Carbon monoxide–methane quenching ($\mathrm{CO}\rightleftharpoons {\mathrm{CH}}_4$ quenching)

Carbon monoxide–methane quenching preserves a transported carbon partition after local reactions become too slow to restore thermochemical equilibrium. A useful net reaction isThis is a net stoichiometric balance, rather than a single elementary reaction whose rate can simply be read from the equation. Temperature, pressure and the kinetic pathway determine the preferred composition and conversion time.

In models of hot Jupiters, vertical transport can maintain methane away from its local equilibrium abundance, while atmospheric photochemistry removes it at higher levels.^[ref] A methane band therefore probes both chemistry and circulation, rather than acting as a unique local temperature measurement.