Pulverized rice husks are co-fired with natural gas in a 100 kW (rated) down-fired oxy-fuel combustor under two conditions: (1) air combustion (denoted as air) and (2) oxy-combustion with 70% O-2 and 30% CO2 in the inlet oxidant gas (denoted as OXY70). Studied in this paper are (1) mechanisms governing the partitioning of inorganic matter within the fly ash aerosol and (2) how these affect mechanisms of deposition on heat transfer surfaces. In each case, the ash aerosol particle size distributions (PSDs) were determined using electric mobility/light scattering instruments (scanning mobility particle sizer/aerodynamic particle sizer) and a Berner low-pressure impactor, where the latter collected size-segregated aerosol for subsequent analysis. The ash deposition rate was measured experimentally using a specially designed probe, and its relationship with aerosols was explored. The properties of the deposits were also investigated using a laser diffraction particle size analyzer for PSDs and scanning electron microscopy with energy-dispersive X-ray spectroscopy and X-ray diffraction for compositions. The data show that, in comparison to air, OXY70 produces greater amounts of sub-micrometer aerosols as a result of increased mineral vaporization at the higher flame temperature. Cl and P are combined with K to form KCl and KPO3 in the sub-micrometer but not in the super-micrometer aerosols. For both conditions, the particle sizes within the more loosely bound outside deposits are much larger than those within the tightly bound inside deposits. Except for S and Cl, the deposit compositions do not differ much between air and OXY70. Inside deposition rates show a positive correlation with the concentration of sub-micrometer particles, which is consistent with previous findings on coal combustion.