On September 21, 2006, the United Stated Environmental Protection Agency (EPA) revised theNational Ambient Air Quality Standards (NAAQS) for both fine and inhalable particulate matter.The EPA lowered the 24-hour standard for fine particulate matter, consisting of particles that are2.5 microns or smaller (PM2.5), from 65 micrograms per cubic meter (μg/m~3) to 35 μg/m~3, andretained the current annual fine particle standard of 15 μg/m~3. The EPA decided to retain theexisting 24-hour standard of 150 μg/m~3 for coarse particulate matter, those particles equal to orless than 10 microns (PM10). Stating a lack of evidence linking health problems to long-termexposure to coarse particle pollution, the EPA revoked the annual PM10 standard.According to the EPA, the agency evaluated thousands of peer-reviewed scientific studies aboutthe effects of particle pollution on public health and welfare prior to selecting these specificstandards. The process included public hearings and written comment periods. The EPAsubjected its science and policy review documents to external scientific review. However, thedecision has disappointed the environmental, medical, and scientific communities. Manyenvironmental watch dog groups and environmental professionals supported lower standards,claiming recent health studies support their positions.But who's right? This paper presents an unbiased look at the revised NAAQS.
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