National air quality has improved since the 1990's, but many challenges remain in protecting public health and the environment from air quality problems. Federal, state, local, and tribal air agencies operate and maintain a wide variety of outdoor air monitoring systems across the United States. Many of these systems serve several environmental purposes. At a basic level, they let us know how clean or polluted the air is, help us track progress in reducing air pollution, and share information with the public about air quality in their communities through the Air Quality Index (AQI). The AQI is a tool to help you quickly learn when air pollution is likely to reach unhealthy levels.
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