BEHAVIOR OF ULTRAFINE PARTICLES GENERATED FROM ORGANIC VAPORS BY CORONA IONIZERS

This paper reports an experimental study on the stability, coagulation and diffusion of molecular clusters and ultrafine particles generated from organic vapors by corona ionizers. Upon leaving the ionizer, par ticles are made to flow within several types of vessels: depending on the specific geometry of the flow system, clusters either coagulate in to large particles or are deposited on the walls. Particles larger tha n 4 nm and molecular clusters penetrate through a wire-screen type dif fusion battery, but particles in the size range between 2 and 4 nm are collected. Among the organic compounds tested (aromatics, alcohols, k etones and others), only aromatic compounds appear to yield unstable c lusters which grow into detectable particles (>2 nm) through Brownian coagulation. The other compounds either do not undergo the gas-to-part icle conversion process or are too small to be detected. Furthermore, the presence of moisture seems to be of fundamental importance in the particle generation phenomenon. The addition of alcohols to the vapor mixture inhibits particle formation.