How It’s Used Ozone (aka trioxygen) is a colorless to bluish gas that condenses to a dark blue liquid, or blue-black crystals. Its characteristic odor is said by some to be reminiscent of chlorine, and as such is detectable at concentrations as low as 10 parts-per-billion. However the nose rapidly loses its ability to detect … Continue reading Ozone—and Ozone Monitoring Instrumentation