Measuring Air Pollutants
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| The 1990 amendments to the federal Clean Air Act set guidelines for U.S. air quality. Air is monitored in cities across the nation for "criteria pollutants": lead, ozone (O3), carbon monoxide (CO), sulfur dioxide (SO2), nitrogen oxides (NOx), and particulate matter, as well as for toxic hydrocarbons. Pollutants are measured in parts per million (ppm) of air. For example, if 50 molecules of CO are detected in a volume of air containing 1 million molecules, the CO reading would be 50 parts per million. |
Figure 3
Air monitoring station Rapid City, South Dakota |
