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
Exposing Microorganisms in the Stratosphere Exposing Microorganisms in the Stratosphere Exposing Microorganisms in the Stratosphere (E-MIST) is a NASA study to determine if a specific microorganism could survive conditions like those on the planet Mars. The study transported "Bacillus pumilus" bacteria and their spores by helium-filled balloon to the stratosphere of Earth (~31 km above sea level) and monitored the ability of the microorganisms to survive in extreme Martian-like conditions such as low pressure, dryness, cold, and ionizing radiation. A test flight of the balloon and gondola was launched from New Mexico on 24 August 2014. A second, longer flight, took place on 10 October