= Solution
Three solar-system effects illustrate <chemical disequilibrium>. First, vertical mixing carries <carbon monoxide> from hot deep regions into cooler observable layers of giant planets, where its local-equilibrium abundance would be small. Second, <phosphine> survives in the observable atmospheres of Jupiter and Saturn because deep supply competes with its destruction, making it a tracer of transport. Third, <methane> photolysis creates hydrocarbons such as ethane and <acetylene>, and can help form upper-atmospheric <atmospheric hazes> in giant planets and Titan.
Three exoplanet effects are complementary. First, <carbon monoxide–methane quenching> can keep <carbon monoxide> abundant and <methane> depleted in cool observable gas, including hot-Neptune/giant atmospheres that would locally favor <methane>. Second, <atmospheric photochemistry> dissociates <methane>/<ammonia> and produces radicals, <hydrogen cyanide>, hydrocarbons and possibly <atmospheric hazes>, changing spectral bands from their equilibrium strengths. Third, <horizontal chemical quenching> can preserve hot-dayside carbon chemistry on the cooler nightside/terminator and reduce the abundance contrast expected from separate local-equilibrium columns.
\b[Transport, photon-driven reactions and finite chemical adjustment times change the observable composition]. The effects are conditional on the species' chemical timescale relative to mixing, advection and irradiation; they do not imply that every molecule is out of equilibrium everywhere.
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