The physics and chemistry of dust in the interstellar medium have many similarities with those for terrestrial aerosols, though on a much different scale. Certain chemical reactions in interstellar conditions may only occur on the surface of a host particle and interstellar dust plays a catalytic role in enabling such reactions. The chemical kinetics for reactions in the sparse conditions of the ISM is equally applicable to that for heterogeneous chemical kinetics of trace gases in terrestrial conditions involving aerosols. In both cases, a stochastic approach to the kinetics may be needed to replace the traditional mean field approach.
A closely related problem is to calculate the size distribution of the host dust/aerosol particles. Non-carbon dust in space has a strong metal oxide component and the formation mechanism has only recently started to be understood. On the other hand, carbon dust formation around stars is thought to proceed via the production of polycyclic aromatic hydrocarbons (PAHs) from smaller gaseous species. Once a critical PAH species is formed, further growth occurs mostly through the agglomeration and surface growth of this critical species. The process is similar to that of soot formation during incomplete combustion of fossil-derived fuels on earth. Numerical modelling of this process is non-trivial, as particle sizes ranging several orders of magnitude are involved, rendering the calculations computationally intractable.
Accurate modelling of these processes is at the heart of understanding how complex molecules, including prebiotic molecules, may have formed in the nebular soup that created the Solar System.