Spatial characteristics of nitro- and oxy-PAHs during winter in Northeast Asia

In this study, 8 nitro-PAHs (nPAHs) and 10 oxy-PAHs (oPAHs) were analyzed in the PM 2.5 samples collected from four sites of Northeast Asia during the winter season to evaluate their spatial distribution. The total mean concentrations of nPAHs and oPAHs were extremely high in Ulaanbaatar (UB) as 318.80 ± 176.35 ng/m³. In Beijing (BJ), Seoul (SE), and Seosan (SS), the concentrations were similar at 25.59 ± 13.25 ng/m³, 15.51 ± 3.12 ng/m³, and 25.14 ± 21.98 ng/m³, respectively. oPAHs concentrations were higher than nPAHs at all sampling sites, being 107 times higher in UB and approximately 22 times higher at the other three sites. The distribution of individual compounds were similar in BJ, SE, and SS, while, UB showed distinct characteristics. To assess which factor is more significant between the primary emission and secondary formation of nPAHs and oPAHs, correlation and PMF analyses with the other air pollutants were conducted. Although the main factor for determining of nPAHs and oPAHs was different by location, secondary formation (54.5 %) and vehicle exhaust (34.3 %) were the main factors to occur nPAHs in the atmosphere, while oPAHs were mainly determined by solid coal combustion (44.2 %) and vehicle exhaust (39.1 %). In particular, secondary formation by heterogeneous reaction appeared to be a significant factor for nPAHs in SE. In the Monte Carlo simulations for Incremental Lifetime Cancer Risk (ILCR) assessment, males had higher average ILCR values than females, especially in the 0–1 age group. Excluding the male 0–1 age group in UB, all other groups were found to be within acceptable levels (ILCR <1.0 E⁻⁶) of carcinogenic risk. The cancer risk in UB was significantly driven by the high concentrations of parent PAHs, rather than oPAHs and nPAHs.