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A Decent Proposal? EPA's New Clean Air Standards
Kathryn S. Brown Abstract
In July 1997, the EPA will issue new air quality standards for ozone and fine particulate matter with a diameter of 2.5 microns or less (PM2.5) . Draft versions, released in November 1996, have raised loud debate over the science behind the new standards and the toll that implementation will exact on states and industry. It is estimated that about half of all U.S. counties currently fail to meet one or both of the proposed new standards.
The EPA has proposed ozone standards of no more than 0.08 parts per million averaged over an eight-hour period, and PM2.5 standards of 50 micrograms per cubic meter daily and 15 micrograms per cubic meter annually.
Setting a new standard for ozone is relatively simple, but only relatively. A preponderance of chemical data point toward ozone causing short-term respiratory effects, so the question is how much ozone is too much. A problem arises in setting a standard that adheres to the Clean Air Act, which calls for air standards that protect public health with an adequate margin of safety, regardless of the cost of these standards. "Margin of safety" would appear to be a moot point when it comes to ozone, because scientists believe there is no level of ozone that can be breathed in that will not cause some negative health effects.
It is more complicated to devise a new standard for PM2.5. Particulate matter is a mix of solid and liquid particles carried through the air. Scientists know that PM2.5 causes health effects but they are uncertain about exactly how these effects happen. This uncertainty leads to questions over the wisdom of setting a PM2.5 standard. There is already a standard in place regulating particulate matter with a diameter of 10 microns or less (PM10) , but it is PM2.5, scientists say, that goes deepest into the lungs and causes the most damage.
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