AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Secondary Organic Aerosol Oligomerization, Particle Viscosity, and the Trapping of Volatiles in the Aerosol Phase
DAVID DE HAAN, Melissa Galloway, Nahzaneen Sedehi, Jonathan Bartolomucci, University of San Diego
Abstract Number: 155 Working Group: Aerosol Chemistry
Abstract Organic aerosol particles were originally thought of as liquid mixtures. However, recent discoveries of the presence of oligomers in organic aerosol, combined with observations of kinetically-limited evaporation processes in these particles, have led to the idea that oligomerized organic aerosol particles can be highly viscous, or “glassy.” We examine aldehyde + ammonium sulfate and aldehyde + amine reactions that are known to produce oligomers in lab aerosol under certain conditions. Vibrating orifice droplet generation studies indicate that many aldehyde + AS reactions can occur during droplet evaporation, and some of these reaction products do not evaporate from the droplets as they dry, even after many minutes. Furthermore, in some cases these aerosol-phase products represent greater than 100% of the starting aldehyde by volume, indicating that significant amounts of water are also trapped in the product mixture. This effect is especially pronounced in experiments done under cloud-like conditions, where initial concentrations of aldehydes in the VOAG droplets are in the low micromolar range. These results can be rationalized if the evaporating droplet becomes viscous due to fast oligomer formation by the aldehyde + AS reactions.