Action days are usually called when the AQI gets into the unhealthy ranges. Different air pollution control agencies call them at different levels. In some places, action days are called when the AQI is forecast to be Unhealthy for Sensitive Groups, or Code Orange. In this case, the groups that are sensitive to the pollutant should reduce exposure by reducing prolonged or heavy exertion outdoors. For ozone this includes: children and adults who are active outdoors, and people with lung disease, such as asthma. For particle pollution this includes: people with heart or lung disease, older adults and children. Occasionally, an action day is declared when the AQI is Moderate, or Code Yellow, if the levels are expected to approach Code Orange levels.
In many places, action days are called when the AQI is forecast to be Unhealthy, or Code Red. In this case, everyone should reduce exposure to air pollution, but especially the members of the sensitive group for the particular pollutant. What You Can Do.