What is a dangerous substance that depletes the ozone layer when released to the atmosphere?

Answer 1

Chlorofluorocarbons also called Freons

These chemicals were developed by General Motors in the late 1920s as "safe nontoxic" refrigerants to use in home refrigerators instead of the highly dangerous and toxic refrigerants then in use.

By the 1960s these chemicals were in use nearly everywhere, including as the propellant in all aerosol cans (e.g. hairspray, paint, deodorant).

By the late 1970s however it had been demonstrated that the chlorine in these chemicals could rapidly destroy the ozone in the ozone layer that blocks much of the UV light before it reaches the surface of earth, and it was decided to phase them out and find different chemicals for these uses.

These chemicals can now no longer be purchased, except when they have been recycled and are intended for use in old systems that cannot operate with the newer chemicals. Eventually these old systems will be replaced with new ones and the demand for recycled chlorofluorocarbons will cease and the loss of ozone in the ozone layer will stop and it will recover. But this will require decades.

Answer 2

Along with CFCs and HCFCs ocean brine droplets ante aerosolized by storms and blown into the atmosphere. The chlorine and bromine ions present in that solution can also impact the ozone.