An aerosol generating device generates an aerosol having a desired particle size by passing a liquid through a flow passage heated to convert the liquid into a vapor. The flow passage includes an outlet section that controls the exit velocity of the vapor and produces an aerosol with a desired particle size. The aerosol generator can be incorporated in a hand held inhaler, and the liquid can include a medicament, which is delivered to a targeted portion of the lung using the inhaler.