Aerodynamic particle size measurement by electrodynamic oscillation techniques

Four dynamical techniques for measuring the aerodynamic size of spherical a nd nonspherical aerosol particles are evaluated and compared. For spheres t he classical method of angular light scattering is also included. One metho d based on particle dynamics, the so-called springpoint method has been ext ensively used, but the other particle oscillation methods have been used ra rely or not at all. All the dynamical methods involve imbalancing a particl e in an electrodynamic balance (EDB) by changing the de potential to produc e particle oscillation. A linescan CCD camera and associated electronics we re used to measure the amplitude of the oscillations, the offset of oscilla tion centers, and the phase lag relative to the ac drive. These measurement s are compared with theoretical solutions of the equation of particle motio n to establish the aerodynamic size of the particle. The stability characte ristics of the particle are analyzed by solving the particle equation of mo tion using the method of continued fractions. The Various techniques are co mpared for spheres, spheroids and crystalline or amorphous particles of irr egular shape. All five methods are shown to be in good agreement for sphere s (within 3.9%). For non-spherical germanium dioxide particles the three os cillation methods agree with the springpoint method within 3.4%. (C) 2000 E lsevier Science Ltd. All rights reserved.