Atmos. Chem. Phys. Discuss., 13, 7151-7174, 2013
www.atmos-chem-phys-discuss.net/13/7151/2013/
doi:10.5194/acpd-13-7151-2013
© Author(s) 2013. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Self-limited uptake of α-pinene-oxide to acidic aerosol: the effects of liquid-liquid phase separation and implications for the formation of secondary organic aerosol and organosulfates from epoxides
G. T. Drozd, J. L. Woo, and V. F. McNeill
Department of Chemical Engineering, Columbia University, New York, NY, 10027, USA

Abstract. The reactive uptake of α-pinene oxide (αPO) to acidic sulfate aerosol was studied under humid conditions in order to gain insight into the effects of liquid-liquid phase separation on aerosol heterogeneous chemistry and further elucidate the formation of secondary organic aerosol and organosulfates from epoxides. A continuous flow environmental chamber was used to monitor changes in diameter of monodisperse, deliquesced, acidic sulfate particles exposed to αPO at 30 and 50% RH. In order to induce phase separation and probe potential limits to particle growth from acidic uptake, αPO was introduced over a wide range of concentrations, from 200 ppb to 5 ppm. Uptake was observed to be highly dependent on initial aerosol pH. Significant uptake of αPO to aerosol was observed with initial pH < 0. When exposed to 200 ppb αPO, aerosol with pH = −1 doubled in volume, and 6% volume growth was observed at pH = 0. Aerosol with pH = 1 showed no growth. The extreme acidity required for efficient αPO uptake suggests that this chemistry is typically not a major route to formation of aerosol mass or organosulfates in the atmosphere. Partition coefficients (Kp) ranged from 0.2–1.6 × 10−4 m3 μg−1 and were correlated to initial particle acidity and particle organic content; particles with higher organic content had lower partition coefficients. Effective uptake coefficients (γ) ranged from 0.4 to 4.7 × 10−5 and are much lower than recently reported for uptake to bulk solutions. In experiments in which αPO was added to bulk H2SO4 solutions, phase separation was observed for mass loadings similar to those observed with particles, and product distributions were dependent on acid concentration. Liquid-liquid phase separation in bulk experiments, along with our observations of decreased uptake to particles with the largest growth factors, suggest an organic coating forms upon uptake to particles, limiting reactive uptake.

Citation: Drozd, G. T., Woo, J. L., and McNeill, V. F.: Self-limited uptake of α-pinene-oxide to acidic aerosol: the effects of liquid-liquid phase separation and implications for the formation of secondary organic aerosol and organosulfates from epoxides, Atmos. Chem. Phys. Discuss., 13, 7151-7174, doi:10.5194/acpd-13-7151-2013, 2013.
 
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