The device for forming an aerosol has a device for adjusting the amount of particle former transported by the spray jet per time unit and/or a device for adjusting the amount of compressed gas passing per time unit through the wall. Such a device can be used for fluid treatment of sensitive, easily deformable objects, especially for their cooling, or other applications requiring certain metering of the particle formation, for example, in a burner. By providing a permeable wall having pores, it is possible to produce fluid particles with minimal kinetic energy by the effect of the compressed gas flowing through the permeable wall so that at the exit side of the wall a fluid particle stream with particles having extremely low energy per particle can be produced.