Temporal variation, size distribution and source identification of polycyclic aromatic hydrocarbons (PAHs) and water-soluble inorganic ions (WSIIs) in particulate matter in Ulsan, South Korea.

Abstract

This study investigated the seasonal variation and size distribution of particulate polycyclic aromatic hydrocarbons (PAHs) and water-soluble inorganic ions (WSIIs) during warm and cold seasons. 126 size-fractionated samples were collected using a six-stage cascade impactor sampler at a semi-rural area of Ulsan. The total concentration of PAHs and WSIIs were higher during the cold season (80.0 ng/m3 and 106.6 μg/m3, respectively) than during the warm season (13.85 ng/m3 and 33.72 μg/m3). This seasonal variation was attributed to different emission sources and prevailing meteorological conditions. In addition, PAHs and WSIIs accumulated in fine particles in the warm season (76% and 51% ), and cold season (88% and 66% ), respectively. In the case of WSIIs, Na+, Mg2+, Cl–, and Ca2+ were predominant in coarse particles, while K+, F–, NH4+, NO3–, and SO42– were dominant in fine particles. PAHs exhibited bimodal distributions, peaking at 0.39–0.69 μm and 1.3–2.1 μm in both seasons. On the contrary, WSIIs showed varying seasonal size distributions. During the warm season, NH4+, K+, and SO42– had unimodal distributions, peaking at 0.39–0.69 μm, and Ca2+ peaked at 4.2–10.2 μm, while Na+, Cl–, Mg2+, F–, and NO3– exhibited bimodal distribution with coarse peaks at 2.1–4.2 μm and 4.2–10.2 μm, and fine peaks at 0.39–0.69 μm and 1.3–2.1 μm. However, in the cold season, all the WSIIs except Cl– exhibited bimodal distribution. Na+, Mg2+, and Ca2+ peaked at 4.2–10.2 μm and 1.3–2.1 μm, while NH4+, K+, F–, NO3–, and SO42– peaked at 0.39–0.69 μm and 1.3–2.1 μm. Cl– had a trimodal distribution peaking at 0.39–0.69 μm, 1.3–2.1 μm, and 4.2–10.2 μm. BaP/BeP ratio, principal component analysis (PCA), diagnostic ratios (DRs), Spearman’s correlation analysis, and mole charge ratio were employed to determine potential emission sources of PAHs and WSIIs. The results showed that combustion/pyrogenic sources (i.e., biomass burning and coal combustion) and petrogenic sources (i.e., traffic emission, and petroleum combustion) were the major contributors to PAHs in both seasons. While the formation of secondary inorganic aerosols (SIA) in fine particles is by homogeneous oxidation, and for coarse particles, it was via heterogeneous reaction of their precursors onto coarse particles. In conclusion, PAHs and WSIIs showed apparent seasonal size variations. Estimated lifetime excess cancer risk via particulate-bound PAHs inhalation was within permissible limits, suggesting a generally low contamination profile with respect to the studied PAHs. The relative risk evaluation showed that inhalation of particulate-bound PAHs in the cold season could pose a higher likelihood of carcinogenic risks than in the warm season due to the relatively higher contamination profile of PAHs in the colder season.