Clear Declining Behaviors and Causes in Atmospheric Polycyclic Aromatic Hydrocarbon Concentrations at the West End of Japan from 2017 to 2021

In order to determine recent behaviors in atmospheric polycyclic aromatic hydrocarbon (PAH) concentrations at the west end of Japan and to reveal the causes of these behaviors, atmospheric PAH concentrations were measured in suburban and forest sites of Nagasaki, Japan from 2017 to 2021. The results showed that the total concentration of PAHs decreased considerably by 60% and 57% in suburban and forest sites, respectively, over this period. When analyzed by season, the rate of decrease in winter was markedly high. Therefore, the decreasing behavior in PAH concentrations in Nagasaki in recent years was considered to be mainly due to less PAHs originating from cold continental regions such as northern China. In particular, the reduction in coal and biomass combustion for winter heating in households, the efforts to improve air quality, and the limitation of economic activities in response to COVID-19 were likely responsible for the decrease in atmospheric PAH concentrations. In addition, although the PAH concentrations decreased, there was no significant change in the breakdown of the number of benzene rings in the PAH or in the attributes of their sources