A new method for the simultaneous measurement of aerosol particle size, complex refractive index and particle density

Particle size measurement by means of optical spectrometry of single particles depends substantially on the angular range of light scattering and the refractive index of the particle. Knowledge of the latter determines implicitly the accuracy of measurement. In contrast to commonly used instrumental systems the configuration of the design concept presented here consists of two laser illumination sources with different wavelengths and four angular ranges for the collection of scattered light. As a result a set of four independent pulses from each measured particle can be obtained allowing simultaneous assessment of particle size and its complex refractive index. Based on the Mie theory of light scattering, light collection angles yielding a single-valued aerosol size measurement were identified and used to design a new optical system. Based on the modelling of the performance for an assumed instrumental arrangement the sizing errors were found to be about 2%. The accuracy of assessment of the complex index of refraction was found to be of the order of 10% over the range of particle diameters investigated (0.1-10 mum). The theoretical results show clearly the capability of this novel instrumental design for the measurement of aerosol particle sizes, their density and optical properties. Based on these model calculations an experimental set-up is under construction.