Other Regulatory Activity

摘要

On July 30, 2004 (69 FR 45592-5596), EPA issued a final rule revising 40 CFR Parts 50 and 58 to remove the 1997 national ambient air quality standards (NAAQS) for PM-10 (particulate matter with an aerodynamic diameter ≤ 10 microns). The 1997 PM-10 NAAQS was vacated in a May 14, 1999 decision by the U.S. Court of Appeals for the District of Columbia Circuit (DC Circuit Court) in American Trucking Associations, Inc. et al. v. EPA (175 F. 3d 1027). On July 18, 1997 (62 FR 38652), EPA issued new NAAQS for particulate matter. In issuing new NAAQS, EPA established new 65-μg/m~3 24-hour and 15-μg/m~3 annual-average limits for PM-2.5 (particulate matter with an aerodynamic diameter ≤ 2.5 microns) concentrations in ambient air. Compliance with the 24-hour PM-2.5 limit is based on the three-year average of the 98th percentile 24-hour average concentrations. Compliance with the annual standard is based on the three-year average of annual arithmetic mean concentrations. The PM-2.5 standard does not replace, but is in addition to, the PM-10 NAAQS.