Seasonal variation and gas/particle partitioning of atmospheric halogenated polycyclic aromatic hydrocarbons and the effects of meteorological conditions in Ulsan, South Korea

Atmospheric halogenated polycyclic aromatic hydrocarbons (Halo-PAHs) and parent PAHs were monitored in Ulsan, South Korea for one year (January‒December 2015) to investigate their seasonal patterns, gas/particle partitioning behavior, and the impact of meteorological conditions. The mean concentrations of 24 chlorinated PAHs, 11 brominated PAHs, and 13 parent PAHs in the gaseous and particulate phases were 8.64 and 9.64 pg/m³, 11.6 and 1.62 pg/m³, and 2.17 and 2.40 ng/m³, respectively. Winter had the highest ClPAH and PAH levels, with significant contributions from poly-chlorine groups and high-molecular-weight compounds. However, BrPAHs showed reverse patterns with the highest concentration in summer and the dominant gaseous fraction throughout the year. This finding could be explained by the strong local sources of BrPAHs, related to automobile and petrochemical industries. In contrast, the effects of the temperature inversion layer and atmospheric transport from the outside of Ulsan were more apparent for ClPAHs and PAHs, particularly in winter and spring. Regarding gas/particle partitioning, Halo-PAHs exhibited different seasonal behaviors from those of parent PAHs. The sorption pathway of Halo-PAHs seemed to shift from absorption as the sole dominant mechanism in winter and spring to both adsorption and absorption in summer and fall, while both partitioning mechanisms contributed equally for parent PAHs during the entire year. This study implies that Halo-PAHs and parent PAHs might not share the same atmospheric behavior, possibly due to different characteristics in atmospheric reactions with other chemicals and particle-size distribution. However, there have been limited studies about the formation of Halo-PAHs and their physicochemical properties; hence, further in-depth investigations are of vital importance.