Comparing Metro Phoenix
Ozone
Description: Ozone (O3) is one of the criteria air pollutants identified by the EPA as being critical to assessing the environmental health of a place. Heat and sunlight coupled with emissions yield unhealthy ozone levels. 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 from a chemical reaction between nitrogen oxides and volatile organic compounds. When these chemicals are exposed to sunlight and hot weather, they form ground-level ozone in harmful concentrations.
Rationale: Ozone is the primary component of smog. Its effects on human health include increasing lung sensitivity to other air pollutants and decreasing general lung function in otherwise healthy individuals. The 4th maximum 8-hour concentration levels are identified in the graphs. The National Standard is 0.08 parts per million (ppm). Areas with a 3-year average that exceeds the standard are considered to be in exceedance. Each of the cities has exceeded this standard during at least a single year. Cities located in nonattainment areas include Atlanta, Phoenix, Denver, Raleigh, and San Diego.
Source: Decision Center for a Desert City (DCDC) using records from the U.S. Environmental Protection Agency's Monitor Trends Report - Criteria Air Pollutants. For additional information on ozone pollution, refer to the EPA Greenbook, available online at: http://www.epa.gov/oar/oaqps/greenbk/o3co.html#Ozone8.
