Ozone is a toxic, colorless gas (but can be blue when in high concentration) with a characteristic acrid odor. A variant of normal oxygen, it had three oxygen atoms per molecule rather than the usual two. Ozone strongly absorbs ultraviolet radiation at wavelengths of 220 through 290 nm with peak absorption at 260.4 nm. Ozone will also absorb infrared radiation at wavelengths in the range 9-10 μm. Ozone occurs naturally in the ozonosphere (ozone layer), which surrounds the earth, protecting living organisms at the earth's surface from ultraviolet radiation. The ozonosphere is located in the stratosphere from 6–31 miles (10–50 km) above the earth's surface, with the highest concentration between 7.5 and 12 miles (12 and 20 km). The concentration of ozone in the ozonosphere is 1 molecule per 100,000 molecules, or if the gas were at standard temperature and pressure, the ozone layer would be 0.12 inch (3 mm) thick. However, the ozone layer absorbs about 90% of incident ultraviolet radiation...