Danger of small particle pollution overstated

The problem posed by airborne particulate matter (PM) – especially those particles 2.5 micrometers or less in diameter (PM 2.5) that are emitted from motor vehicle tailpipe and power-plant emissions – has been greatly overstated, says Ben Lieberman. He disagrees with the claim by the U.S. Environmental Protection Agency (EPA) that the aggregate benefits from fighting PM 2.5 save $96 to $113 billion per year.

The magnitude of these alleged benefits stands in stark contrast with the scant evidence supporting them, explains Lieberman:

  • EPA's PM 2.5 crusade is largely based on two epidemiologic studies, the Harvard Six Cities Study and American Cancer Society Study.

  • But both studies have serious flaws and exemplify why it is risky to base policy on epidemiologic evidence alone.

    According to Lieberman:

  • Neither study singles out PM 2.5 as the clear culprit, as sulphur dioxide and other pollutants whose concentrations are correlated with PM 2.5 have an equal or greater effect on mortality.

  • Also, the results are highly inconsistent in that the PM 2.5/mortality connection exists for some subsets of the population under study, but is completely absent for others; this suggests that so-called confounders –- extraneous factors like diet, exercise, and smoking behaviour – are really behind the findings.

    Both studies attempted to control for most (but not all) possible confounders, but doing so is quite difficult and the results indicate a failure to clearly isolate a significant PM 2.5 effect.

    Despite these deficiencies, the Harvard Six Cities and American Cancer Society Studies have become the "official science" relied upon by EPA in claiming massive benefits from its PM 2.5 agenda, says Lieberman.

    Source: Ben Lieberman, Are Small Particles Such a Big Problem? Competitive Enterprise Institute, September 26, 2003.

    For text http://www.cei.org/utils/printer.cfm?AID=3677
    For more on air pollution http://eteam.ncpa.org/policy/Air_Problems/Outdoor_Air/

    FMF Policy Bulletin/14 October 2003
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