GAS PARTICLE PARTITIONING OF SEMIVOLATILE ORGANIC-COMPOUNDS TO MODEL INORGANIC, ORGANIC, AND AMBIENT SMOG AEROSOLS/

Gas/particle (G/P) partitioning is an important process that affects t he deposition, chemical reactions, long-range transport, and impact on human and ecosystem health of atmospheric semivolatile organic compou nds (SOCs). Gas/particle partitioning coefficients (K-p) were measured in an outdoor chamber for a group of polynuclear aromatic hydrocarbon s (PAHs) and n-alkanes sorbing to three types of model aerosol materia ls: solid ammonium sulfate, liquid dioctyl phthalate (DOP), and second ary organic aerosol (SOA) generated from the photooxidation of whole g asoline vapor. K-p values were also measured for ambient n-alkanes sor bing to urban particulate material (UPM) during summer smog episodes i n 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 o rganic fraction in the aerosol. Comparisons of the partitioning of SOC s to three different types of aerosols demonstrate that (1) DOP aeroso l may he a good surrogate for ambient aerosol that consists mainly of organic compounds from primary emissions; (2) ETS particles may be a g ood 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-ge nerated SOA from gasoline support the use of literature SOA yield data from smog chamber studies to predict the extent of SOA formation duri ng summer midday smog episodes.