Abstract View
Nucleation Dynamics and Fragmentation Reactions Explain Differences in Secondary Organic Aerosol Formation between Environmental Chambers and Oxidation Flow Reactors
CHARLES HE, Andrew Lambe, Beth Friedman, Delphine K. Farmer, John Seinfeld, Jeffrey R. Pierce, Shantanu Jathar, Colorado State University
Abstract Number: 254
Working Group: Aerosol Physics
Abstract
Environmental chambers and oxidation flow reactors (OFR) are used to study secondary organic aerosol (SOA) formation under a wide range of atmospheric aging times (hours to weeks). While SOA parameters used in atmospheric models are typically developed using chamber data, there is an opportunity to incorporate OFR data to improve their representation, especially over longer photochemical ages. In this work, we use a size-resolved chemistry and microphysics model, updated to represent nucleation, phase-state-limited gas/particle partitioning, oligomerization, wall loss, and heterogeneous chemistry, to simulate SOA formation from the photooxidation of α-pinene in chamber and OFR experiments. We argue that we can develop consistent SOA parameterizations across chamber and OFR data by accounting for, most importantly, nucleation dynamics in OFRs from low-volatility oxidation products, including highly oxygenated organic molecules (HOM). Preliminary OFR simulations show that: (1) nucleation dynamics can significantly affect the simulated SOA mass yield and size distribution and gas-phase fragmentation can decrease the SOA mass yield at longer photochemical ages (>5 days); (2) phase-state-limited gas/particle partitioning has a marginal influence on SOA formation due to the elevated relative humidity (30-40%) that leads to less viscous aerosols; and (3) heterogeneous chemistry has little effect on both the SOA mass yield and size distribution. Furthermore, we find that when the nucleation rate is linked to the concentration of low-volatility species (including HOMs), we can not only reproduce the measured size distributions from the OFR experiments but also reproduce observations of SOA mass and O:C in both the chamber and OFR experiments. Ongoing work is focused on developing OFR-informed parameters for other SOA precursors (e.g., n-dodecane, toluene) and applying these updated parameterizations in chemical transport models to study SOA evolution over longer timescales.