NCPA - National Center for Policy Analysis

PM 2.5 Problems Just Hot Air

October 9, 2003

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 powerplant emissions -- has been greatly overstated, says Ben Lieberman. He disagrees with the claim by the Environmental Protection Agency 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.
  • Neither study singles out PM 2.5 as the clear culprit, as sulfur 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 behavior -- 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.


Browse more articles on Environment Issues