TL;DR: Since no one is answering, I am taking take the responsibility. Yes, just like @uhoh said, there are two size modes with mean radii ~0.2 µm (mode 1) and ~1 µm
60 (mode 2), along with a third, controversial mode with radius ~3.5 µm.
The main cloud deck extends from about 48 km up to ∼70 km. It can be subdivided in three layers according to the behaviour of extinction coefficient and particle population.
- The upper cloud (57–70 km) is populated by submicron (r1∼0.2 μm) and
micron size (r2∼1 μm) particles. This is the altitude range where
the photochemical “factory” producing sulphuric acid from
SO2 and H2O is located.
- The middle and lower clouds are separated from upper clouds a 1–2 km gap with
reduced extinction located at ∼56 km. Below that level the cloud
density gradually increases with depth reaching its maximum at ∼50
km. This region is characterized by tri-modal particle distribution
with typical radii of 0.15-0.2 μm (mode 1), 1-1.25 μm (mode 2) and
3.5-4.0 μm (mode 3). Sulphuric acid was found to be the major aerosol
constituent in the middle clouds, although significant elemental
abundances of chlorine and phosphorous were also found at these altitudes.
Extended layers of fine aerosols are observed both above and below the main cloud level. The upper haze fills the mesosphere up to ∼100 km altitude with evidences of detached layers. The haze is presumably composed of very very fine particles of sulphuric acid. The lower haze extends down to ∼33 km, far below the level of sulphuric acid thermal decomposition. Descent probes also provided some evidence for thin aerosol layers near the surface.
- Titov, D.V., Ignatiev, N.I., McGouldrick, K. et al. Clouds and Hazes of Venus. Space Sci Rev 214, 126 (2018). DOI: 10.1007/s11214-018-0552-z