In 1785, the Dutch chemist Martinus Van Marum was conducting experiments involving electrical sparking above water when he noticed an unusual smell, which he attributed to the electrical reactions, failing to realize that he had in fact created ozone.
Ozone (or trioxygen) is an inorganic molecule with the chemical formula O3. Ozone is a colorless gas that has an odor similar to the smell of the air after a major thunderstorm. Ozone is an unstable molecule which readily gives up one atom of oxygen providing a powerful oxidizing agent which is toxic to most waterborne organisms.