"Lower down, the atmospheric temperature reaches a maximum of ∼110 K around 30 km altitude (Hinson et al., 2017). Some evolution as haze particles settle through this warm zone seems inevitable. The  temperature is high enough to cause sublimation of more volatile hydrocarbons and nitriles that condensed onto the haze particles higher  up in the atmosphere, but only if they condensed rather than being more strongly adsorbed or even chemically bonded into the macro molecular tholin (e.g., Luspay-Kuti et al., 2017).  Sublimation loss would 

shrink the haze particles and slow their settling, as well as modifying their compositions by distilling off the more volatile constituents. 110 K  also exceeds the zero pressure melting points of some of the constituent hydrocarbon species, specifically C2H4 (104 K), C2H6 (90 K), and C3H6  (88 K). Unmelted species may partly dissolve into those that do melt,  and melting point depression can be expected in such mixtures (for instance, the CH4eC2H6 eutectic melting point is 18 K below the melting points of the pure species; Hanley et al. (2017)). Partial melting  could allow particles to evolve from fractal aggregate shapes into more  compacted spherical forms, due to surface tension, with implications  for their scattering properties and settling rates. Warmed haze particles  might also be more sticky and could coalesce into even larger aggregates if they contact one another."