Stable nanosuspensions could be obtained by separation of gasborne organic nanoparticles in bubble columns with surfactant-containing solutions. At high concentrations as they are encountered in the RESSAS process (rapid expansion of supercritical solution into aqueous solution), the transfer of nanoparticles from the gas phase into the liquid is superimposed by agglomeration in the gas phase. A model to account for both processes and an approach for its application to the complex flow field in a RESSAS apparatus for the synthesis of stable naproxen nanosuspensions are presented.