An investigation into Venusian atmospheric chemistry based on an open-access photochemistry-transport model at 0-112 km

Atmospheric chemistry plays a crucial role in the evolution of climate habitability on Venus. It has been widely explored by chemistry-transport models, but some characteristics are still poorly interpreted. This study is devoted to developing an open-access chemistry-transport model spanning both the middle and lower atmospheres of Venus. It provides a scheme for the structure of the chemistry, especially for the sulfur and oxygen, and investigates the influence of the cloud diffusivity and the SO₂ dissolution that are adopted in the clouds. The developed model is based on the VULCAN framework and was updated with the state-of-the-art Venusian atmospheric chemistry. It includes vertical eddy diffusion retrieved recently with the Venus Express observations, and it resolves radiative transfer containing gas absorption and scattering, Mie scattering of the cloud droplets, and absorption of the unknown UV absorber. The obtained abundance profiles of SO, SO₂, CO, COS, O, O₂, O₃, HCl, and NO are in overall agreement with the observations. The results show that the increase in cloud diffusivity has slight effects on the chemical structure. The SO₂ mainly dissolves in 50–90 km and evaporates below the clouds. The rapid dissolution-release cycle is responsible for the large upward flux of SO₂ at 58 km. At around 70 km, SO has a significant peak that is larger than that of previous studies by an order of magnitude, and S and SO₂ also show slight increases. They are attributed to the buffering effects of liquid SO₂ in the clouds. O₂ is significantly eliminated by SO in this layer. We emphasize the superior regulation of the sulfur cycle on O₂ at 70 km and its potential contributions to the long-standing problem of the overestimated O₂ abundance.