Corrosion is the chemical or electrochemical reaction between a material, usually a metal, and its environment that produces a deterioration of the material and its properties. Usually corrosion is the oxidation of metals in the presence of water or water vapor, and is known as rust (iron, steel) while rust (galvanized steel), and other terms of corrosion failures such as tarnish, pitting and flaking.
There are many different types of corrosion including atmospheric corrosion, corrosion in waters, corrosion in soils, corrosion in chemical environments, mechanically assisted corrosion, high-temperature corrosion, microbiologically influenced corrosion, etc. From an economic safety and aesthetic standpoint, atmospheric corrosion is one of the most important types of corrosion. Atmospheric corrosion is enabled by atmospheric humidity and stimulated by pollutants in the atmosphere such as acid gases [sulfur dioxide (SO2), hydrogen sulfide (H2S), and carbon dioxide(CO2)], nitrogen oxides (NO and NO2), ozone (O3), and salts (chlorides and sulfides).