In July 1997, the U.S. EPA announced a new National Ambient Air Quality Standard for ground-level ozone. The EPA is phasing out and replacing the previous one-hour standard with a new eight-hour standard to protect public health against longer exposure to the air pollutant. A community will meet the new standard when the three-year average of the fourth-highest daily maximum eight-hour concentration measured at each monitoring site is less than 85 parts per billion.
The previous one-hour standard still applies to communities that were not in attainment of that standard in July 1997. Once these communities meet the one-hour standard, the EPA will judge them by the new eight-hour standard.
The EPA will use the eight-hour standard to judge the air quality of all other communities and will announce which ones are not in attainment of the new standard in 2000. Its decision will be based upon measurements taken during the three-year period from 1997 through 1999.
In July 1997, the U.S. EPA announced a new National Ambient Air Quality Standard for particulate matter (PM). EPA revised the primary (health-based) PM standards by adding a new annual PM2.5 standard set at 15 micrograms per cubic meter (µg/m3) and a new 24-hour PM2.5 standard set at 65 µg/m3. The annual PM10 standard of 50 µg/m3 was maintained and the PM10 24-hour standard of 150 µg/m3 was addjusted by changing the form of the standard. EPA is revised the secondary (welfare-based) standards by making them identical to the primary standards.
More Information about New NAAQS Standards
EPA'S Updated Air Quality Standards for Smog (Ozone) and Particulate Matter