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Ozone

Description: 

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 Source: 

Data were collected from the U.S. Environmental Protection Agency's Monitor Values Report.
Source: http://www.epa.gov/airdata/ad_rep_mon.html
The source of ozone day data is http://www.epa.gov/airdata/ad_viz_ozcompare.html

Data Quality Comments: 

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.

iconTotal Ozone Estimated Exceedances in Reporting Arizona Counties

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Visualization Notes:

Maricopa County has the highest number of ozone exceedances by a large margin over other counties in Arizona. This is a result of actual ozone exceedances along with the higher number of monitoring stations in Maricopa County. Hot, dry cities are especially prone to high levels of ozone, which is created when heat causes a chemical reaction between substances from vehicle exhaust and industrial emissions.

iconTotal Ozone Exceedances in Maricopa County by Region

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Visualization Notes:

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.

iconTotal Number of Ozone Days by County

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Visualization Notes:

This graph shows the number of days when any monitor in the county records an exceedance of the standard (0.075 ppm) for an 8-hour average. This measure helps to even out the discrepancy between counties with one or few monitors and those with many, such as Maricopa County.  Note that Maricopa County still shows the highest number of exceedance days, even when normalizing for the number of monitors.

Data Source

Data were collected from the U.S. Environmental Protection Agency's Monitor Values Report.
Source: http://www.epa.gov/airdata/ad_rep_mon.html
The source of ozone day data is http://www.epa.gov/airdata/ad_viz_ozcompare.html