The Air Quality Index (AQI) is an index for reporting daily air quality. It measures how clean or polluted the outdoor air is and what associated health effects might be a concern. The Environmental Protection Agency (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 each of these pollutants, EPA has established national air quality standards to protect public health.
time period: current; refreshes every 5 minutes.
source:
http://www.epa.gov/airnow/today/airnow.kml
http://www.airnow.gov/index.cfm?action=google_earth.index
info: http://www.airnow.gov
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