Some of the longer wavelength radiation is able to ionise nitrous oxide in the D-region, and the short wavelength X rays will ionise all gases present. Cosmic rays also produce ionisation which is of relative importance below 70km. The figure below shows these, along with the combined production rates. If there were no processes by which ionisation was lost the atmosphere would become fully ionised. Since this is not the case there must be an equilibrium reached between the production and loss of ionisation.
Radiative recombination is a very slow process and can be virtually ignored.
Dissociative recombination can only take place where there are either molecular ions produced directly or where molecular ions can be produced by ion-atom exchange, which requires neutral molecules. In the E region the peak of production is at around 110-115 km. Plenty of molecular gas is present at this height so molecular ions are produced directly and the loss rate is controlled by dissociative recombination. The F region In the F region the peak of production is at around 150-160km. Through the F region the loss rate gradually becomes controlled by the ion-atom exchange rate and this rate decreases with increasing height.