and acid-base systems interact synergistically or independently during particle formation and growth, or can they even ‘spoil’ each other and inhibit nucleation? The two interconnected projects will focus on the interactions between acids, bases, and highly oxidized (and polar) organics ranging from particle formation itself to growth up to 5-10 nm. Key issues are to determine when nitric acid participates directly in particle formation versus activating growth of formed particles, and whether the acid-base and organic particle formation pathways proceed independently in the atmosphere or interact, either synergistically or antagonistically. Observables including measured formation and growth rates, gas-phase vapor measurements, and particle composition will combine to tightly constrain these coupled systems. 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).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.