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Environ Sci Technol

Title:		Direct photolysis of alpha-pinene ozonolysis secondary organic aerosol: effect on particle mass and peroxide content
Author(s):		Epstein SA; Blair SL; Nizkorodov SA;
Address:		"Department of Chemistry, University of California , Irvine, California 92697, United States"
Journal Title:		Environ Sci Technol
Year:		2014
Volume:		20140910
Issue:		19
Page Number:		11251 - 11258
DOI:		10.1021/es502350u
ISSN/ISBN:		1520-5851 (Electronic) 0013-936X (Linking)
Abstract:		"Primary and secondary organic aerosols (POA and SOA) contain a complex mixture of multifunctional chemicals, many of which are photolabile. Much of the previous work that aimed to understand the chemical evolution (aging) of POA and SOA has focused on the reactive uptake of gas-phase oxidants by particles. By stripping volatile compounds and ozone from alpha-pinene ozonolysis SOA with three 1-m-long denuders, and exposing the residual particles in a flow cell to near-ultraviolet (lambda>300 nm) radiation, we find that condensed-phase photochemistry can induce significant changes in SOA particle size and chemical composition. The particle-bound organic peroxides, which are highly abundant in alpha-pinene ozonolysis SOA (22 +/- 5% by weight), have an atmospheric photolysis lifetime of about 6 days at a 24-h average solar zenith angle (SZA) of 65 degrees experienced at 34 degrees latitude (Los Angeles) in the summer. In addition, the particle diameter shrinks 0.56% per day under these irradiation conditions as a result of the loss of volatile photolysis products. Experiments with and without the denuders show similar results, suggesting that condensed-phase processes dominate over heterogeneous reactions of particles with organic vapors, excess ozone, and gas-phase free radicals. These condensed-phase photochemical processes occur on atmospherically relevant time scales and should be considered when modeling the evolution of organic aerosol in the atmosphere"
Keywords:		Aerosols/analysis/*chemistry Air Pollutants/*chemistry Atmosphere/chemistry Bicyclic Monoterpenes Gases Los Angeles Monoterpenes/*chemistry Ozone/*chemistry Particle Size Peroxides/chemistry Photolysis Seasons;
Notes:		"MedlineEpstein, Scott A Blair, Sandra L Nizkorodov, Sergey A eng Research Support, U.S. Gov't, Non-P.H.S. 2014/08/29 Environ Sci Technol. 2014 Oct 7; 48(19):11251-8. doi: 10.1021/es502350u. Epub 2014 Sep 10"