We present a Monte Carlo study of galactic cosmic-ray energy deposition and its implications for stratospheric chemistry, performed with the geant4 toolkit. Primary nuclei (protons, $\alpha$, CNO, and Si) were propagated through an atmosphere modeled from 0 to $120\mathrm{g}{\mathrm{cm}}^{-2}$, considering both polar ($R_{\mathrm{c}}=0.1\mathrm{GV}$) and equatorial ($R_{\mathrm{c}}=15\mathrm{GV}$) geomagnetic cutoff conditions. The simulations resolve the variation of energy deposition with altitude for primary and secondary particles, revealing that $\sim 96\%$ of the stratospheric energy budget arises from cascade secondaries within the 15–35 km domain. By converting layer-resolved energy deposition into ion pair production rates, we quantify the resulting formation of odd-nitrogen (${\mathrm{NO}}_{\mathrm{x}}$) and odd-hydrogen (${\mathrm{HO}}_{\mathrm{x}}$) radicals, which catalyze the destruction of ozone. The modeled production rates peak between 18 and 22 km altitude, leading to an estimated fractional ozone decrease of the order of ${10}^{-3}-{10}^{-2}$ under average galactic cosmic-ray fluxes, consistent with observed background modulation over the solar cycle. These results establish a physically consistent link between cosmic-ray-induced energy deposition and ozone chemistry, providing a benchmark framework for coupling high-energy particle transport to atmospheric photochemical models.

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• Particle interactions
• Particle phenomena