Air conditioning eventually reach the upper atmosphere. Once the refrigerant reaches the stratosphere, UV radiation from the Sun homolytically cleaves the chlorine-carbon bond, yielding a chlorine radical. These chlorine radicals catalyze the breakdown of ozone into diatomic oxygen, depleting the ozone layer that shields the Earth's surface from strong UV radiation. Each chlorine radical remains active as a catalyst until it binds with another radical, forming a stable molecule and quenching the chain reaction. Prior to 1994, most automotive air conditioning systems used R-12 as a refrigerant. It was replaced with R-134a refrigerant, which has no ozone depletion potential. Old R-12 systems
UV filter offer some protection against lens contamination while minimising the inherent additional distortion. However, in photography, the term "UV filter" can be also misused as a filter that passes UV light while blocking other wavelengths in the light spectrum, in the same way the term "IR filter" is also sometimes misused. The correct names for such filters though, are "UV pass filter" and "IR pass filter". This is a very specialized area in photography. Excessive UV radiation can expose humans to various risks, including skin diseases such as sunburns, photo-aging, and skin cancers. UV radiation can be classified as UVA (320-400