Insights into the Gradual Decreasing Trend of PM_2.5: Before the Notification of Environmental Standard (2000–2008)

Abstract

Before the environmental standard value for PM_2.5 was introduced in 2009, the observed PM_2.5 in Japan showed the gradual decreasing trend. In this study, in order to clarify the reason of this gradual decreasing trend of PM_2.5, the long-term source apportionments of PM_2.5 in Japan during 2000–2008 were evaluated based on the air quality model by applying the tagged tracer method. The source groups were divided into total of 11; six domestic anthropogenic sources, three foreign anthropogenic sources from China, Korea, and other regions, and ship and natural sources. The performances of the air quality model were validated by a statistical analysis, and confirmed that the modeling system satisfied the model performance criteria. The domestic anthropogenic sources were higher than the abroad anthropogenic source on 2000–2001; and subsequently the relationships were reversed. This increasing abroad anthropogenic sources was mainly caused by the impact from China. The source apportionment of abroad anthropogenic sources had increased; however, due to the decline of natural sources and significant decline of domestic automobile sources (p<0.001), it was clarified that PM_2.5 in Japan showed the gradual decreasing trend. Other sources of power plant, industry, domestic, and others in Japan showed unclear trends.