Refractive Index and Size Distribution of Aerosols as Estimated from Light Scattering Measurements

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  • 1 Upper Atmosphere Research Laboratory, Tohoku University, Sendai, 980 Japan
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Abstract

Angular distributions of the intensity of light scattered by airborne particles were measured for both parallel and perpendicularly polarized components. A precision polar nephelometer was constructed for use of this study. The data were analyzed using a newly developed inversion library method to give a simultaneous estimate of the complex index of refraction m = mrmii of aerosols and their size distribution, where mr is the real part and mi the imaginary part of the refractive index. Results of 302 measurements show that the monthly mean values of mr and mi vary within the range 1.47–1.57 and 0.009–0.037, respectively, depending upon the relative humidity.

The size distribution of aerosols can be approximated by the log-normal distribution function; the mean radius and the standard deviation are found to be rg = 0.138 μm and σg = 2.56, respectively, as geometrical mean values for the whole data.

Abstract

Angular distributions of the intensity of light scattered by airborne particles were measured for both parallel and perpendicularly polarized components. A precision polar nephelometer was constructed for use of this study. The data were analyzed using a newly developed inversion library method to give a simultaneous estimate of the complex index of refraction m = mrmii of aerosols and their size distribution, where mr is the real part and mi the imaginary part of the refractive index. Results of 302 measurements show that the monthly mean values of mr and mi vary within the range 1.47–1.57 and 0.009–0.037, respectively, depending upon the relative humidity.

The size distribution of aerosols can be approximated by the log-normal distribution function; the mean radius and the standard deviation are found to be rg = 0.138 μm and σg = 2.56, respectively, as geometrical mean values for the whole data.

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