Synergistic O ₃ + OH oxidation pathway to extremely low-volatility dimers revealed in β-pinene secondary organic aerosol

Abstract

Significance Secondary organic aerosol (SOA) is ubiquitous in the atmosphere and plays a pivotal role in climate, air quality, and health. Monoterpenes, emitted in large quantities from forested regions, are a dominant source of SOA globally, with dimers having been identified as key contributors to particle formation and growth. Here, we establish the role of concerted oxidation by O 3 and OH as a significant route to dimer formation in SOA generated from β-pinene, the second-most-abundant monoterpene emitted to the atmosphere. Production of this class of dimers is found to occur through both gas- and particle-phase processes. Dimer formation via synergistic O 3 + OH oxidation could represent an appreciable source of “missing” SOA not included in current atmospheric models.