A CFC is a gas that factories used to put in fridges, freezers, and spray cans. The letters stand for chlorofluorocarbon — a carbon compound with chlorine and fluorine. These gases were handy: they carried cold well and did not catch fire easily. Later, scientists showed they climb high and damage the ozone layer, the part of the sky that blocks a lot of the sun’s more harmful rays. Many countries then limited or banned them. In loose talk, “CFCs” can mean “those old fridge gases that hurt the ozone,” even when the speaker could not name the chemistry. Newer fridge gases are not exactly CFCs, though headlines sometimes lump them together.