Portable instrument for online investigations of optical properties of airborne particles

Abstract

For the development of photoelectric fire detectors the discrimination of smoke from nuisance aerosols is still one of the main goals. In order to improve our understanding of optical properties of airborne particles and to determine different quantities like morphology, efractive index or size distribution, a time resolved online measurement instrument is highly advantageous. The presented instrument measures fourteen scattering vectors at two wavelengths and two different polarization directions of the incident light. Main effort was put on achieving high stability and high dynamic range by carefully designing the optics and exploiting a wide measurement range of the detectors. As a result the dynamic range is improved by approximately a factor of three (compared to [1]). The time resolution has been increased by a factor of two although the number of measured polarization states has been doubled. A fast and field-capable calibration method was developed, enabling for a quick set-up in the field, while keeping the accuracy as close as possible to the laboratory conditions. Scattered light and particle size distribution measurements with Di-Ethyl-Hexyl-Sebacat (DEHS) aerosol were performed and compared to Mie scattering calculations in order to verify the calibration. As a next step a comprehensive data base of aerosol optical properties including polarization dependent scattering will be collected serving as a basis for designing novel fire detectors.