Environmental Concerns of Organohalogen Use

What are CFCs and why were they once widely used?

CFCs (chlorofluorocarbons) are haloalkanes containing only carbon, chlorine, and fluorine atoms. They were widely used as refrigerant gases(refrigerators), aerosol propellants, and in air conditioning units because they are chemically very stable, non-toxic, and non-flammable — ideal properties for these applications.

How do CFCs damage the ozone layer, and what is the role of UV radiation?

When CFC molecules drift up into the upper atmosphere (stratosphere), they are exposed to high-energy UV radiation. This causes homolytic fission of the C–Cl bond, producing a chlorine radical:

CF₂Cl₂ → CF₂Cl• + Cl•

The chlorine radical then reacts with ozone (O₃) in a two-step propagation cycle:

Step 1: Cl• + O₃ → ClO• + O₂

Step 2: ClO• + O₃ → Cl• + 2O₂

The chlorine radical is regenerated in step 2, meaning it acts as a catalyst — one Cl• radical can destroy thousands of ozone molecules before eventually being removed from the cycle. This catalytic destruction depletes the ozone layer.

Why is the depletion of the ozone layer harmful, and what has been done about CFCs?

The ozone layer in the stratosphere absorbs harmful UV-B and UV-C radiation from the sun. Without it, more UV radiation reaches the Earth's surface, increasing the risk of skin cancer, cataracts, and immune system damage in humans, as well as harming ecosystems.

The Montreal Protocol (1987) led to an international agreement to phase out the production and use of CFCs, replacing them with less damaging alternatives such as HFCs (hydrofluorocarbons), which do not contain chlorine and therefore cannot produce the ozone-destroying chlorine radicals.

How do Nitrogen Dioxide (NO) damage the ozone layer too

Nitrogen oxide radicals are formed naturally during lightning strikes and also as a result of aircraft travel in the air