10.11 Atmospheric Chemistry and the Ozone Layer

What is the main function of the ozone layer?

To absorb harmful ultraviolet (UV) radiation from the Sun.

What happens when ozone absorbs UV light?

It splits into O₂ and an oxygen radical (O•)

What happens to the oxygen radical (O•) produced from ozone?

It recombines with O₂ to form ozone again

What is the overall chemical change in the ozone cycle?

There is no net change — ozone is constantly destroyed and re-formed.

What is the overall energy effect of the ozone cycle?

Harmful UV light is absorbed and converted into heat energy.

Why is this energy conversion important?

It prevents UV radiation from reaching Earth’s surface and damaging living organisms.

Why could life not have developed on land without the ozone layer?

UV radiation would have destroyed DNA and cells, restricting life to the oceans.

What happens to light energy when ozone absorbs UV radiation?

It’s converted into heat, a more disordered form of energy.

Why is this conversion thermodynamically favorable?

It increases entropy by turning ordered energy into disordered energy.

What has been observed about ozone levels over Antarctica since 1975?

They have dropped to about one-third of their previous value.

What are the main health effects of increased UV exposure?

Higher rates of skin cancer, cataracts, and damage to ecosystems.

What are CFCs?

Chlorofluorocarbons — compounds containing only carbon, chlorine, and fluorine.

What were CFCs used for?

Refrigerants, aerosol propellants, foam insulation, and fire extinguishers.

Why were CFCs once considered ideal chemicals?

They were nonflammable, non-toxic, and chemically stable.

What trade name were CFCs sold under?

Freon.

Why are CFCs harmful to the ozone layer?

They rise into the stratosphere, where UV light breaks them apart to form chlorine radicals that destroy ozone.

What does the depletion of the ozone layer cause on Earth?

More UV radiation reaching the surface, leading to health and environmental damage.

What does HFA stand for?

Hydrofluoroalkane.

How do HFAs differ chemically from CFCs?

HFAs have C–F and C–H bonds but no C–Cl bonds

Why are HFAs less damaging to the ozone layer?

The C–F bond is much stronger and not easily broken by UV light, so no chlorine radicals are released.

Why was switching from CFCs to HFAs difficult?

HFAs have different properties that required redesigning refrigeration systems and retesting medical inhalers.

What environmental issue is associated with HFAs?

They are powerful greenhouse gases that contribute to climate change

How potent are HFAs compared to CO₂ as greenhouse gases?

One mole of an HFA can be thousands of times more potent than one mole of CO₂

Why are HFA-based inhalers more expensive than older CFC inhalers?

The new propellants and testing requirements increase production costs.

Are HFAs a perfect solution?

No; they protect ozone but worsen the greenhouse effect, so research continues for safer, cheaper alternatives.