The part of the atmosphere most affected by UV rays is the stratosphere, specifically the ozone layer.

Here's why:

* Ozone layer: This layer contains a high concentration of ozone gas (O3). Ozone molecules are very effective at absorbing UV radiation, particularly the harmful UVB rays.

* Absorption of UV radiation: When UV radiation hits an ozone molecule, it breaks the molecule apart. This process absorbs the UV energy, preventing it from reaching the Earth's surface.

* Protection from harmful radiation: The ozone layer acts as a shield, protecting life on Earth from the damaging effects of UV radiation, such as skin cancer, cataracts, and damage to plants and ecosystems.

While other layers of the atmosphere also interact with UV radiation to some degree, the stratosphere and its ozone layer play the most crucial role in filtering out harmful UV rays.