= Dependence of a quench diffusivity on mixing length
{title2=$K_{zz}\gtrsim\ell^2/\tau_{\rm chem}$}
For a vertical <eddy diffusivity> $K_{zz}$, mixing over a length $\ell$ takes $\tau_{\rm mix}\sim\ell^2/K_{zz}$. The condition that transport outrun a <chemical relaxation time> therefore gives $K_{zz}\gtrsim\ell^2/\tau_{\rm chem}$. Taking $\ell=0.1H$ instead of one <atmospheric scale height> $H$ changes this estimate by a factor of one hundred. The <atmospheric scale height> itself depends on both temperature and gravity.
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