Vapor-compression refrigeration replaced, such as sulfur dioxide. Haloalkanes are also an order(s) of magnitude more expensive than petroleum derived flammable alkanes of similar or better cooling performance. Unfortunately, chlorine- and fluorine-bearing refrigerants reach the upper atmosphere when they escape. In the stratosphere, CFCs break up due to UV radiation, releasing their chlorine free radicals. These chlorine free radicals act as catalysts in the breakdown of ozone through chain reactions. One CFC molecule can cause thousands of ozone molecules to break down. This causes severe damage to the ozone layer that shields the Earth's surface from the Sun's strong UV radiation, and has
S/2004 S 6 dissipate on a timescale of years or months. Notably, an imaging sequence covering an entire orbital period at 4 km resolution taken on November 15, 2004 (soon after 's discovery) failed to recover the object, while it has been seen again later. The lighting conditions in 's part of the orbit were different during these two observations, however, with the discovery being made when the region was strongly backlit by the sun. A suggested resolution of the absence in November is that 's visibility is primarily due to a diffuse cloud of fine dust that is much brighter in forward