Are Small Particles Such a Big Problem?

According to the Environmental Protection Agency, small particles in the air pose the greatest threat that it or any other regulatory agency is currently addressing. A host of major rules currently control this pollutant and many more are in the works. The claimed benefits of these measures outweigh virtually all other benefits of the regulatory state combined. Nonetheless, the evidence strongly suggests that the problem posed by these particles has been greatly overstated.<?xml:namespace prefix = o ns = “urn:schemas-microsoft-com:office:office” />


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In a recent report to Congress, the Office of Management and Budget (OMB) compiled the agency-reported costs and benefits of all major federal rules since 1992. OMB found that “four EPA rules . . . account for a substantial fraction of the aggregate benefits.” [1] All four are rules targeting airborne particulate matter (PM), especially those particles 2.5 micrometers or less in diameter (PM 2.5). The agency's estimated benefits for these rules range from $96 to $113 billion per year. [2] Amazingly, this compares to only $38 to $104 billion in combined benefits for all 103 other major rules coming from the Departments of Agriculture, Education, Energy, Health & Human Services, Housing & Urban Development, Labor, and Transportation, as well as the rest of EPA. [3]


These four rules, three dealing with PM 2.5 from motor vehicle tailpipe emissions and one targeting power plant emissions, claim most of their extraordinary benefits by preventing tens of thousands of PM 2.5-induced deaths.


Additional measures are in the pipeline that will crack down further on PM 2.5 from combustion sources. EPA's 1997 National Ambient Air Quality Standard (NAAQS) for PM 2.5, after being held up by legal challenges, will begin to be implemented in 2004. [4] This rule, one of the most expensive in the history of the Clean Air Act, will require state and local governments across the nation to keep ambient PM 2.5 levels within acceptable limits. The Bush administration is also in the process of setting tougher emissions controls for non-road diesel engines such as those used in construction equipment. [5] Like the other rules targeting PM 2.5, EPA is claiming massive potential gains – as much as 9,600 lives saved each year and up to $81 billion in benefits. [6]


In addition, the administration's proposed Clear Skies Act, introduced in the Senate by Sen. James Inhofe (R-OK), claims to save yet another 14,100 lives and accrue up to $110 billion in annual health benefits. [7] These benefits, calculated by EPA, come mostly from further PM 2.5 reductions from power plants. Senate Democrats have introduced alternative versions that claim even greater results.


The cumulative estimated benefits of reducing PM 2.5 from these current and proposed future measures approaches half a trillion dollars annually. And these are just for post-1990 rules–previous measures had already brought down particulate matter levels significantly since their highs in the middle 20th century. [8]


If true, PM 2.5 reductions are far and away the most important regulatory endeavor being undertaken. In contrast, the Department of Transportation's efforts to improve the safety of our highways and skyways are downright insignificant, with benefits from major rules estimated at less than $10 billion dollars annually. [9] Likewise, agencies like the Department of Labor, with total annual regulatory benefits of $1.8 to $4.2 billion, or Agriculture with its $3.1 to $6.2 billion, seem trivial in comparison with EPA's PM 2.5 agenda. [10]


EPA concedes costs as well as benefits in fighting PM 2.5. These rules have increased the price consumers pay for energy, as well the cost of motor vehicles and other goods. But the costs, though high, are only a small fraction of the claimed benefits, and thus get relatively little attention.


The magnitude of these alleged benefits stands in stark contrast with the scant evidence supporting them. Surprisingly, EPA's PM 2.5 crusade is largely based on two epidemiologic studies, the Harvard Six Cities Study and American Cancer Society Study. [11] Both show a correlation between PM 2.5 exposure and mortality. In other words, mortality was found to be somewhat higher in those areas where estimated PM 2.5 exposures were higher. Based on the association found in these studies, EPA then estimates the number of lives and dollars saved by each of its measures to reduce PM 2.5 from utilities, vehicles, or other sources.


But both studies have serious flaws, and exemplify why it is risky to base policy on epidemiologic evidence alone. For one thing, 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. In addition, 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. For example, four of the cities in the Six Cities Study showed no association between PM 2.5 and increased mortality, and the American Cancer Society study found no association for those persons with more than a high school education or for women. These and many other unexplainable inconsistencies strongly suggest 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. However, other published studies that are at least as credible have found no association between current PM 2.5 levels and mortality. For example, an extensive long-term study of a large population of veterans found no increase in mortality associated with PM 2.5 exposures.[1][12] These results add further support to the proposition that any relationship between current PM 2.5 levels and mortality is very weak and possibly nonexistent.


The scientific debate has recently been reignited at EPA, as the agency is currently reviewing the PM 2.5 NAAQS. But thus far, the agency has shown no signs of changing its views, and has even suggested that it may need to tighten the current standard to further protect the public health from PM 2.5.


Given all the current measures and potential new ones, EPA's efforts to reduce PM 2.5 will continue to be either the federal government's biggest regulatory success, or its biggest regulatory boondoggle, for many years to come.


[1]1 OMB, “Draft 2003 Report to Congress on the Costs and Benefits of Federal Regulations: Notice,” 68 Fed. Reg. 5,492, 5,493 (February 3, 2003).

2 <?xml:namespace prefix = st1 ns = “urn:schemas-microsoft-com:office:smarttags” />Id. at 5,493.

3 Id. at 5,494.

4 EPA, “National Ambient Air Quality Standards for Particulate Matter: Final Rule,” 62 Fed. Reg. 38,652 (July 18, 1997).

5 EPA, “Control of Emissions of Air Pollution from Non-road Diesel Engines and Fuel: Proposed Rule,” 68 Fed. Reg. 28,328 (May 23, 2003).

6 EPA Regulatory Announcement, “Public Health and Environmental Benefits of EPA's Proposed Program for Low-Emission Non-road Diesel Engines and Fuel,” April 2003.

7 EPA, “Clear Skies: Human Health and Environmental Benefits,” at

8 Indur Goklany, “Clearing the Air: The Real Story of the War on Air Pollution, pp. 80-82 (Washington, DC: Cato Institute, 1999).

9 OMB, 68 Fed. Reg. at 5494, Table 2.

10 Id.

11 Douglas W. Dockery, et al., “An Association Between Air Pollution and Mortality in Six U.S. Cities,” New England Journal of Medicine, vol. 329 (1993), pp. 1753-1759; C. A. Pope et al., “Particulate Air Pollution as a Predictor of Mortality in a Prospective Study of U.S. Adults,” American Journal of Respiratory Critical Care Medicine, vol. 151 (1995), pp. 669-674.

12 F.W. Lipfert et al., “The Washington University-EPRI Veterans' Cohort Mortality Study,” Inhalation Toxicology, vol. 12, supp. 4 (2000), pp. 41-73.