In 1930s, Sydney Chapman resolved the chemistry process of ozone continually regenerated by converting ultraviolet radiation (UV) into heat in the Earth’s stratosphere is known as Chapman Cycle. It describes the four steps by which O2 is photolyzed to produce O atoms and O3, which can then be photolyzed to recover O2.

Chapman Cycle for Ozone Production:

Figure 1: Ozone formation

 Ozone formation:

2 atomic oxygen is formed by the dissociation of O2 by high energy ultraviolet photons

O2 + ℎν → 2O

Each oxygen atom then quickly combines with an oxygen molecule to form an ozone molecule

O + O2 → O3

The ozone-oxygen cycle:

Ozone strongly absorbs appropriate wavelength of UV radiation and is dissociated by these UV photons into O and O2

O3 + ℎν(240-310 nm) → O2 + O

The atomic oxygen produced quickly reacts with another oxygen molecule to reform ozone

O + O2 → O3 + excess kinetic energy

Ozone Loss:

The ozone is in stable balanced by the reaction of ozone and free oxygen atoms

O3 + O· → 2 O2

 

Resources:

NASA. (June 2000)’Studying Earth’s Environment From Space’ Retrieved on 6 March, 2015 from  http://www.ccpo.odu.edu/SEES/index.html.

Unknown (2010) ‘ Ozone Layer’ Retrieved on 11 March, 2015 from  https://www.ec.gc.ca/ozone/default.asp?lang=En&n=DB5CBDE6-1

Unknown (n.d.) ‘Ozone-oxygen cycle’ Retrieved on 6 March, 2015 from http://en.wikipedia.org/wiki/Ozone-oxygen_cycle