Due to relatively low ozone levels during the last few years, only 19 percent of the nation's metropolitan areas violate EPA's current eight-hour ozone standard of 85 parts per billion, down from 40 percent just a few years ago. Non-metropolitan counties — those that include only rural areas or smaller cities — are in even better shape, with only a four-percent violation rate. Absent a tougher standard, this would have meant that many areas would shortly be getting out from under some of the Clean Air Act's most odious requirements.
With the new standard, however, non-attainment will become the norm, rather than the exception. EPA is proposing a standard somewhere in the range of 70–75 ppb. Based on current ozone levels, this would put 67–87 percent of metropolitan areas in violation, and 39–72 percent of non-metropolitan counties.