How Shintaro Ishihara cleaned up Tokyo

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    Tokyo’s air quality gradually improved under former Tokyo Governor Shintaro Ishihara. Japan was behind the west in regulating atmospheric concentrations of known carcinogens such as PM2.5 – particulate matter smaller than 2.5 micrometers (µm). The primary source of these fine-sized particulates in Tokyo was diesel engines, which in 1999 Ishihara began a campaign to reduce.

    A law banning “dirty diesels” in Tokyo was passed in late 2000 and subsidies to help local businesses replace or retrofit noncompliant vehicles began in 2001. Enforcement through heavy fines as well as naming and shaming began from late 2003 in Tokyo, Saitama, Chiba, and (from 2004) Kanagawa. Upper limits on diesel exhaust were further lowered in 2006 [J].

    It wasn’t until 2009 that the central government introduced regulations comparable to those set by the US EPA: 35 and 15 micrograms per cubic meter (µg/m3) for daily- and yearly-averaged concentrations, respectively.

    The graph above shows the PM2.5 levels from fiscal year* 2000 to 2011, the limit of the raw data currently available from the Tokyo Metropolitan Government. There are only four long-term PM2.5 measuring stations in Tokyo (two “general” and two “roadside” stations). The bar graph indicates that the roadside station along the Nikko Kaido in Adachi Ward recorded daily-averaged values that exceeded 35 µg/m3 on approximately 160 days during FY 2000. This decreased to only about 10 days during both FY 2009 and 2010.

    However, much of Tokyo appears to be struggling to drop under the yearly limit of 15 µg/m3, and the data presented here are insufficient to definitively link the improvements directly to the actions of Ishihara and the Tokyo Metropolitan Government. A recent study has noted that mortality from cancer has decreased in Tokyo over the same period, but the methods available and the nature of the data prevent statistical attribution of any observed changes.

    Now, concentrations have begun to increase since the 3/11 disaster, but with only 10 years of data in total, and only 1 following the quake, it is impossible to attribute the changes to any particular cause. The magnitude of the change is also within the inter-annual variability (for example the increase from 2004 to 2005).

    Could this reflect the increased usage of traditional fuels for electrical generation with a number of nuclear plants offline?

    *Fiscal years in Japan begin in April, so FY2011 was from 4/1/2011 until 3/31/2012.

    An example of the raw data available from the Metropolitan Government with daily, monthly, and yearly averages.

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