The Application of Condensation Nuclei Monitors to Clean Rooms

The instrument often used by aerosol researchers to detect 0.1-μm and smaller particles is the condensation nuclei monitor. The instrument will provide information about ultrafine particles in the clean room unobtainable by any other means. The principle of operation is to grow the particles by the condensation of water or alcohol onto a size that can be detected optically. The instrument was invented at the turn of the century by John Aitken.¹ His instrument was an adiabatic expansion chamber followed by counting with a microscope after the droplets had settled onto a slide. In the last few years, automatic instruments have been commercially available. Since the condensation nuclei counter only detects the total number of particles, a particle size preseparator needs to be used with the instrument to obtain size distribution information. One type of preseparator is the "diffusion battery," and another is a differential mobility separator. The present application of the instrument is as a research tool to quantify the size spectrum of particles less than 1 μm. Measurements of clean-room condensation nuclei will be presented under a number of situations.