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GEOPHYSICAL RESEARCH LETTERS, VOL. 32, L18808, doi:10.1029/2005GL023637, 2005

Secondary organic aerosol formation from isoprene photooxidation under high-NO_x conditions

Jesse H. Kroll

Department of Environmental Science and Engineering and Department of Chemical Engineering, California Institute of Technology, Pasadena, California, USA

Nga L. Ng

Department of Environmental Science and Engineering and Department of Chemical Engineering, California Institute of Technology, Pasadena, California, USA

Shane M. Murphy

Department of Environmental Science and Engineering and Department of Chemical Engineering, California Institute of Technology, Pasadena, California, USA

Richard C. Flagan

Department of Environmental Science and Engineering and Department of Chemical Engineering, California Institute of Technology, Pasadena, California, USA

John H. Seinfeld

Department of Environmental Science and Engineering and Department of Chemical Engineering, California Institute of Technology, Pasadena, California, USA

Abstract

The oxidation of isoprene (2-methyl-1,3-butadiene) is known to play a central role in the photochemistry of the troposphere, but is generally not considered to lead to the formation of secondary organic aerosol (SOA), due to the relatively high volatility of known reaction products. However, in the chamber studies described here, we measure SOA production from isoprene photooxidation under high-NO _x conditions, at significantly lower isoprene concentrations than had been observed previously. Mass yields are low (0.9–3.0%), but because of large emissions, isoprene photooxidation may still contribute substantially to global SOA production. Results from photooxidation experiments of compounds structurally similar to isoprene (1,3-butadiene and 2- and 3-methyl-1-butene) suggest that SOA formation from isoprene oxidation proceeds from the further reaction of first-generation oxidation products (i.e., the oxidative attack of both double bonds). The gas-phase chemistry of such oxidation products is in general poorly characterized and warrants further study.

Received 26 May 2005; accepted 22 August 2005; published 23 September 2005.

Index Terms: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801, 4906); 0317 Atmospheric Composition and Structure: Chemical kinetic and photochemical properties; 0365 Atmospheric Composition and Structure: Troposphere: composition and chemistry.

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Citation: Kroll, J. H., N. L. Ng, S. M. Murphy, R. C. Flagan, and J. H. Seinfeld (2005), Secondary organic aerosol formation from isoprene photooxidation under high-NO_x conditions, Geophys. Res. Lett., 32, L18808, doi:10.1029/2005GL023637.

Copyright 2005 by the American Geophysical Union.