Ozone action days happen when the ground level ozone becomes hazardous to your health. In essence, this means you should try not to breath. Certainly, do not suggest that your kids go outside and play. More people die from air pollution than guns… way more. Please do not pull the trigger.
Here is an example from June 17, 2014 issued by Pennsylvania Department of Environmental Protection:
Ozone Action Warning:
Air Quality Index (AQI)
106
Unhealthy for Sensitive Groups
Health Message: Active children and adults, and people with lung disease, such as asthma, should reduce prolonged or heavy exertion outdoors.
ACTION DAY
Forecast Discussion: Tuesday will be an Air Quality Action day for ozone for the Philadelphia metropolitan area. Full sun all afternoon, along with temperatures rising into the 90s °F, will promote ozone formation. An Appalachian lee trough will form east of I-95, which will be a focus for pollutant accumulation. Warm air arriving aloft will limit mixing. As a result of these factors, ozone will increase into the Code Orange range. Rising humidity and westerly transport aloft from the Ohio River Valley will increase particles into the mid-Moderate range. **Extended Forecast: Wednesday will be hotter and more humid, but stronger winds in the afternoon and the chance for convection in advance of a slowly moving cold front will limit ozone to the upper Moderate range. Particles will remain in the mid-Moderate range. The cold front will slowly move through the area on Thursday. Temperatures will decrease, although it will remain humid. Thunderstorms forming in the afternoon will limit both ozone and particles to the low Moderate range. -Huff/Catena/Ryan