Altitude (a) and pressure (b) profiles of the Ar⁺model-to-observation density ratio under different input conditions. Results with H₂ excluded (magenta lines), a lower rate coefficient for the Ar⁺+CO₂ reaction (dashed green lines), a 50% reduction in solar irradiance (gray lines), and a combination of the lower rate coefficient, reduced solar irradiance (dashed gray lines), and a reduction of CO densities by an order of 6.5 are shown in each panel.