Characteristics of PM2.5 in Hachinohe, the priority pollution control city in Japan

In the urban area of Hachinohe, Japan, PM_2.5 sampling was carried out from May 2015 to February 2021. The average concentration of PM_2.5 during the entire sampling period was approximately 11.7 μg m⁻³, with 4.4 μg m⁻³ for water soluble ions, 3.3 μg m⁻³ for carbonaceous species, 0.5 μg m⁻³ for trace metals, and 3.5 μg m⁻³ for other species. Based on this comprehensive component information, eight sources were quantitatively explored, among which ship emissions (29%), traffic emissions (19%), and secondary organic aerosols (15%) had relatively high contributions for PM_2.5 concentration level. The health risk assessment indicated that the children in Hachinohe City faced serious non-carcinogenic and carcinogenic risks, with corresponding values of 8.0 for HI and 1.2 × 10⁻⁴ for CR. The pollutants from ship emissions, secondary nitrates plus coal combustion, and industrial emissions should be of concern. High risk metals included Pb, As, Sb, V, and Cr(VI). Specifically, ship emissions exhibited the highest concentration (5.5 μg m⁻³) and health risks (HI = 2.2 and CR = 3.0 × 10⁻⁵) in summer; priority should be given to controlling pollution in the Port of Hachinohe. The other two sources had the highest concentration in winter (2.0 and 0.5 μg m⁻³) and were mainly influenced by the polluted air masses from Akita Prefecture, with HI values of 2.4 and 2.5 and CR values of 4.9 × 10⁻⁵ and 3.2 × 10⁻⁵, respectively. Overall, our study comprehensively revealed the characteristics of PM_2.5 in Hachinohe City and conducted an in-depth investigated into its causes of pollution. This information could serve as a scientific basis for developing specific strategies to improve air quality.