In 1997, when the EPA announced the number
of counties that violated the new 8-hour ozone standard, it only
identified those counties that violated the standard and also
had monitors located in them. The counties identified by the
EPA that violated either the 8-hour ozone
or PM-2.5 standards can be reviewed.
For the 8-hour ozone standard, the EPA estimated that 280 counties
(with monitors) would violate the ozone standard. EPA historically
has also placed counties into nonattainment that do not have
monitors and are thought to contribute to a violation area. Thus,
the estimates originally announced by the Agency are much lower
than the 474 counties that the Agency announced on April 15,
2004 that are in nonattainment for the 8-hour ozone standard.
The most current estimate of the number of counties that violated
the PM-2.5 standard can be found in the EPA's latest trend report.
A summary of that information can be found elsewhere on this