Which of the following is NOT a factor in the formation of ozone?

Ozone is formed in the atmosphere primarily through a photochemical process involving ultraviolet (UV) light, oxygen molecules, and various reactive chemicals. The process generally occurs when UV light acts on oxygen molecules (O2), leading to the formation of ozone (O3).

While UV light and oxygen molecules are directly involved in the formation of ozone, chlorine plays a role in atmospheric chemistry that can lead to ozone depletion rather than formation. Chlorine is a reactive element that can break down ozone molecules in the stratosphere, notably through chlorofluorocarbons (CFCs) and other compounds.

Carbon monoxide, on the other hand, does not contribute to the production of ozone. While it can indirectly affect ozone levels by influencing the atmosphere's reactivity and the behavior of other pollutants, it is not a primary ingredient or factor in ozone formation. Therefore, it is appropriate to identify carbon monoxide as the substance that does not belong in the context of ozone formation.