What is the purpose of ozone in the atmosphere?

Ozone in the atmosphere primarily serves the crucial function of protecting Earth from harmful ultraviolet (UV) rays emitted by the sun. The ozone layer, situated in the stratosphere, absorbs the majority of the sun's damaging UV radiation, thus preventing it from reaching the Earth's surface where it can cause skin cancer, cataracts, and other serious health issues in living organisms. Additionally, it plays a vital role in maintaining the balance of the ecosystem by protecting the biodiversity of various species, especially those sensitive to UV exposure.

While the other options refer to processes related to atmospheric and environmental changes, they do not capture the fundamental role that ozone plays in shielding the planet from UV radiation. Enhancing the greenhouse effect and increasing air temperature are related to other gases, primarily carbon dioxide and methane, while promoting photosynthesis is a function associated with light availability and carbon dioxide, rather than ozone itself. Thus, the correct choice highlights ozone's protective role, crucial for the health of organisms and ecosystems on Earth.