Particle‐Phase Uptake and Chemistry of Highly Oxygenated Organic Molecules (HOMs) From <i>α</i>‐Pinene OH Oxidation
Laurent Poulain, Andreas Tilgner, Martin Brüggemann, Peter Mettke, Lin He, Janine Anders, Olaf Böge, Anke Mutzel, Hartmut Herrmann
Abstract
Abstract Secondary organic aerosol (SOA) forms a major part of the tropospheric submicron particle mass. Still, the exact formation mechanisms of SOA have remained elusive. It is now admitted that highly oxygenated organic molecules (HOMs) can contribute to a large fraction of SOA formation. In this study, we performed a set of chamber experiments to investigate the SOA formation, and the HOMs uptake and processing directly formed by OH‐radical initiated oxidation of α ‐pinene under two different aerosol seed conditions. Numerous HOM compounds were identified using advanced online and offline analytical techniques, and grouped into four classes according to their different uptake behaviors. For the first time, individual HOMs uptake coefficients ranging from 1.1 × 10 −2 to 1.5 × 10 −1 were experimentally determined and analyzed using a resistance model which considers uptake limitations by individual gas‐ and/or particle‐phase processes. This study demonstrates that the uptake coefficients of HOMs strongly depend on their molar mass and their respective O/C ratio. Results show that aerosol seed composition and phase state affect the initial uptake of HOMs. Furthermore, the study demonstrates that the acidity and/or different seed phase‐state can significantly enhance the subsequent uptake through occurring acidity‐driven reactions reflected in a reactive behavior, particularly under (NH 4 )HSO 4 seed conditions, promoting up to 3 times a higher SOA mass formation including the formation of highly oxidized organosulfates (HOOS). Overall, the present study implies that HOMs and their subsequent chemical processing can play an important role in both the early growth of newly formed particles and SOA formation when particle acidity is high.