Vertical profiles of eddy diffusivity in typical 1D chemical models of planets in and out of the solar system. Sources: Zhang et al. (2012) for Venus; Allen et al. (1981) for Earth; Nair et al. (1994) for Mars; Li et al. (2015) for Titan; Wong et al. (2017) for Pluto; Moses et al. (2005) for Jupiter, Saturn, Uranus, and Neptune; Moses et al. (2013) for GJ436b; and Moses et al. (2011) for HD189733b and HD209458b. For HD209458b, we show eddy diffusivity profiles assumed in a gas chemistry model (dashed line, Moses et al. 2011) and that derived from a 3D particulate tracer-transport model (solid line, Parmentier et al. 2013).