Hydroxyl radical is a chemical species that is highly reactive and plays an important role in various biochemical and atmospheric reactions. It is also known as the hydroxy radical and the OH radical. The hydroxyl radical is formed in the atmosphere due to the photochemical reaction of ozone and water vapor. It is also produced by biological systems during various metabolic processes. Some other synonyms for hydroxyl radical include hydroxy ion, superoxide radical, hydrogen peroxide radical, and perhydroxyl radical. These different chemical species have their own unique properties and effects on their surrounding environment. Studying the properties and interactions of these species is important in understanding the fundamental chemical processes that take place in biological and environmental systems.