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Atmospheric and Oceanic Optics

2014 year, number 1

Optical and microphysical properties of the mixed smoke according to the polarization spectronephelometric measurements

R.F. Rakhimov, V.S. Kozlov, A.G. Tumakov, V.P. Shmargunov
V.E. Zuev Institute of Atmospheric Optics of Siberian Branch of the Russian Academy of Science, 1, Academician Zuev square, Tomsk, 634021, Russia
Keywords: mixed smoke, polarization spectronephelometry, inverse problem, particle’s size distribution, complex index of refraction, soot


A polarization spectronephelometer was used for measurements of spectral coefficients of angular aerosol scattering in mixed smokes during their 3-day evolution in the Large Aerosol Chamber of IAO SB RAS (1800 m3). The smokes were formed as a mixture of products of thermal decomposition of coniferous wood materials (pine) from sources of low-temperature pyrolysis (~ 400°C) and high-temperature open combustion with flame (~ 800°C). The inverse problem was solved to study peculiarities in formation of the disperse composition of smokes and the complex refractive index of smoke particles for three size ranges. It is shown that the dynamics of formation and evolution of mixed smokes is determined mostly by the contribution of the strongly absorbing ultra-fine fraction (particle radius of < 150 nm, the imaginary part of the refractive index of particulate matter of ~ 0.4–0.8 close to that of black carbon) to the optical properties. Medium and coarse particles (radius of > 200 nm) are moderately and weakly absorbing: the imaginary part of refractive index is ~ 0.03–0.15. The absorptivity of mixed smoke is high, and the single scattering albedo at the wavelength 525 nm achieves low values of ~ 0.60–0.45, decreasing during the smoke storage. At the smoke generation, bimodal particle size distributions with the medium of 350–400 nm and coarse of ~ 760 nm modes are formed. After long storage of the smoke, the particle size spectrum is characterized by a single mode of ~ 600 nm, and the effective radius of the particles increases from 160 nm to 330 nm. It is shown that the mutual dynamics between the volume backscattering and extinction coefficients, single scattering albedo and effective radius of particles are described by statistically significant linear correlations.