Percent of Stations with Ozone Exceedance in Maricopa County by Region
One exceedence is recorded if the 4th-highest daily maximum value is above the level of the standard (0.075 ppm) for an eight hour average. In March 2008 EPA strengthened the ozone 8-hour standard. The 2008 standard applies retroactively to monitoring data for prior years. Some locations that previously met the ozone standard may exceed the level of the 2008 standard.