In the PGSS process, a gas saturated solution is atomized through a nozzle and a spray is formed; afterwards, the gas (carbon dioxide) evaporates and droplets solidify. In this work, the behaviour of a carbon dioxide super-saturated solution drop in a low pressure environment is investigated. A mathematical model, based on the general multi-component equations of change and on the Stefan conditions to account for the moving boundaries, is solved numerically providing the spatial and temporal profiles of temperature, composition, mass flow inside and outside the droplet. The time required to attain the solid-liquid equilibrium condition at the droplet boundary decreases monotonically when the initial carbon dioxide content is increased, and increases together with the initial solution temperature. These trends are consistent with experimental data, showing that the average final particle size decreases if the mixing vessel pressure is raised and increases together with the spray temperature. (c) 2006 Elsevier B.V. All rights reserved.