Primary (photon impact) and secondary (photoelectron impact) processes driving dayside Martian upper atmospheric chemistry in the nominal model simulation. (a) Altitude variation in the incident solar SXR and EUV spectrum. The thick solid line indicates the wavelength-dependent penetration depth, defined as the altitude at which the solar irradiance drops to 1/e of its value at the top of the atmosphere. (b) Altitude variation in the sum of the upward and downward hemispheric photoelectron fluxes derived from the two-stream model. This quantity is directly proportional to the total, omnidirectional photoelectron intensity, which is the critical input for computing secondary ionization rates. (c) Photoionization and photodissociation rate profiles of CO₂ for selected channels. (d) Production rate profiles for selected ion species, with solid and dashed lines denoting primary and secondary production, respectively.