Editing Ozone–oxygen cycle (section)

===[[Mesosphere]]===

In the mesosphere, oxygen photodissociation dominates over ozone photodissociation, so we have approximately:<ref name="Photochemistry of Ozone" />
:(rate of reaction 2) = (rate of reaction 1) =  (rate of reaction 4)

Thus, ozone is mainly removed by ozone conversion. Both ozone creation and conversion depend linearly on oxygen atom concentration, but in ozone creation an oxygen atom must encounter an oxygen molecule and another air molecule (typically nitrogen) simultaneously, while in ozone conversion an oxygen atom must only encounter an ozone molecule. Thus, when both reactions are balanced, the ratio between ozone and molecular oxygen concentrations is approximately proportional to air density.

Therefore, the relative ozone concentration is higher at lower altitudes, where air density is higher. This trend continues to some extent lower into the stratosphere, and thus as we go from 60&nbsp;km to 30&nbsp;km altitude, both air density and ozone relative concentration increase by ~40-50-fold.<ref name="NASA">[https://ozonewatch.gsfc.nasa.gov/facts/SH.html NASA Ozone Watch]</ref><ref>Bakhmetieva, N. V., Kulikov, Y. Y., & Zhemyakov, I. N. (2020). Mesosphere ozone and the lower ionosphere under plasma disturbance by powerful high-frequency radio emission. Atmosphere, 11(11), 1154.</ref><ref>[https://www.engineeringtoolbox.com/standard-atmosphere-d_604.html#google_vignette  The Engineering Toolbox: U.S. Standard Atmosphere vs. Altitude ]</ref>