Multi-angle, dual wavelength scattering measurement chamber for the structural measurement of combustion generated particles

Abstract

Soot particles are formed through combustion processes and have fractal-like shapes. They influence our climate by absorption and scattering of the solar radiation directly, and indirectly by their influence on cloud (liquid or glaciated) formation and their deposition on snow and ice surfaces. An Instrument, which we would like to introduce in this paper was developed and built at the University of Applied Sciences Northwestern Switzerland to measure light scattering properties of combustion type aerosols. A closed chamber was designed where the scattered light can be detected at 7 fixed, predefined angles simultaneously. Two lasers at 405nm and 852nm serve as light sources, and with that almost simultaneous measurements at the two different wavelengths can be carried out. The instrument is calibrated with aerosol particles of known scattering properties and concentration. We used nebulized, size selected ammonium sulphate particles for this purpose.The angular light scattering is influenced by the shape of the particles. In the case of fractals information on the fractal dimension and characteristic size can be derived from the angle dependence of the scattered light. In this paper we demonstrate and test the performance of this new light scattering instrument through the measurement of different soot or soot–containing aerosols. These examples include the measurement of artificial soot particles generated by two different soot generators (Cast soot and Palas soot generators) and different kind of combustion produced aerosols like: flaming ethanol, smouldering wood and mixed smouldering/flaming wood smokes.