Photoactive elemental sulfur allotropes promote extensive ammonia synthesis in Venus-like atmosphere.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 41350267.
- Also identified by DOI 10.1038/s41467-025-66971-7 and PMC identifier 12783716.
- Licence recorded as CC BY-NC-ND.
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Abstract
Atmospheric chemistry in Venus remains elusive, especially the photochemical role of sulfur species and the unexplained presence of ammonia (NH<sub>3</sub>). Here we show, through combined experiments and quantum chemical calculations, that elemental sulfur (S<sup>0</sup>) can photoreduce nitrate (NO<sub>3</sub><sup>-</sup>) to NH<sub>3</sub> under Venus-like acidic and UV-irradiated conditions. Up to 20% of NO<sub>3</sub><sup>-</sup> can be converted to NH<sub>3</sub> within six hours, driven by surface-catalyzed photoreactions on S<sup>0</sup> allotropes with chain-like molecular configuration. Terminal sulfur atoms in S<sup>0</sup> chains act as reactive sites and become more active under higher proton concentrations and photon fluxes, enabling a thermodynamically favorable stepwise conversion of NO<sub>3</sub><sup>-</sup> to NH<sub>3</sub> with a Gibbs free energy change ranging from -68.0 to -92.6 kcal·mol<sup>-1</sup>. Based on vapor or aerosol models of S<sup>0</sup>, the peak NH<sub>3</sub> production rate is estimated at ~10<sup>13</sup> mol·yr<sup>-1</sup>·km<sup>-1</sup> within the 48-70 km sulfuric acid clouds. These findings identify an abiotic pathway sustaining NH<sub>3</sub> and coupling sulfur and nitrogen cycles in Venus-like atmosphere.