Insights into the characteristic variation of carbonaceous aerosols at a Japanese background site, Wajima from 2016 to 2021.

This study conducted a comprehensive analysis of the seasonal and interannual characteristics of organic carbon (OC), elemental carbon (EC) at the Kanazawa University Wajima Air Monitoring Station (KUWAMS), a background site in Japan, from 2016 to 2021. Typical anthropogenic pollutants, including nine polycyclic aromatic hydrocarbons and two biomass burning tracers were observed simultaneously. During the sampling periods, the highest concentrations of OC (0.84 μg/m3) and EC (0.10 μg/m3) were observed in spring, followed by winter (OC: 0.58 μg/m3; EC: 0.09 μg/m3), fall (OC: 0.47 μg/m3; EC: 0.06 μg/m3), and summer (OC: 0.24 μg/m3; EC: 0.03 μg/m3). In spring, fall, and winter, OC and EC concentrations were influenced by mixed contributions from fossil fuel combustion and biomass burning, while a relatively higher impact from traffic emission was observed in summer. Excluding the high polluted episode from fall 2018 to spring 2019, EC concentrations exhibited a significant decreasing trend in spring (z = -4.25, p < 0.01), fall (z = -7.70, p < 0.05), and winter (z = -7.80, p < 0.01) from 2016 to 2021, reflecting the effectiveness of continuous emission control measures implemented by the Chinese government. In contrast, OC concentrations did not present similar decreasing trends in cold seasons (spring: z = 7.35, p < 0.01; fall: z = 4.85, p < 0.01; winter: z = 2.45, p < 0.05), indicating a more complex formation mechanism for OC. These findings emphasize the necessity of improving OC emission control, particularly secondary OC, in upwind regions such as northern China and domestic Japan to mitigate atmospheric pollution and its impact on climate change.