"An AQI value of 100 generally corresponds to the national air quality standard for the pollutant, which is the level EPA has set to protect public health," says the Air Quality Index. "AQI values below 100 are generally thought of as satisfactory. When AQI values are above 100, air quality is considered to be unhealthy-at first for certain sensitive groups of people, then for everyone as AQI values get higher."
An "unhealthy" ranking is determined when the AQI is 150 to 200. That means everyone may begin to experience some adverse health effects, and members of the sensitive groups may experience more serious effects.
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