Trends of concentrations of suspended particle matter (SPM) from FY 1996 to in urban areas of the Kanto district, such as Tokyo, Kanagawa and Saitama prefectures were analyzed in the context of policies and regulations adopted for emission control, especially to separate the effects of regulations for automobiles and incinerators.
The Contribution of primary particles from automobiles to the ambient monitoring stations is estimated by assuming that it is in proportion to the difference of concentration measured at all the road-side monitoring stations and ambient monitoring stations in a prefecture. As a result, the contribution of automobiles to SPM concentration at ambient monitoring stations appears to have decreased remarkably over a nine year period in these areas.
The contribution of NOx (= NO+ NO₂) by automobiles, however, has slightly decreased during the same period.
The contribution of incinerators to SPM concentration was estimated next, since the regulations for the emission of dioxins started in 2000, which could have affected SPM concentrations. Since the concentrationsof dioxins were in good correlation with SPM concentrations at ambient monitoring stations, with the subtraction of contribution of the primary particles from automobiles, the linear regression between those two kinds of substances was assumed. The results indicated the regulations for dioxins appeared to contribute great deal to the decrease in SPM concentrations. The contribution of the primary particles from these two kinds of emission sources to the total SPM concentration has decreased, thus the secondary particles observed in the summer season become more noticeable.