Aerosol particles dispersed by nebulization, combustion, or powder dispersion are usually electrostatically charged. For effective transport and for instruments that operate on an electrostatic principle, such aerosols must be properly conditioned.

TSI Aerosol Neutralizers use a radioactive source (Kr-85 or Po-210) to perform this function. The radioactive source ionizes the surrounding atmosphere into positive and negative ions. Particles carrying a high charge can discharge by capturing ions of opposite polarity. After a short time, the particles reach charge equilibrium such that the aerosol carries a bipolar distribution.