On Earth, these are serious problems, but would be positive factors on Mars. Further, PFCs don't have negative effects on living things. Building up an ozone layer in the air of Mars would be an important goal for terraformers. Mars has only a very tiny amount of ozone at present and it needs to be increased as a UV protector, Margarita says. Sunlight is absorbed by a planet's surface, which then radiates warming infrared energy into the atmosphere.
Greenhouse gases prevent that energy from escaping into space.
Sunlight arrives at a planet's surface mostly as visible and ultraviolet light. The planet absorbs this solar energy, and then radiates warming infrared energy back out into the air. Greenhouse gases in the air work as a layer of global insulation, trapping the infrared radiation and preventing it from escaping away into space. Carbon dioxide and water are good at trapping some of this infrared energy, but not all of it. On Earth, there's so much CO2 and water in the atmosphere that it doesn't matter if some of the infrared radiation escapes out into space.