a colorless gas (O3) soluble in alkalis and cold water; a strong oxidizing agent; can be produced by electric discharge in oxygen or by the action of ultraviolet radiation on oxygen in the stratosphere (where it acts as a screen for ultraviolet radiation), Fresh air, especially that breathed at the seaside and smelling of seaweed, chemistry An allotrope of oxygen (symbol O3) having three atoms in the molecule instead of the usual two; it is a blue gas, generated from oxygen by electrical discharge; it is poisonous and highly reactive, but in the upper atmosphere it protects life on Earth from ultraviolet radiation