Ozone vacuum-ultraviolet (VUV) ozone generators, employ a light source that generates a narrow-band ultraviolet light, a subset of that produced by the Sun. The Sun's UV sustains the ozone layer in the stratosphere of Earth. UV ozone generators use ambient air for ozone production, no air prep systems are used (air dryer or oxygen concentrator), therefore these generators tend to be less expensive. However UV ozone generators usually produce ozone with a concentration of about 0.5% or lower which limits the potential ozone production rate. Another disadvantage of this method is that it requires the ambient air (oxygen) to be exposed
Exposing Microorganisms in the Stratosphere stratosphere (31 km above sea level), 99.9% of the entire population was destroyed. According to the researchers, "most terrestrial bacteria would be inactivated within the first [day] on Mars if contaminated spacecraft surfaces receive direct sunlight." Of the 40 million spores exposed to the stratosphere, only 267 spores (or 0.0007%) remained viable. Extrapolating this, no viable spores would remain if flight samples had an additional 150 minutes of Sun exposure in the stratosphere (630 min total time). The survivors showed three single nucleotide (base pair) substitutions compared to unexposed controls kept on the ground. These three coding regions are associated