The air we breathe is not always good for us. It often contains pollution, which can cause or aggravate a number of health issues including respiratory and cardiovascular diseases.

Under the Clean Air Act, the EPA is responsible for monitoring air pollution across the United States. Calculated on the Air Quality Index (AQI), a standardized indicator, the agency’s daily reports focus on the health effects people may suffer as a result of breathing polluted air. The scale runs from 0-500 with increasing AQI values correlating to higher levels of pollution and an escalating risk to public health. Values above 100 are considered unhealthy.

Unlike some other environmental challenges, air pollution is nearly impossible to avoid, as we all need to breathe. Caused mainly by vehicle exhaust, power generation, and industrial emissions, its sources are ubiquitous. The five major air pollutants measured on the AQI are, ground level ozone, particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide.

Pollutants often build to unsafe concentrations on days with very high temperatures and/or a lack of wind.  Ground level ozone, for example, forms when nitrogen oxides react with heat and U.V. light near the surface. Air quality alerts, therefore, are often issued in conjunction with heat advisories.