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Air Quality Indicator: Daily Ozone Levels Measure: Number of days with Ozone levels over National Ambient Air Quality Standards (NAAQS).
Ozone is a gas that you cannot see or smell. "Good" ozone occurs naturally in the sky about 10 to 30 miles above the earth's surface. It forms a layer that protects life on earth from the sun's harmful rays. Ground-level ozone, or “bad” ozone, forms when precursor pollutants that come from cars, power plants, and other sources come in contact with each other in heat and sunlight. It is the biggest part of what is we call “smog.”
Ground-level ozone is bad for your health and the environment. Studies have shown that being exposed to bad ozone can cause respiratory symptoms like coughing or pain when you take a deep breath, make asthma worse, cause lungs to get inflamed and temporarily decrease the lung capacity of healthy adults. Repeated contact with bad ozone may permanently scar lung tissue.
Because sunlight and heat cause ozone to form, ozone levels are monitored only during warmer times of the year. The length of the ozone season varies between different regions in the United States. In Oregon, the ozone monitoring season lasts from May 1 to September 30.
Both nitrogen oxides and volatile organic compounds are emitted by cars, trucks, power plants and factories. Thus high ozone levels are usually observed downwind of densely populated cities, causing ozone monitoring to be focused on urban and industrial areas. Between 1997 and 2007, ozone measurements were available for eight Oregon counties: Clackamas, Columbia, Jackson, Lane, Linn, Marion, Multnomah and Umatilla.
The tables below show the proportion of days during which the measured ozone concentration was higher than the National Ambient Air Quality Standards (NAAQS) of 80 parts per billion. This indicator can be interpreted as the number of days that ozone levels were unhealthy for sensitive populations. A long-term (annual average) indicator for ozone was not included because most studies have focused on short-term effects. Ozone NAAQS exceedances were very rare; in most years, exceedances did not occur in any county. The highest numbers of days with exceedances were observed in 1998, with five days in Jackson County and three days in Clackamas County.
Table 1: Number of days during which ozone concentrations exceeded the NAQQS of 0.08 mcg/m3, by county.
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Table 1: Number of days during which ozone concentrations exceeded the NAQQS of 0.08 mcg/m3, by county. (No data were available for counties not shown here. Empty table cells also indicate missing data.)
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Table 2: Number of person-days (in thousands) during which 8-hour average ozone concentrations exceeded the NAAQS of 0.08 mcg/m3 by county.
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Table 3: Number of days during which ozone concentrations exceeded the NAQQS of 0.08 mcg/m3, by Metropolitan Statistical Area (MSA).
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Table 4: Number of person-days (in thousands) during which 8-hour average ozone concentrations exceeded the NAQQS of 0.08 mcg/m3, by Metropolitan Statistical Area.
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