Comparison of various ion density profiles based on our solar minimum model calculations, including the total ion (or electron) density profile (denoted as “e”), the summed density profile of all non-protonated ions (denoted as “NP”), the summed density profile of all protonated ions (denoted as “P”), as well as the density profiles of the two most abundant protonated species (OH⁺ and HCO⁺).