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About the Air Quality Levels

AQI
Air Pollution Level
Health Implications
Cautionary Statement (for PM2.5)
0 to 50
Good
Air quality is considered satisfactory, and air pollution poses little or no risk
None
51 to 100
Moderate
Air quality is acceptable; however, for some pollutants there may be a moderate health concern for a very small number of people who are unusually sensitive to air pollution.
Active children and adults, and people with respiratory disease, such as asthma, should limit prolonged outdoor exertion.
101 to 150
Unhealthy for Sensitive Groups
Members of sensitive groups may experience health effects. The general public is not likely to be affected.
Active children and adults, and people with respiratory disease, such as asthma, should limit prolonged outdoor exertion.
151 to 200
Unhealthy
Everyone may begin to experience health effects; members of sensitive groups may experience more serious health effects
Active children and adults, and people with respiratory disease, such as asthma, should avoid prolonged outdoor exertion; everyone else, especially children, should limit prolonged outdoor exertion
201 to 300
Very Unhealthy
Health warnings of emergency conditions. The entire population is more likely to be affected.
Active children and adults, and people with respiratory disease, such as asthma, should avoid all outdoor exertion; everyone else, especially children, should limit outdoor exertion.
300+
Hazardous
Health alert: everyone may experience more serious health effects
Everyone should avoid all outdoor exertion

Five major pollutants

EPA establishes an AQI for five major air pollutants regulated by the Clean Air Act. Each of these pollutants has a national air quality standard set by EPA to protect public health:

  • ground-level ozone
  • particle pollution (also known as particulate matter, including PM2.5 and PM10)
  • carbon monoxide
  • sulfur dioxide
  • nitrogen dioxide

To know more about Air Quality and Pollution, check the wikipedia Air Quality topic.