Towards the investigation of chemical effects of energetic electrons and photons in the atmosphere

Terrestrial gamma-ray flashes (TGFs) are bursts of energetic X- and gamma-rays which are emitted from thunderstorms as the Bremsstrahlung radiation of relativistic electrons. Recently, the ALOFT (Airborne Lightning Observatory for FEGS and TGFs) mission has shown that the emission of such energetic radiation, also including gamma-ray glows and flickering gamma-ray flashes, is more abundant than previously thought. This raises the question how the relativistic electrons and photons interact with the atmosphere and whether they have an impact on the chemical composition while propagating through the atmosphere, potentially relevant for the production of greenhouse gases. The propagation and interaction of relativistic particles with the atmosphere can be studied with particle Monte Carlo collision models requiring cross sections as an input. Whilst there are well established data for photoionization, Compton scattering and pair production, we lack cross sections for photoexcitation, photodissociation or the excitation of air molecules through relativistic electrons which contribute to the chemical activation of the atmosphere. In order to fill this gap of data, we here present a novel numerical tool calculating cross sections for energetic particles propagating in air. We provide an overview of the code structure and present benchmarking cases against well-known cross sections. Additionally, we will present a first application by calculating cross sections for photodissociation for a wide range of energies. In the end, we will give an outlook how this will allow to pave the path for more realistic simulations of energetic phenomena in our atmosphere, relevant for chemical processes.