1D model studies of Venusian sulfur cycles in the clouds and atmospheric chemistry

Venus has recently garnered significant attention with the approval of three new missions: EnVision (ESA), DAVINCI+ (NASA), and VERITAS (NASA). Among the most important features of Venus, its thick clouds play a crucial role in regulating the current environment, influencing mission planning, and affecting planetary evolution and habitability. The sulfuric acid clouds are governed by the sulfur cycle, which exhibits considerable spatial and temporal variations and remains largely unknown. Furthermore, most chemical models treat the clouds as fixed boundaries to simulate the atmosphere above or below them, thereby avoiding the complexities of cloud calculations. Consequently, the sulfur-bearing species above and below the clouds are often inconsistent across these studies, particularly regarding SO₂ and SO₃.

Given that sulfur originates from chemical processes and that clouds feedback into the chemistry through dynamics, radiative transfer, and gas-liquid exchange, we emphasize the critical coupling effect between clouds and atmospheric chemistry in regulating the sulfur cycle on Venus. In light of this, we have undertaken a series of efforts.

Firstly, we developed a 1D H₂SO₄-H₂O binary condensation model to trace cloud cycles and investigate the impact of cloud acidity on the condensation process. This model generates self-consistent profiles of gas and liquid abundances of relevant species, cloud mass loading, acidity, and particle size that align with observational data. We found that the significant supersaturation of H₂SO₄ in the upper clouds is regulated by its chemical production rate. Based on this finding, we further simplified the condensation processes and constructed a semi-analytical cloud model, which significantly reduces the computational time for Venusian cloud modeling to just 15 seconds per run, facilitating cloud coupling studies.

Additionally, we developed a 1D atmospheric chemistry-transport model for Venus that spans the middle and lower atmospheres, incorporating updated chemical processes. The derived abundances of crucial species are consistent with observations. Our results confirm that the rapid dissolution-release cycle of SO₂ could lead to its significant gradient within the clouds. This study suggests that liquid SO₂ in the clouds may buffer variations in sulfur-bearing species and that the sulfur cycle could influence O₂ abundance. Our next step is to couple the cloud model and the photochemical model to explore the feedback of clouds on the atmosphere in greater detail.