Hierarchy classification:

1. top of the aat hierarchies
2. Materials Facet
3. Materials (hierarchy name)
4. materials (substances)
5. [materials by composition]
6. inorganic material
7. [oxygen, oxygen isotopes, allotropes, compounds]
8. oxygen allotropes

Anotations

Scope note:

An allotropic form of oxygen, O3, which is a bluish toxic gas with a characteristic sharp odor, is a powerful oxidizing agent, and is produced from molecular oxygen by electrical discharge and in the upper atmosphere by ultraviolet light.