Formaldehyde (Methanal) is the chemical compound with the formula H2CO. The simplest aldehyde, it was first synthesized by the Russian chemist Aleksandr Butlerov but was conclusively identified by August Wilhelm von Hofmann. Formaldehyde exists in several forms aside from H2CO: the cyclic trimer (troxane) and the polymer (paraformaldehyde). Additionally, in water, it exists as the hydrate H2C(OH)2.
Formaldehyde is an intermediate in the oxidation (or combustion) of methane as well as other carbon compounds. It can be found in the smoke from forest fires, in automobile exhaust, and in tobacco smoke. In the atmosphere, formaldehyde is produced by the action of sunlight and oxygen on atmospheric methane and other hydrocarbons. It thus becomes part of smog pollution. Small amounts of formaldehyde are produced as a metabolic byproduct in most organisms, including humans.