A number of people lately have asked if ozone can get into your house through the swamp cooler. The answer is yes.

Four years ago, Dave Frank, a professor at California State University, Fresno, sampled the air in his own house -- which was cooled by swamp coolers -- and found the ozone levels inside were similar to the levels outside.

Ozone is the corrosive gas that makes smog dangerous. On hot, still days -- like the ones we're having now -- the sun cooks pollutants from cars and other sources into plumes of ozone, which attack living tissue, such as skin, eyes, throat and lungs.

A swamp cooler pulls air from the outside and passes it through water-cooled pads into the home. A modern air conditioner recirculates air already inside the house.

Ozone is a reactive gas that easily breaks apart when it comes in contact with firm surfaces. So after knocking around the house and recirculating in the air conditioner, most ozone in the house is gone, the professor said.

Bottom line: The professor told me he replaced his old swamp coolers with modern air conditioners.