What is a major cause of ozone layer depletion?

Chlorofluorocarbons (CFCs) are one of the primary substances responsible for ozone layer depletion. CFCs are synthetic compounds that were widely used in refrigeration, air conditioning, and aerosol propellants. When released into the atmosphere, CFCs eventually reach the stratosphere, where they undergo photodissociation due to ultraviolet (UV) radiation. This process releases chlorine atoms, which can then catalytically destroy ozone molecules.

Ozone in the stratosphere serves a crucial role in blocking UV radiation from the sun, protecting life on Earth. The depletion of this layer allows more harmful UV radiation to reach the Earth's surface, which can lead to increased rates of skin cancer, cataracts, and other environmental issues.

While carbon monoxide and hydrocarbons do have environmental impacts, such as contributing to air pollution and smog, they do not play a significant role in the depletion of the ozone layer. Therefore, CFCs are recognized as the major cause of ozone layer depletion, making them the correct answer in this context.