光解(Photolysis)是指化合物被光分解的化学反应。

大气中最常见的光解作用有两种，

第一种是：

O₃ + hν → O₂ + OD λ < 320 nm

臭氧被光分解成了氧分子和一个处于激发态的氧原子 OD。这一氧原子会和空气中的水分子作用而生成氢氧根：

OD + H₂O → 2OH

这些氢氧根会氧化碳氢化合物，因而有如同清洁剂的效果。

第二种是：

NO₂ + hν → NO + O

这是对流层中的臭氧形成的主要化学作用。

Photodissociation, photolysis, or photodecomposition is a chemical reaction in which a chemical compound is broken down by photons. It is defined as the interaction of one or more photons with one target molecule. Photodissociation is not limited to visible light. Any photon with sufficient energy can affect the chemical bonds of a chemical compound. Since a photon's energy is inversely proportional to its wavelength, electromagnetic waves with the energy of visible light or higher, such as ultraviolet light, x-rays and gamma rays are usually involved in such reactions.