Health risks and air quality by PM2.5 in the leeward area of the Asian continent in the preceding year of the MARPOL Treaty enforcement

The International Maritime Organization (IMO) has formulated stringent ship emission regulations, and the global fuel sulfur limit of 0.50% became effective in 2020. Kitakyushu City is in the coastal suburbs of western Japan, and PM_2.5 had already decreased prior to the global low-sulfur regulation, with concentrations in 2017, 2018, and 2019 of 12.2, 13.4, and 8.1 µg·m⁻³, respectively. The loading particles of the air masses passing through the Bohai Sea, Yellow Sea, and East China Sea in 2019 decreased to 3.4 µg·m⁻³, which was obviously higher than that of other air masses (0.5 µg·m⁻³), and the contribution of nss-SO₄²⁻ could reach 56%, followed by OC (23%) and NH₄⁺ (21%). Moreover, the characteristics of typical ship-emitted metals (V, Ni, As, Sb, W, and Cd) also changed greatly. Their sum concentrations in 2017, 2018, and 2019 were 10.6, 11.1, and 6.9 ng·m⁻³, respectively, which showed an annual variation similar to that of nss-SO₄²⁻. As for the particle exposure risk, the lowest chronic effect and carcinogenic risk were observed in 2019, with hazard indices (HI) for adults and children of 0.9 and 7.6, and carcinogenic risks (CRs) of 3.8 × 10⁻⁵ and 8.4 × 10⁻⁵, respectively. In this study, the health risks as well as air quality prior to the enforcement of the MARPOL Treaty in the leeward area of the Asian continent were totally and more precisely studied and evaluated based on the annual dataset; revealing the influence of trans-boundary transportation under individual Chinese regulations on the particle characteristic variations in Kitakyushu, Japan.