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Environ Sci Technol

Title:		Particle-phase chemistry of secondary organic material: modeled compared to measured O:C and H:C elemental ratios provide constraints
Author(s):		Chen Q; Liu Y; Donahue NM; Shilling JE; Martin ST;
Address:		"School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA"
Journal Title:		Environ Sci Technol
Year:		2011
Volume:		20110511
Issue:		11
Page Number:		4763 - 4770
DOI:		10.1021/es104398s
ISSN/ISBN:		1520-5851 (Electronic) 0013-936X (Linking)
Abstract:		"Chemical mechanisms for the production of secondary organic material (SOM) are developed in focused laboratory studies but widely used in the complex modeling context of the atmosphere. Given this extrapolation, a stringent testing of the mechanisms is important. In addition to particle mass yield as a typical standard for model-measurement comparison, particle composition expressed as O:C and H:C elemental ratios can serve as a higher dimensional constraint. A paradigm for doing so is developed herein for SOM production from a C(5)-C(10)-C(15) terpene sequence, namely isoprene, alpha-pinene, and beta-caryopyhllene. The model MCM-SIMPOL is introduced based on the Master Chemical Mechanism (MCM v3.2) and a group contribution method for vapor pressures (SIMPOL). The O:C and H:C ratios of the SOM are measured using an Aerosol Mass Spectrometer (AMS). Detailed SOM-specific AMS calibrations for the organic contribution to the H(2)O(+) and CO(+) ions indicate that published O:C and H:C ratios for SOM are systematically too low. Overall, the measurement-model gap was small for particle mass yield but significant for particle-average elemental composition. The implication is that a key chemical pathway is missing from the chemical mechanism. The data can be explained by the particle-phase homolytic decomposition of organic hydroperoxides and subsequent alkyl-radical-promoted oligomerization"
Keywords:		"Aerosols Mass Spectrometry *Models, Chemical Particulate Matter/*chemistry Peroxides/chemistry Volatile Organic Compounds/*chemistry;"
Notes:		"MedlineChen, Qi Liu, Yingjun Donahue, Neil M Shilling, John E Martin, Scot T eng Research Support, U.S. Gov't, Non-P.H.S. 2011/05/13 Environ Sci Technol. 2011 Jun 1; 45(11):4763-70. doi: 10.1021/es104398s. Epub 2011 May 11"