Ozone is one of the six common air pollutants identified by the EPA as being critical to assessing environmental health of a place. Ozone occurs naturally in the stratosphere to provide a protective layer which filters the sun’s harmful ultraviolet rays. However, at the ground-level, ozone is created by a chemical reaction between nitrogen oxides and volatile organic compounds. Sunlight and heat cause ground-level ozone to form in harmful concentrations. Since nitrogen oxides come from internal combustion engines and volatile organic compounds come from vehicle exhaust, industrial emissions, gasoline vapors and chemical solvents, ground-level ozone is more prevalent in urban centers as oppose to rural areas. Ozone exposure is known to increase susceptibility to respiratory infections. (Greater Phoenix Regional Atlas: A Preview of the Region’s 50-year Future p. 40-41).
Data show the estimated exceedances of the standard (0.075 ppm) for an 8-hour average. Estimated exceedances are derived from the number of actual exceedances and the frequency of monitor reporting. These data include exceptional events, which is defined as an event that affects air quality, is not reasonably controllable or preventable, is an event caused by human activity that is unlikely to recur at a particular location or a natural event, and is determined by the EPA in accordance with 40CFR 50.14 to be an exceptional event. Although exceptional events may not be used by the EPA in determining nonattainment status, they contribute to poor environmental health.
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.
Readers are cautioned not to infer a qualitative ranking order of geographic areas based on AirData reports. Air pollution levels measured in the vicinity of a particular monitoring site may not be representative of the prevailing air quality of a county or urban area. Pollutants emitted from a particular source may have little impact on the immediate geographic area, and the amount of pollutants emitted does not indicate whether the source is complying with applicable regulations.
Disclaimer: AirData reports are produced from a direct query of the AQS Data Mart. The data represent the best and most recent information available to EPA from state agencies. However, some values may be absent due to incomplete reporting, and some values may change due to quality assurance activities. The AQS database is updated daily by state, local, and tribal organizations who own and submit the data. Please contact the appropriate air quality monitoring agency to report any data problems.
Data were collected from the U.S. Environmental Protection Agency's Monitor Values Report.
The source of ozone day data is http://www.epa.gov/airdata/ad_viz_ozcompare.html