AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Secondary Organic Aerosol Formation from Acid-Catalyzed Uptake of α-Pinene Oxide to Aqueous Sulfate Particles
JOSEPH WOO, Greg Drozd, Allison Schwier, V. Faye McNeill, Columbia University
Abstract Number: 748 Working Group: Aerosol Chemistry
Abstract Significant uptake of alpha-pinene oxide (aPO) onto ammonium sulfate and sulfuric acid aerosol has been observed and characterized. Size-selected, monodisperse aerosol samples were exposed to gas-phase aPO at concentrations ranging from 0.2-5ppm in a continuous flow 3.5m$^3 PTFE chamber, at relative humidities 30-60±5%. Uptake of aPO onto sampled aerosols under these conditions was measured via scanning mobility particle sizer (SMPS), indicating volume increases of up to 270% of their original values.
Aerosol growth was shown to be a strong function of initial particle pH, which is consistent with acid-catalyzed formation of alpha pinene oxide-derived diol (aPO-diol) and organosulfate (aPO-OS) species. Observed total mass uptake was also enhanced by increased gas-phase aPO concentrations and initial aerosol size.
Based on the expected O:C ratio of the particles, liquid-liquid phase separation is expected. Continued particle growth is observed even at high growth factors, suggesting that, even when organic content is high, acidic water continues to be accessible for uptake of aPO. However, the partitioning coefficient for aPO decreases with increasing growth factor, suggesting that uptake becomes less efficient.