The phenomenon of aerosol formation is often watched in industrial wet scrubbing processes especially if strong acid gases are absorbed in aqueous solutions. Although the basic principles of aerosol formation are well known in general, there exist nearly no specific rules for the design of industrial processes in which aerosol formation can be expected. There are two reasons for the fragmentary knowledge concerning aerosol formation in wet scrubbing processes. Firstly, it is a very complex task to describe the formation and the growth of aerosols theoretically under typical conditions of industrial processes. Secondly, no reliable experimental data, especially for the validation of theoretical work, has been available to date. To bridge this gap, a semi-technical wet scrubbing plant has been developed and erected in which the formation and the growth of aerosols under realistic conditions can be studied and the characteristic aerosol parameters can be measured in situ. It is shown that HCl-aerosols are formed in a quench cooler for hot flue gases of about 200 degrees C even at low HCl feed concentrations of about 1000 mg m(-3), but only in the presence of foreign nuclei. The aerosol droplets in the quench cooler grow up to 1-1.5 mu m and can be enlarged in a direct-contact-cooling column up to about 2.5 mu m. Furthermore, a strategy for aerosol evaporation is discussed.