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The Air Quality Index
The Air Quality Index (AQI) is an index for reporting daily air quality. It tells how clean or polluted your outdoor air is, and what associated health effects might be a concern for you. The AQI focuses on health affects you may experience within a few hours or days after breathing polluted air. EPA calculates the AQI for five major air pollutants regulated by the Clean Air Act: ground-level ozone, particle pollution (also known as particulate matter), carbon monoxide, sulfur dioxide, and nitrogen dioxide. For
About the Data
The air quality data used in these maps and to generate forecasts are collected using either federal reference or equivalent monitoring techniques or techniques approved by the state, local or tribal monitoring agencies. Since the information needed to make maps must be as "real-time" as possible, the data are displayed as soon as practical after the end of each hour. Although some preliminary data quality assessments are performed, the data as such are not fully verified and validated through the quality assurance procedures monitoring organizations use to officially submit and certify data on the EPA Air Quality System (AQS). Therefore, data are used on the AirNow website only for the purpose of reporting the AQI. Information on the AirNow website is not used to formulate or support regulation, guidance or any other agency decision or position.
(Source: http://airnow.gov/index.cfm?action=topics.about_airnow, accessed on 6-30-2010)
About Ground-level Ozone
Ozone (O3) is a gas composed of three oxygen atoms. It is not usually emitted directly into the air, but at ground level is created by a chemical reaction between oxides of nitrogen (NOx) and volatile organic compounds (VOC) in the presence of sunlight. Ozone has the same chemical structure whether it occurs miles above the earth or at ground level and can be "good" or "bad," depending on its location in the atmosphere.
In the earth's lower atmosphere, ground level ozone is considered "bad." Motor vehicle exhaust and industrial emissions, gasoline vapors, and chemical solvents, as well as natural sources, emit NOx and VOC that help form ozone. Ground level ozone is the primary constituent of smog. Sunlight and hot weather cause ground level ozone to form in harmful concentrations in the air. As a result, it is known as a summertime air pollutant. Many urban areas tend to have high levels of "bad" ozone, but even rural areas are also subject to increased ozone levels because wind carries ozone and pollutants that form it hundreds of miles away from their original sources.
"Good" ozone occurs naturally in the stratosphere approximately 10 to 30 miles above the earth's surface and forms a layer that protects life on earth from the sun's harmful rays.
(Source: http://www.epa.gov/air/ozonepollution/ accessed on 7/1/2010)
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