What is primarily responsible for damage to rubber caused by sunlight?

The primary factor responsible for damage to rubber caused by sunlight is ozone. When rubber is exposed to ultraviolet (UV) light found in sunlight, a reaction takes place where ozone in the atmosphere interacts with the rubber material. This interaction leads to the degradation of the rubber's molecular structure, causing it to become brittle, cracked, and overall less effective. The presence of ozone accelerates the aging process of rubber, making it particularly susceptible to weathering when exposed to open air and sunlight.

Other elements like heat, moisture, and friction do have impacts on rubber, but the specific degradation from sunlight is most directly attributed to the chemical reactions involving ozone. Heat can exacerbate these processes but is not the root cause, while moisture can lead to mold or mildew, and friction contributes to wear and tear but does not directly dismantle the rubber's integrity like ozone does.