Federal environmental officials say the hot and humid weather is expected to produce poor air quality in southern Connecticut, coastal Rhode Island and southeastern Massachusetts.
The Environmental Protection Agency says ground-level ozone is expected Wednesday. It can cause breathing problems and aggravate asthma and other pre-existing lung diseases and increase the risk of respiratory infection.
Strenuous outdoor activity should be avoided, particularly among children and adults with respiratory problems.
Cars, trucks and buses give off most of the pollution that creates ozone. Officials say gas stations and certain household products such paints and cleaners, lawn and garden equipment add to the ozone problem.