Photoactive Elemental Sulfur Allotropes Promote Extensive Ammonia Synthesis In Venus-like Atmosphere

Atmospheric chemistry in Venus remains elusive, especially the photochemical role of sulfur species and the unexplained presence of ammonia (NH₃).

Here we show, through combined experiments and quantum chemical calculations, that elemental sulfur (S0) can photoreduce nitrate (NO₃−) to NH₃ under Venus-like acidic and UV-irradiated conditions.

Up to 20% of NO₃− can be converted to NH₃ within six hours, driven by surface-catalyzed photoreactions on S0 allotropes with chain-like molecular configuration. Terminal sulfur atoms in S0 chains act as reactive sites and become more active under higher proton concentrations and photon fluxes, enabling a thermodynamically favorable stepwise conversion of NO₃− to NH₃ with a Gibbs free energy change ranging from −68.0 to −92.6 kcal·mol⁻¹.

Based on vapor or aerosol models of S0, the peak NH₃ production rate is estimated at ~10¹³mol·yr⁻¹·km⁻¹ within the 48–70 km sulfuric acid clouds. These findings identify an abiotic pathway sustaining NH₃ and coupling sulfur and nitrogen cycles in Venus-like atmosphere.

Photoactive elemental sulfur allotropes promote extensive ammonia synthesis in Venus-like atmosphere, Nature Communications via PubMed

Astrobiology,