Air Quality Index

The Air Quality Index (AQI) is a tool for reporting daily air quality. It tells you how clean or polluted the air is and what associated health concerns you should be aware of. The AQI focuses on health effects that can happen within a few hours or days after breathing polluted air. The AQI is reported for five major air pollutants regulated by the Clean Air Act: ground-level ozone, particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide. Useful health information about daily air quality, including near real-time AQI values for continuous ozone and particulate matter monitors, is available via the MIair web page. 

The Environmental Protection Agency has revised the AQI breakpoints to reflect recent changes to the National Ambient Air Quality Standards for ground-level ozone and fine particulate matter (PM2.5). Currently, daily ozone concentrations above 0.070 ppm or fine particulate matter concentrations above 35.4 µg/m3 activate the "unhealthy for sensitive groups" category - known to some people as a "code orange" air quality day. When levels reach this category, people in sensitive groups--children, the elderly, people with heart and lung disease, or people who are active outdoors--may start to experience negative health symptoms. Because of this, they should lower their physical activity levels to reduce their exposure and take it easy. 

SOURCE: https://www.airnow.gov/aqi/aqi-basics/