EPA scientists recommend tougher soot standards

The latest science supports substantially tightening U.S. EPA's air quality standards for soot in order to safeguard public health and the environment, according to a draft report from agency scientists.

Current evidence "calls into question whether the current suite" of health-based standards for fine particulate matter, or soot, "protects public health with an adequate margin of safety from effects associated with long- and short-term exposures," says the draft report issued this month.

EPA last revised its soot standard in 2006 under the George W. Bush administration, when the agency tightened the allowable concentrations of fine particulate matter from 65 micrograms per cubic meter to 35 micrograms when measured over a 24-hour period. EPA also opted to retain the annual soot standard at 15 micrograms per cubic meter, even though EPA's staff and scientific advisers had recommended a standard between 13 and 14 micrograms. EPA set an identical welfare-based standard at 15 micrograms.

A federal appeals court last year sent the annual standard back to EPA for review, finding that the Bush administration's standards were, "in several respects, contrary to law and unsupported by adequately reasoned decisionmaking" (Greenwire, Feb. 24, 2009).

The court sided with environmental and public health groups that had sued the agency, saying EPA failed to adequately explain why a health-based annual level of 15 micrograms per cubic meter is sufficient to protect the public health and why the same level was sufficient to protect public welfare and guard against visibility impairment. The court left the annual standards in place while EPA reconsiders the rule.


Fine particle pollution can lodge deep in the lungs and cause serious health problems. Numerous scientific studies have linked exposure to particle pollution to respiratory problems, asthma, bronchitis, heart attacks and other problems. Fine particles are also the major cause of reduced visibility, or haze, in parts of the United States, including many parks and wilderness areas.

EPA will address the court's concerns in its periodic review of air quality standards for soot. EPA plans to issue its draft proposal in November and issue a final rule in July 2011, according to the agency's fall 2009 rulemaking agenda.

In the draft report, the EPA staff suggests that the agency consider setting the annual and 24-hour standards so that the annual standard would provide long-term protection against long- and short-term exposures in conjunction with a tighter 24-hour standard to protect against high peak concentrations.

The report suggests two ranges to provide such protections that involve tightening the annual standard. One would tighten the annual standard to between 12 and 13 micrograms per cubic meter while either retaining or revising the 24-hour standard in a range of 30 to 35 micrograms.

The second scenario would involve tightening the annual standard to between 10 and 11 micrograms per cubic meter, coupled with lowering the 24-hour standard within a range of 25 to 30 micrograms.

EPA staff also reached the preliminary conclusion that the available data calls into question the adequacy of the agency's current welfare-based standards that aim in part to protect visibility. The draft assessment urges EPA to consider alternative standards to provide further protection, particularly in urban areas.

Frank O'Donnell, president of the advocacy group Clean Air Watch, welcomed the draft report. "The agency's own experts argue that the science calls for much stricter limits on the public's annual exposure to deadly particle soot," O'Donnell said. "This could have big implications for some of the major sources of fine particle soot, especially coal burning and diesel engines."

O'Donnell added that the EPA staff recommendations are noteworthy because there have been preliminary indications that the Obama EPA is inclined to adopt its scientific advisers' recommendations. "They may not go to the lowest end of it, but they want to respect what the science advisers are putting forward," he said.

Howard Feldman, director of regulatory and scientific affairs at the American Petroleum Institute, declined to comment on the details of the recommendations, saying that his group would need to look at which studies the EPA staff used to reach its conclusions. There have been a host of new studies since the last review, he said, some of which support tighter standards and others that do not. API opposed the 2006 soot standards, calling the decision "overly conservative" and "based on incomplete science."

Feldman also noted that a recent EPA report detailing air quality trends showed that U.S. particulate pollution measured annually fell by 19 percent between 1990 and 2008 (E&ENews PM, March 10). "We as a society have been making progress and will continue to make progress," he said.

Click here to read the draft staff report.

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