An aerosol generator useful as an atomizer for controllably and reproduci producing wet or dry aerosols for inhalation studies, including a nebulizer for producing an aerosol from a liquid and an air stream, a liquid dosing device such as a step dosing pump for controllably feeding a liquid to be atomized to the neubilizer, an apparatus such as a mass flow controller for regulating the flow of an air stream to the nebulizer to provide an amount needed to atomize the liquid, and optionally to dilute the resulting aerosol, a conduit for conveying the aerosol formed in the nebulizer to an aerosol exposure chamber, a measuring device such as a light-scattering diffusion photometer into which a sample of the aerosol is introduced for determining the concentration of the aerosol, and a control unit for controlling the liquid supply device and the adjustable air supply to produce an aerosol having a predetermined desired concentration; the control unit being operated either manually or by a computer responsive to measured values determined by the measuring device.