Question

ozone - depleting chemicals
the ozone layer is a crucial part of the stratosphere. it shields earth from harmful ultraviolet radiation. certain chemicals released at the earths surface can migrate up into the atmosphere, posing a threat to the ozone layer. scientists have noted increased ultraviolet radiation, revealing ozone holes. research identified ozone - depleting chemicals like cfcs, hcfcs, and halons. these compounds often contain chlorine.
where do chemicals released at the earths surface that threaten the ozone layer go?
migrate up into the atmosphere
solidify in the air and fall down to earth
stay close to the surface

Explanation:

The text clearly states that chemicals released at the Earth's surface that threaten the ozone - layer can migrate up into the atmosphere.

Answer:

migrate up into the atmosphere