What are the Current National Ambient Air Quality Standards?
EPA has completed its reviews of the national air quality standards for ozone and particulate matter. The Administrator signed both the new particulate and ozone standards in July 1997. As a result of this review, EPA is phasing out and replacing the previous 1-hour primary ozone standard (health-based) with a new 8-hour standard to protect against longer exposure periods. In establishing the 8-hour standard, EPA is setting the standard at 0.08 parts per million (ppm) and defines the new standard as a “concentration-based” form, specifically the 3-year average of the annual 4th-highest daily maximum 8-hour ozone concentration. The standards were last revised in 1979. EPA is also revising the primary (health-based) PM standards by adding a new annual PM2.5 standard set at 15 micrograms per cubic meter (g/m3) and a new 24-hour PM2.5 standard set at 65 g/m3. EPA is retaining the annual PM10 standard of 50 g/m3 and adjusting the PM10 24-hour standard of 150 g/m3 by changing the form of the
