Rein Andre Roos

An instrument for measuring electric chargeon individual aerosol particles

Abstract An apparatus has been developed for measuring charge on Individual aerosol particles. The apparatus is based on a method described by Gajewski (1984) . Preliminary experiments have been done with glass beads of different sizes (in the size range>200,μm). The results of these preliminary experiments prove that the apparatus works well and that it can be used for much smaller particles.

Photon correlation spectroscopy for analysis of low concentration submicrometer samples

Photon Correlation Spectroscopy is a technique to rapidly measure particle size in the submicrometer region. The use of PCS is, however, limited by concentration. The upper limit is due to multiple scattering of the incident light, the lower limit is determined by the fact that fluctuations of the number of particles in the measuring zone have a significant influence on the apparent diffusion coefficient. In this article a new signal processing method is described which differentiates this influence. With this system the lower limit is no longer limited to about 100 particles in the measuring volume corresponding to a concentration of 109 particles/cm3. The limitation is now the intensity of the scattered light which becomes too weak at a concentration of about 50 particles/cm3. As a consequence of this work, a revision to the basic theory of PCS may be necessary. Moreover, the new processing method enables also the measurement of particle concentration in the sample.