Aerosol formation from atmospheric hydrocarbon photooxidation

Author: Forstner, Hali J. L.

Year: 1996

Degree: Dissertation (Ph.D.)

Advisors: Seinfeld, John H.; Flagan, Richard C.

Committee Member: Unknown, Unknown

Option: Environmental Science and Engineering

DOI: 10.7907/khpq-7188

Abstract

Outdoor smog chamber experiments have been performed to determine the secondary organic aerosol (SOA) formation potential of various C7, C8, and C9 aromatics in sunlight-irradiated hydrocarbon- NO[subscript x] mixtures. Measured aerosol yields from toluene,m-xylene, p -xylene, ethylbenzene, m -ethyltoluene, p-ethyltoluene, and 1 ,2,4-trimethylbenzene were found to correlate with organic mass concentration according to semi-volatile gas/particle partitioning theory. Aerosol yields of the C9 aromatics were greater than those of the C8 aromatics, with m-ethyltoluene resulting in the greatest yields. Toluene and ethylbenzene demonstrated some aerosol-forming potential, but the other aromatics produced significantly more SOA.

Filter samples were also collected during the experiments to determine the molecular composition of the SOA from these aromatics Gas-phase mechanisms leading to these products have been proposed. Unsaturated anhydrides (2,5-furandione, 3-methyl-2,5-furandione, 3-ethyl-2,5-furandione) are predominant components of aerosol from all the aromatics, an observation that is consistent with gas-phase aromatic mechanisms involving ring-fragmentation. Saturated anhydrides were also detected in significant quantities, which could result from the hydrogenation of furandiones in sunlight in the particle phase. A new organic aerosol extraction procedure utilizing supercritical CO2 extraction is outlined.

Outdoor smog chamber experiments were also performed to characterize aerosol from 1-octene and 1-decene photooxidation. The dominant aerosol species were heptanal, heptanoic acid, and dihydro-5-propyl-2(3H)-furanone from 1-octene, and nonanal, nonanoic acid, and dihydro-5-pentyl-2(3H)-furanone from 1-decene. Gas-phase oxidation mechanisms of 1-octene and 1-decene with OH and O3 account for the aerosol products.

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