Optical Methods for Measurement of Concentration, Size Distribution and Refractive Index of Airborne Particles

The knowledge of airborne particle sizes and concentrations together with optical properties is frequently needed to assess their environmental burden. Here intensity based optical techniques are discussed allowing an in-situ, real-time particle sizing and counting starting from about 10-1μm particle radius. Combining the optical measurement with a droplet condensational growth in controlled vapor supersaturation levels provides an access to the size distribution information of nuclei particles in the size range below 0.1μm based on Kelvin equivalent sizing extending particle counting and sizing to about 10-3μm in radius. Measurements based on a simultaneous detection of scattered and transmitted light fluxes from droplets growing in supersaturated vapors resulting in an absolute determination of particle number concentrations are presented. The results show that optical methods introduced here provide an accurate description of aerosols in the size range starting at about 10-3μm in radius with a span over about 4 orders of magnitude and concentrations starting from single particle counting range up to 108 cm-3. Finally new optical arrangements are introduced and their potential to infer the refractive index of a particle from light scattering and propagation measurements is discussed.