The formation of stratospheric ozone (O3) occurs primarily through a series of chemical reactions involving ultraviolet (UV) radiation and several key atmospheric gases. The primary reaction involved in ozone formation is the conversion of oxygen molecules (O2) into ozone molecules (O3) through the following reaction:
O2 + UV radiation -> 2 O
2 O + O2 -> 2 O3
The first step of the reaction, the dissociation of O2 by UV radiation, creates two highly reactive oxygen atoms (O). These oxygen atoms then quickly react with another O2 molecule, forming an ozone molecule (O3).
Another important reaction that contributes to ozone formation is the conversion of methane (CH4) and other hydrocarbons into water vapor (H2O) and carbon dioxide (CO2), which release atomic oxygen (O) as a byproduct:
CH4 + 2 O2 -> CO2 + 2 H2O + O
The atomic oxygen produced in this reaction can also react with O2 to form ozone.
Additionally, several other chemical reactions also contribute to ozone formation. For example, nitric oxide (NO) can react with atomic oxygen to form NO2 which again can react with more atomic oxygen to produce ozone. Also, chlorine, bromine and iodine compounds can catalyze the breakdown of ozone, particularly in the Antarctic stratosphere, releasing chlorine and bromine atoms that can destroy many ozone molecules.