The natural environment in the open air, countryside away from cities and buildings.
The environment outside of enclosed structures.
Not inside a house or under covered structure; unprotected; in the open air.
Fresh air, especially that breathed at the seaside and smelling of seaweed.
An allotrope of oxygen (symbol O₃) having three atoms in the molecule instead of the usual two; it is a toxic gas, generated from oxygen by electrical discharge.
Hypernym: greenhouse gas
To treat with ozone.