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Particulate matter (PM) in 11 different sizes was collected at a semi-rural site in Ulsan, a multi-industrial city in South Korea, over one year from 2019 to 2020 to investigate the temporal patterns in size distribution and potential sources of polycyclic aromatic hydrocarbons (PAHs). The mean concentration of Σ 21 PAHs was higher in winter (0.29 and 0.45 ng/m3 for coarse and fine PM, respectively) than in summer (0.06 and 0.07 ng/m3). Although there was no statistically significant difference between day and night for the concentration of individual PAHs in both coarse and fine PM, the concentrations were generally higher during the day than at night. During the day, Σ 21 PAHs had two distinct peaks (0.056–0.10 μm and 3.20–5.60 μm) in winter, but they tended to partition to larger particles (1.00–1.80 μm and >18.0 μm) in summer. This result suggests that the volatilization of PAHs in smaller particles was enhanced by high-temperature conditions in summer, followed by their condensation onto larger particles. At night, Σ 21 PAH peaks were mainly around the size of 0.7 μm (droplet mode), suggesting the importance of heterogeneous-aqueous reactions. The results of the conditional bivariate probability function and concentration-weighted trajectory indicate that the high concentrations of PAHs in summer and winter were more affected by local pollution and long-range atmospheric transport, respectively. The results of the health risk assessment demonstrate that PAHs in fine PM contributed significantly to cancer risk compared to those in coarse PM. In conclusion, investigating the size distribution of PAHs in particles is necessary to understand their environmental behaviors and evaluate potential health risks. [Display omitted] • Polycyclic aromatic hydrocarbons (PAHs) were higher during the day than at night. • Day–night variation in the particle-size distribution of PAHs was apparent. • Long-range atmospheric transport became more significant in winter. • The concentration of PAHs in summer was more affected by local pollution. • Fine particles had a higher cancer risk of PAHs than coarse particles. [ABSTRACT FROM AUTHOR]

Chlorinated and brominated polycyclic aromatic hydrocarbons (ClPAHs and BrPAHs, respectively) are a new derivative group of PAHs. These halogenated PAHs (Halo-PAHs) have been reported to be carcinogenic and are considered emerging persistent organic pollutants. Gaining a clear understanding of the distribution and behavior of these ubiquitous organic pollutants is essential for the control and mitigation of their emission into the environment. However, research into the characteristics of Halo-PAHs in the atmosphere has been somewhat limited. This review paper thus aims to provide an overview of the seasonal patterns, profiles, potential sources, and particle-size distributions of atmospheric ClPAHs and BrPAHs with 3–5 rings. Most previous studies have focused on particulate Halo-PAHs and reported that their levels are higher during the cold season than during the warm season, with this seasonal variation more apparent for ClPAHs than for BrPAHs. In terms of their phase distribution, ClPAHs and BrPAHs share a similar trend, with their gaseous concentrations highest in summer and lowest in winter and their particulate concentrations exhibiting the opposite trend. Halo-PAH profiles have been shown to differ between sampling locations, possibly reflecting differences in the potential sources present at these sites, e.g., coal burning, traffic emissions, and industrial activity. The majority of Halo-PAHs tend to accumulate as ultrafine particles with an aerodynamic diameter of less than 1.0 µm. Overall, a detailed understanding of the characteristics of Halo-PAHs in the atmosphere has yet to be achieved; hence, further research on atmospheric Halo-PAHs is necessary. [ABSTRACT FROM AUTHOR]

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. Image 1 • Winter had the highest ClPAH and PAH levels with significant contributions of HMWs. • Gaseous BrPAHs reached the maximum concentration in summer due to local sources. • The influence of LRAT on ClPAHs and PAHs was more apparent than on BrPAHs. • TILs were more frequent in winter, leading to higher levels of ClPAHs and PAHs. • The gas/particle partitioning mechanisms for Halo-PAHs were seasonally different. [ABSTRACT FROM AUTHOR]

Seoul, the capital of South Korea, is one of the largest megacities in northeast Asia. Previous studies have monitored atmospheric polycyclic aromatic hydrocarbons (PAHs) in Seoul, but few have produced highly spatially resolved data. In this study, a total of 144 polyurethane foam-passive air samplers (PUF-PASs) were deployed at 36 sites (4 road, 26 urban, and 6 background sites) in Seoul during the summer of 2016 and the winter of 2017. The concentrations of Σ 13 PAHs fell within a range of 2.6–49.9 ng/m3 in summer and 15.5–77.8 ng/m3 in winter. Low-molecular-weight PAHs with 3–4 rings were dominant (accounting for about 97% of all PAHs) at all sampling sites in both seasons compared to high-molecular-weight PAHs with 5–6 rings. Phenanthrene was the most abundant individual compound, accounting for 35–54% and 42–52% of the total PAHs in summer and winter, respectively. The spatial distribution of PAHs was determined by traffic, domestic heating, topography, transport, and meteorological conditions. The concentration of PAHs at the road sites was higher than at the urban and background sites, indicating that vehicular exhaust was a major source in both seasons. In addition, diagnostic ratios and principal component analysis revealed the influence of various sources, such as gasoline and diesel emissions and coal and biomass combustion. Backward air trajectory analysis highlighted the influence of long-range transport from northern China and North Korea during the winter, whereas the influence of local emissions and satellite cities appeared to dominate during the summer. In conclusion, passive air sampling was successfully employed to identify major sources of PAHs in an Asian megacity, indicating that it could produce data with a high spatial resolution for use in human risk assessment and air monitoring networks. • Passive air sampling was conducted at 36 sites in Seoul, Korea in summer and winter. • The mean concentration of PAHs in winter was higher than that in summer. • Road sites exhibited higher levels of PAHs than urban and background sites. • The influence of long-range transport was evident during the winter. • The influence of local emissions and satellite cities was dominant during the summer. [ABSTRACT FROM AUTHOR]