AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Temperature Effects on Secondary Organic Aerosol Formation, Composition, and Phase State
MARY KACARAB, David R. Cocker III, University of California, Riverside
Abstract Number: 362 Working Group: Aerosol Chemistry
Abstract Temperature has been shown to have a profound effect on secondary organic aerosol (SOA) yield. Several terpene, aromatic, and cyclic alkene ozonolysis and photooxidation secondary organic aerosol systems were studied in the UC Riverside/CE-CERT dual 90m$^3 environmental chambers under different temperature cycles ranging from 278K to 313K. A non-reversible hysteresis effect was observed when cycling the temperature of experiments, demonstrating that the temperature at formation of the aerosol dictates the overall aerosol yield, with cold temperature experiments having drastically greater yields. Semi-volatile wall losses were explored for each system at different temperatures by comparing seeded and non-seeded experiments. Gas phase mass spectra were provided in real-time with a SYFT Technologies Selected Ion Flow Tube Mass Spectrometer (SIFT-MS). Bulk aerosol chemistry was monitored by an Aerodyne High Resolution Time of Flight Aerosol Mass Spectrometer (HR-ToF-AMS), finding that temperature has a noticeable effect on bulk elemental ratios and oxidation state. Physical properties of aerosol were also measured throughout experiments. Temperature has a noticeable effect on both particle volatility and hygroscopicity. Particle density, monitored with a Kanomax APM-SMPS, remains largely unaffected by temperature. It is hypothesized that at low temperature, aerosol may be in a glassy state and thus not follow traditional gas-particle partitioning models. Aerosol phase state is explored with an aerosol particle bounce instrument. The severe hysteresis effects seen in aerosol yields at different temperatures have strong implications for aerosol equilibration time and pose a challenge to current aerosol formation assumptions.