A bubble of stagnant air bred from hot weather and car exhaust is expected to blow into southern Maine today.

The National Weather Service and the Maine Department of Environmental Protection issued a health warning for Maine’s coastal areas from Reid State Park south.

The areas ringing the coast, from Downeast Maine south through Bangor and Lewiston, are forecast to have moderate risks for high ozone levels. Northern Maine and the western mountain regions are forecast to have good air quality.

The warning advises people with heart and respiratory diseases, children and the elderly to limit their outdoor activities during the daylight hours.

The culprit is a bubble of ozone borne on winds from the southwest.

Cars and hot dry air cause a photochemical reaction, said Jim Hayes, a meterologist at the National Weather Service. Normally breathable oxygen gets turned into ozone.

“Ozone in the atmosphere is a good thing, but it can cause problems near the surface,” Hayes said.”It really needs the heat on the ground to become a problem. Then it depends on direction of the winds. These happen to be blowing our way.”