Photoionization is a process in which an atom or molecule absorbs a photon, typically from ultraviolet or X-ray light, leading to the ejection of one or more electrons. This results in the formation of positively charged ions. The energy of the incoming photon must be greater than the binding energy of the electron for ionization to occur. This phenomenon is significant in various fields, including astrophysics and atmospheric science. For instance, in space, photoionization helps explain the behavior of stellar winds and the formation of nebulae. In the atmosphere, it plays a role in the chemistry of ozone and other gases.