The United States Environmental Protection Agency (EPA) has promulgated a more stringent set of national ambient air quality standards (NAAQS) for ozone and particulate matter, which took effect September 16, 1997. Each state is required to prepare, and submit to EPA for approval, a state implementation plan (SIP) to regulate air emissions to ensure attainment and maintenance of air quality that meets or exceeds the NAAQS.
The prior standard for ozone was 0.12 parts per million (ppm) of ozone in the ambient air, based on a one-hour averaging period. The new ozone NAAQS is 0.08 ppm, based on an eight-hour averaging period. An area may be designated as "nonattainment" for the new ozone standard based on two criteria: (1) if the fourth highest eight-hour average concentration in a year exceeds 0.08 ppm and (2) if the fourth-highest concentrations each year for three consecutive years are averaged and exceed 0.08 ppm.
EPA has also revised the particulate matter NAAQS. The prior particulate matter standard was 150 micrograms per cubic meter (5g/m3) of particles with a nominal diameter of 10 microns or less (PM10), averaged over 24 hours. In addition, the prior standard called for PM10 concentrations not to exceed 50 5g/m3, averaged over a one-year period. The annual PM10 standard has been replaced by a new standard based on particulate matter with a nominal diameter of 2.5 microns or less (PM2.5). The new PM2.5 standard is 15 5g/m3 annual average, based on the three-year average of annual arithmetic mean PM2.5 concentrations. A new 24-hour PM2.5 standard has been set at 65 5g/m3. An exceedance of the new 24-hour PM2.5 standard occurs when the three-year average of the 98th percentile of 24-hour PM2.5 concentrations exceeds 65 5g/m3. The prior 24 hour PM10 standard of 150 Fg/m3 was revised so that compliance is determined by the 99th percentile of 24-hour concentrations.
62 Fed. Reg. 38652 (July 18, 1997) and 62 Fed. Reg. 38856 (July 18, 1997).
This article was prepared by S. Lee Johnson, a partner in our Environmental Department, and previously appeared in the September 1997 edition of Michigan Environmental Compliance, a monthly newsletter written by Honigman Miller Schwartz and Cohn on environmental regulatory developments in Michigan and published by M. Lee Smith Publishers. To subscribe, contact the publisher by either phone at 1-800-274-6675; email at custserv@mleesmith.com; the internet at http://www.mleesmith.com; or by mail at M. Lee Smith Publishers LLC, 5201 Virginia Way, P.O. Box 5094, Brentwood, TN 37024-5094.