Tokyo and its neighboring prefectures will debut regulations Wednesday to curb emissions from diesel-powered trucks and buses to clear up the region's air pollution problem -- the nation's worst.
It is the first attempt by local governments to jointly impose stricter regulations than those set by the national government to control particulate matter emissions from diesel vehicles.
According to the Tokyo Metropolitan Government, the density of suspended particulate matter in all monitoring points in Tokyo in 2002 surpassed the national government's acceptable levels. SPM is the fine black soot emitted from vehicle engines, especially diesels, and is believed to cause respiratory problems, including asthma.