An Innovative Approach to Optical Measurement of Atmospheric Aerosols—Determination of the Size and the Complex Refractive Index of Single Aerosol Particles
As a result of the intrinsic nature of elastic light scattering aerosol particles, the non-monotonic size dependence of the scattered light intensity infl uences the function of most single optical particle counters and spectrometers. In order to tackle the problem of the varying response of single particle spectrometers when refractive indices of aerosol change, we developed a system utilizing two laser illumination sources with different wavelengths (533 nm and 685 nm) and four detectors collecting the forward and backward scattered light from both illuminating beams. The new method aims to determine the size and refractive index of particles typically occurring in the atmosphere. We successfully tested this new method numerically for its capability to simultaneously determine particle size in the range from 0.1 to 10 μm, the real part of the refractive index spanning from 1.1 to 2, and the imaginary part of refractive index between 0 and 1. The fi rst experimental results obtained with the prototype of the spectrometer verify the capability of the technique for accurate size measurement and real-time differentiation between non-absorbing and absorbing aerosol particles.
Keywords: Atmospheric aerosols, optical measurement, particle size, refractive index
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