Certified in Public Health (CPH) Practice Exam

Which of the following pollutants is known to contribute to the deterioration of the stratospheric ozone layer?

1. Carbon dioxide

2. Chlorofluorocarbons (CFCs)

3. Methane

4. Nitrogen oxides

The correct answer is: Chlorofluorocarbons (CFCs)

Chlorofluorocarbons (CFCs) are known for their significant role in the depletion of the stratospheric ozone layer. CFCs, man-made chemical compounds that were widely used in refrigeration, air conditioning, and aerosol propellants, release chlorine atoms when they break down in the stratosphere. These chlorine atoms react with ozone (O3) molecules, leading to the destruction of the ozone layer that protects the Earth from harmful ultraviolet (UV) radiation. This mechanism of ozone depletion has been a critical environmental issue, leading to international agreements like the Montreal Protocol to phase out the production and consumption of CFCs. In contrast, carbon dioxide mainly contributes to greenhouse gas effects and is not directly linked to ozone layer deterioration. Methane also acts as a greenhouse gas and, while it has some indirect effects on ozone at ground level, it does not interact with stratospheric ozone in the same destructive way as CFCs. Nitrogen oxides can lead to ozone depletion, but their impact is significantly overshadowed by the effects of CFCs, which are the principal agents of ozone layer destruction. Hence, the distinct characteristic of CFCs in this context makes them the correct answer regarding pollutants contributing to