Gas-particle partitioning of polycyclic aromatic hydrocarbons in urban, adjacent coastal, and continental background sites of western Greece

Particle- and gas-phase polycyclic aromatic hydrocarbons (PAHs) were collected from an urban, an adjacent coastal, and a continental background site located in Eordea basin, western Greece, to investigate their gas/particle distributions. Thirteen two- to six-ring PAHs, included in the U.S. EPA priority pollutant list, were determined in 24-h integrated glass fiber filters and polyurethane foam samples. At the prevailing ambient temperature levels, the three-ringed species (phenanthrene, anthracene) and the four-ringed fluoranthene and pyrene were primarily found in the gas phase. Conversely, the five- and six-ring PAHs were mainly associated with the particle phase. Gas/particle partitioning coefficients, K-P, were calculated, and their relationship with the subcooled liquid vapor pressure p(L)(O) of individual PAHs was investigated. Despite the large variability among samples, a good linear relationship between log K-P and log p(L)(O) was obtained for all sampling sites following the equation log K-P = m(r) log p(L)(O) + b(r). In the majority of sampling events, particularly in the adjacent coastal and the continental background sites, slopes (m(r)) were found to be shallower than the value of -1, which has been suggested as reflecting equilibrium partitioning. The deviations from predicted aerosol behavior observed in the present study may be attributed to several reasons, such as the presence of nonexchangeable PAH fraction, nonequilibrium as well as different particle characteristics.