Variation of atmospheric PAHs in northern Taiwan during winter and summer seasons

Ambient air samples were collected simultaneously at three sites in winter and summer to investigate the characteristic variations of PAHs in northern Taiwan. In winter, the highest concentration was observed at urban site (225 ± 25.0 ng m^–3), followed by industrial and rural sites (173 ± 28.7 and 148 ± 12.9 ng m^–3, respectively). However, in summer, the highest PAHs concentration was measured at rural site (230 ± 8.0 ng m^–3), followed by urban and industrial sites (205 ± 29.2 and 200 ± 44.1 ng m^–3, respectively). Based on the air mass back trajectory, the air mass passing through more PAH sources before reaching the sampling site is the reason for higher PAH level being measured at rural site in summer. The highest BaP-TEQ concentration measured at rural site in summer suggests that human exposure to PAHs in summer should receive more attention. Based on the diagnostic ratios, samples collected at industrial site in two seasons are closely related to combustions of solid fuel and petroleum. At rural and urban sites, PAHs measured in winter are influenced by mixed sources of solid fuel/petroleum combustions and petroleum evaporation, while the sources of PAHs are more related to petroleum evaporation in summer. The gas/particle partitioning coefficients (K_p) correlated well with the sub-cooled liquid vapor pressures (P^oL) of PAHs with the slopes higher than –1 (the r² ranging from 0.835 to 0.909). The slope values indicate that both adsorption and absorption might govern gas/particle partitioning of PAHs. Comparison between different models reveals that adsorption of soot carbon is the major mechanism governing gas/particle partitioning.