Odd oxygen ($O_x=\mathrm{O}+{\mathrm{O}}_3$)

A chemical-family bookkeeping variable in a simple stratospheric model. Interconversion of atomic oxygen and ozone preserves this count, while $\mathrm{O}+{\mathrm{O}}_3\to 2{\mathrm{O}}_2$ removes two units. The definition must be extended consistently when including additional reservoirs or excited atomic states.

A basic oxygen–ozone mechanism combining oxygen photodissociation, three-body ozone formation, ozone photodissociation and $\mathrm{O}+{\mathrm{O}}_3\to 2{\mathrm{O}}_2$. The last reaction removes two units of odd oxygen; a catalytic cycle can add another loss pathway.

Suppose a reduced steady balance is $P=A{X}^2+BX$, where $X=[{\mathrm{O}}_3]$, and hold $P$ and all specified background concentrations fixed. With $u=1/T$, $d\ln A/du=-a$ and $d\ln B/du=-b$, implicit differentiation gives $d\ln X/du=(aA{X}^2+bBX)/(2A{X}^2+BX)$. The quadratic loss term includes temperature-dependent O/O3 partitioning as well as the direct reaction coefficient. Holding the loss ratio fixed over a finite change is an additional approximation; solving the new quadratic provides a check.