Gas/Particle Partitioning of Semivolatile Organic Compounds To Model Inorganic, Organic, and Ambient Smog Aerosols

Abstract

Gas/particle (G/P) partitioning is an important process that affects the deposition, chemical reactions, long-range transport, and impact on human and ecosystem health of atmospheric semivolatile organic compounds (SOCs). Gas/particle partitioning coefficients (K_p) were measured in an outdoor chamber for a group of polynuclear aromatic hydrocarbons (PAHs) and n-alkanes sorbing to three types of model aerosol materials:  solid ammonium sulfate, liquid dioctyl phthalate (DOP), and secondary organic aerosol (SOA) generated from the photooxidation of whole gasoline vapor. K_p values were also measured for ambient n-alkanes sorbing to urban particulate material (UPM) during summer smog episodes in the Los Angeles metropolitan area. Based on the K_p values obtained for the aerosols studied here, for environmental tobacco smoke (ETS), and for a quartz surface, we conclude that G/P partitioning of SOCs to UPM during summer smog episodes is dominated by absorption into the organic fraction in the aerosol. Comparisons of the partitioning of SOCs to three different types of aerosols demonstrate that (1) DOP aerosol may be a good surrogate for ambient aerosol that consists mainly of organic compounds from primary emissions; (2) ETS particles may be a good surrogate for SOA; and (3) the sorption properties of ambient smog aerosol and the chamber-generated SOA from gasoline are very similar. The similarities observed between ambient smog aerosol and chamber-generated SOA from gasoline support the use of literature SOA yield data from smog chamber studies to predict the extent of SOA formation during summer midday smog episodes.