Aerosols of industrial significance like ammonium chloride, hydrochlor
ic acid and sulphuric acid aerosols have been generated with particle
number concentrations between 10(6) and 10(8) cm(-3) and particle size
s between 0.1 and 0.5 mu m (NH4Cl), 0.8-1.5 mu m (HCl) and 0.2-0.5 mu
m (H2SO4). The influence of the generating conditions on the size and
the concentration of the aerosol particles have been investigated. Aft
er the generation, the particles were exposed to atmospheres of differ
ent relative humidity. If a certain level of relative humidity is exce
eded, the solid salt particles dissolute and become droplets. The part
icle diameter of the salt and acid droplets increases if the relative
humidity is raised. The particle diameters and concentrations were mea
sured to show the dependence on the generating conditions and the rela
tive humidity by a laseroptical extinction technique. The results of t
he measurements were compared with growth models. There was a very goo
d agreement between the experimental data and the growth models for sa
lt and acid aerosols. It is therefore possible to evaluate the limit o
f the growth by pure water vapour saturation, which is especially usef
ul for the design of particle separators.