RAS question
Which gas is responsible for the depletion of the ozone layer?
Correct answer: (C) Chlorofluorocarbons (CFCs).
Chlorofluorocarbons (CFCs) are the main ozone-depleting substances responsible for depletion of the ozone layer.
Explanation
CFCs are the answer because they are the leading example of ozone-depleting substances linked to ozone loss. The UNEP Ozone Secretariat states that manmade chemicals containing halogens were identified as the main cause of ozone loss, and that the most important ozone-depleting substances were chlorofluorocarbons. The mechanism explains their impact: when a CFC molecule reaches the stratosphere, ultraviolet radiation breaks it down and releases chlorine atoms. These chlorine atoms then destroy ozone molecules catalytically, so one chlorine atom can damage thousands of ozone molecules before leaving the cycle. That is why CFCs, not the greenhouse gases listed in the other options, are the relevant cause of ozone-layer depletion here.
Why the other options are wrong
- (A) Nitrous oxide is not the best answer because the UNEP Ozone Secretariat identifies CFCs as the primary ozone-depleting substances, while nitrous oxide has only a limited ozone impact in comparison.
- (B) Carbon dioxide is a greenhouse gas, but it does not involve chlorine release or catalytic destruction of stratospheric ozone.
- (D) Methane is a greenhouse gas with minimal ozone impact here, whereas the ozone-depletion mechanism depends on CFCs releasing chlorine atoms in the stratosphere.
Concept
This tests ozone depletion under Environment and Ecology, especially the difference between greenhouse gases and ozone-depleting substances. It recurs in RAS because pollutant questions often ask for the specific environmental mechanism, not just the name of a gas.