In October 2003, the Tokyo Metropolitan Government began regulating emissions from diesel-powered trucks and buses under a local in-use particulate emission standard. This paper uses an empirically based emissions modeling approach to estimate the effect of Tokyo's regulations on emissions of particulate matter and nitrogen oxides. Results indicate that Tokyo's regulations cut exhaust particulate emissions from diesel-powered trucks and buses registered in Tokyo by 17% and 31% in 2003 and 2004 through the promotion of diesel particulate filters and oxidation catalysts and by accelerating fleet turnover. Modest emission reductions were also observed for nitrogen oxides. The model suggests that the bulk of emission reductions - 70% for particulate matter, and 30% for nitrogen oxides - after 2002 directly tied to environmental policies are attributable to Tokyo's local regulations rather than national emission control policies.
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