Comparison of key timescales in the nominal model: the chemical timescale τ^(c), the binary diffusion timescale τ^(d), the eddy diffusion timescale τ^(e), and collision timescales for different processes including τ⁽ⁱⁿ⁾ for ion–neutral collisions, τ⁽ⁱⁱ⁾ for ion–ion Coulomb collisions, τ⁽ⁿⁿ⁾ for neutral–neutral collisions, and τ⁽ⁿⁱ⁾ for neutral–ion collisions (representing ion drag on neutrals). (a) Chemical and binary diffusion timescales for major ions. (b) Chemical, binary diffusion, and eddy diffusion timescales for selected minor neutrals. (c) Ion–neutral and Coulomb collision timescales for major ions. (d) Neutral–neutral collision and ion drag timescales for selected minor neutrals. Note: the neutral–neutral collision timescales in panel (d) are multiplied by a factor of 10 for visual clarity.