Pursuant to a legislative requirement, GAO reviewed the Environmental Protection Agency's (EPA) two new rules on national ambient air quality standards. GAO found that: (1) the first rule would revise the National Ambient Air Quality Standards (NAAQS) for particulate matter (PM); (2) the second rule would revise the NAAQS for ozone; (3) EPA states that these revised standards will provide increased protection to the public, against a wide range of ozone-induced and PM-related health effects; (3) on July 18, 1997, a Petition for Review of these final rules was filed in the United States Court of Appeals; and (4) the plaintiffs contend that these rules violate the Clean Air Act and the Small Business Regulatory Enforcement Fairness Act of 1996.