Variations in column abundances of H, O, and CO₂ at the surface, the evolution of isotope ratios of Ne and Ar, and the evolution of escape altitude, shown from top to bottom. The left panel shows the results of the escape scenarios calculated using the radiative-convective atmosphere model only at the initial time step for the escape base height, r₀ , followed by calculations based on the energy-limited escape model. The right panel shows the results of our atmospheric structure-escape coupling model, with r₀ updated at each time step. The purple and light red shaded regions represent the current Venusian atmosphere ranges of ²⁰Ne/²²Ne, ³⁶Ar/³⁸Ar, and ²⁰Ne/³⁶Ar – 11.8 ± 0.7, 5.5 ± 0.6, and 0.25 ± 0.1, respectively (von Zahn et al. 1983; Donahue & Pollack 1983). Note: the ²⁰Ne/³⁶Ar ratio is assumed to evolve from 0.33, a value that is strongly fractionated compared to the solar value 44.7. Also, z₀ = r₀ –R_Venus represents the height from the base of the escape flow to the surface of Venus.