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Published April 1, 2006 | Supplemental Material
Journal Article Open

Contribution of First- versus Second-Generation Products to Secondary Organic Aerosols Formed in the Oxidation of Biogenic Hydrocarbons


Biogenic hydrocarbons emitted by vegetation are important contributors to secondary organic aerosol (SOA), but the aerosol formation mechanisms are incompletely understood. In this study, the formation of aerosols and gas-phase products from the ozonolysis and photooxidation of a series of biogenic hydrocarbons (isoprene, 8 monoterpenes, 4 sesquiterpenes, and 3 oxygenated terpenes) are examined. By comparing aerosol growth (measured by Differential Mobility Analyzers, DMAs) and gas-phase concentrations (monitored by a Proton Transfer Reaction Mass Spectrometer, PTR-MS), we study the general mechanisms of SOA formation. Aerosol growth data are presented in terms of a "growth curve", a plot of aerosol mass formed versus the amount of hydrocarbon reacted. From the shapes of the growth curves, it is found that all the hydrocarbons studied can be classified into two groups based entirely on the number of double bonds of the hydrocarbon, regardless of the reaction systems (ozonolysis or photooxidation) and the types of hydrocarbons studied:  compounds with only one double bond and compounds with more than one double bond. For compounds with only one double bond, the first oxidation step is rate-limiting, and aerosols are formed mainly from low volatility first-generation oxidation products; whereas for compounds with more than one double bond, the second oxidation step may also be rate-limiting and second-generation products contribute substantially to SOA growth. This behavior is characterized by a vertical section in the growth curve, in which continued aerosol growth is observed even after all the parent hydrocarbon is consumed.

Additional Information

© 2006 American Chemical Society. Received for review November 10, 2005. Revised manuscript received January 24, 2006. Accepted February 6, 2006. This research was funded by the U.S. Environmental Protection Agency Science to Achieve Results (STAR) Program Grant Number RD-83107501-0, managed by EPA's Office of Research and Development (ORD), National Center for Environmental Research (NCER), and by U.S. Department of Energy Biological and Environmental Research Program DE-FG02-05ER63983. The University of California contribution to this material is based upon work supported by the National Science Foundation under Grant No. 0443448 and 0119510 and the California Air Resources Board (Contract 00-732). The authors would like to thank Neil M. Donahue for helpful discussions.

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