Web Release Date: July 16,
Products and Mechanisms of Ozone Reactions with Oleic Acid for Aerosol Particles Having Core-Shell Morphologies
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Division of Engineering and Applied Sciences, 29 Oxford St., Pierce Hall, Room 122, Harvard University, Cambridge, Massachusetts 02138, Department of Environmental Sciences, Weizmann Institute, Rehovot 76100, Israel, Chemistry Department, Boston College, Chestnut Hill, Massachusetts 02467, and Aerodyne Research, Inc., 45 Manning Road, Billerica, Massachusetts 08121-3976
Received: January 16, 2004
In Final Form: April 28, 2004
Abstract:
Heterogeneous reactions of oleic acid aerosol particles with ozone are studied below 1% relative humidity. The particles have inert polystyrene latex cores (101-nm diameter) coated by oleic acid layers of 2 to 30 nm. The chemical content of the organic layer is monitored with increasing ozone exposure by using an aerosol mass spectrometer. The carbon-normalized percent yields of particle-phase reaction products are 20-35% 9-oxononanoic acid, 1-3% azelaic acid, 1-3% nonanoic acid, and 35-50% other organic molecules (designated as CHOT). There is approximately 25% evaporation, presumably as 1-nonanal. To explain the formation of CHOT molecules and the low yields of azelaic and nonanoic acids, we suggest a chemical mechanism in which the Criegee biradical precursors to azelaic acid and nonanoic acid are scavenged by oleic acid to form CHOT molecules. These chemical reactions increase the carbon-normalized oxygen content (z/x) of the CxHyOz layer from 0.1 for unreacted oleic acid to 0.25 after high ozone exposure. Under the assumption that oxygen content is a predictor of hygroscopicity, our results suggest an increased cloud condensation nuclei activity of atmospherically aged organic particles that initially have alkene functionalities.
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