What they are: Aerosols are the chemicals used as propellants in spray cans — deodorants, perfumes, paints and insecticides. Many of them contain CFCs (chlorofluorocarbons).
Their harmful effects:
1. They destroy the ozone layer.
On reaching the upper atmosphere, UV rays break the CFC molecules and release free chlorine atoms:
$$Cl + O_3 \rightarrow ClO + O_2$$
A single chlorine atom can destroy thousands of ozone molecules, because it is released again each time.
2. More UV radiation reaches the earth.
With the ozone layer thinned, the harmful ultraviolet rays come through and cause skin cancer, cataract and damage to the immune system.
3. They harm crops and marine life.
UV radiation damages crops and kills the plankton on which the whole marine food chain depends.
4. They add to global warming.
CFCs are also greenhouse gases, and far more powerful than carbon dioxide.
5. Health problems.
Breathing in aerosol sprays can cause irritation of the eyes, throat and lungs.
Step taken: The Montreal Protocol (1987) got countries to cut CFC production, and today most sprays are marked "CFC-free".
