What is the Air Quality Index, a High Pollution Advisory and a Health Watch?
Local air quality affects how you live and breathe. Like the weather, it can change from day to day or even hour to hour. The Maricopa County Air Quality Department (MCAQD) along with the Environmental Protection Agency (EPA) and Arizona Department of Environmental Quality (ADEQ) have been working to make information about outdoor air quality as easy to find and understand as weather forecasts.
A key tool in this effort is the Air Quality Index, or AQI. MCAQD uses the AQI to provide simple information about air quality in Maricopa County, how unhealthy air may affect you, and how you can protect your health.
The AQI is an index for reporting daily air quality. It displays how clean or unhealthy the air is, and what associated health effects might be a concern. The AQI focuses on health effects one may experience within a few hours or days after breathing unhealthy air. The AQI is calculated for air pollutants regulated by the Clean Air Act: such as ground level ozone, particulate matter (PM) pollution, such as PM 10 (dust) or PM2.5 (smoke) and carbon monoxide.
The EPA has established national air quality standards for each of these pollutants to protect public health.
Think of the AQI as a yardstick that runs from 0 to 500. The higher the AQI value, the greater the level of air pollution and the greater the health concern. For example, an AQI value of 50 represents good air quality with little or no potential to affect public health.
An AQI value of 100 generally corresponds to the federal health standard for the pollutant, which is the level EPA has set to protect public health. AQI values at or 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 increase.
If the concentration levels for ozone, PM10 and PM2.5 are expected to approach the federal health standard then a health watch will be called. If those levels are expected to surpass the federal health standard then a high pollution advisory (HPA) will be in effect.
Unusually sensitive people should consider reducing prolonged or heavy outdoor exertion during a health watch.
Children, adults and people with lung disease such as asthma should reduce prolonged or heavy outdoor exertion. Maricopa County employers enlisted in the Travel Reduction Program are asked to activate their HPA plans on high pollution advisory days.