The Dobson Unit is the most common unit for measuring ozone concentration.

The formation of patina on copper is similar to the formation of rust on iron. Both happen when oxygen in the air interacts with the metal atoms in the presence of water. Copper reacts with oxygen that is in the air, resulting in copper dioxideAs copper experiences natural or human-induced corrosive attack, its color changes from the iridescent, golden red normally associated with pure copper to a deep brown and, finally, to hues of blue and green.