Gas-particle partitioning of semi-volatile organic compounds to model atmospheric particulate materials—I. Sorption to graphite, sodium chloride, alumina, and silica particles under low humidity conditions

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Abstract The partitioning of seven polycyclic aromatic hydrocarbons (PAHs) to four model atmospheric particulate materials (APM) in dry nitrogen is examined. Literature data involving the development of a photoelectric aerosol sensor for the quantitation of particulate PAHs are reanalysed in an atmospheric gas-particle partitioning context. The PAHs include chrysene and benz[a]anthracene, three benzofluoranthenes, benzo[a]pyrene, and benzo[e]pyrene. The model sorbents include graphitic carbon, sodium chloride, silica, and alumina. The measured partition coefficients are expressed in both a Kp(m3μg−1) and a Kp,s(m3m−2) format, and are compared to corresponding values for urban particulate material (UPM) at ambient relative humidity (r.h.). The partition coefficient Kp is the ratio of the sorbed concentration (ng μg−1) to the gaseous concentration (ng m−3). The partition coefficient Kp,s is the ration of the surface-area normalized sorbed concentration (ng m−2) to the gaseous concentration (ng m−3). Estimates of the compound-dependent heats of desorption from the surfaces(Q1, kJ mol−1) are determined from the slopes of plots of measured values of log K p ( or log K p,s ) vs 1 T . For graphitic carbon, a surface that might have been expected to sorb compounds in a non-specific manner, the agreement between the measured log K p,s vs 1 T lines and extrapolated UPM lines is very reasonable. The agreement was not as good for the other three sorbents. Silica and alumina exhibited significantly stronger sorption than UPM on a Kp,s basis. However, the Q1 estimates determined for silica and alumina were not found to be as high as might have been expected under these circumstances; the quality of the Q1 data is therefore in question. The general agreement between the log K p,s vs 1 T plots for graphitic carbon in dry nitrogen with those for UPM at ambient r.h. adds further evidence to the argument that partitioning to UPM is a d sorptive, and non-specific in nature.