Comparison of various time constants. Left: comparison of the ion diffusion time constant (τ_diff) and ion chemical destruction time constant (τ_chem) for several selected species, where τ_diff includes the contributions from both ion-neutral collisions and ion-ion Coulomb collisions. Right: comparison of the ion-neutral collision time constant (τ_in) and ion-ion Coulomb collision time constant (τ_ii) for the same species. All time constants are based on our solar minimum calculations appropriate for the dayside averaged condition.