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Atmospheric and Oceanic Optics

2013 year, number 12

Optical and microphysical properties of the pyrolysis smoke from measurements by the use of the 4-wavelength polarization spectronephelometer

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: pyrolysis smoke, polarization spectronephelometry, inverse problem, particle’s size distribution, complex index of refraction


Data of polarization spectronephelometric measurements have been used to study the dynamics of optical-microphysical properties of pyrolysis smoke during three days of smoke aging in the Large Aerosol Chamber of IAO SB RAS (1800 m3). The smoke was formed from low-temperature (~ 400 °C) decomposition of wood of coniferous trees (pine). The inverse problem was solved to study peculiarities in the disperse composition and the complex refractive index of smoke particles. A key difference of the microphysics of pyrolysis smokes from mixed regimes of forest biomass burning is the low content of strongly absorbing compounds (black carbon) in ultra-fine particles (radius < 150 nm). As a result, the smokes are weakly absorbing, and the single scattering albedo of dense pyrolysis smoke in the visible spectral region (~ 525 nm) at the stage of smoke formation is close to 1 and decreases after 3-day storage down to only ~ 0.96. In the size distribution of particles, the medium (~ 400 nm) and coarse (~ 850 nm) fractions are formed. At the smoke aging, the both modes shift toward smaller sizes, and for the aged smoke the medium fraction becomes the main mode in the size spectrum. The pyrolysis smoke, in contrast to mixed smokes, is characterized by the wide size spectrum up to radii of about 1500 nm. As a consequence, the effective radius of pyrolysis particles (~ 400 nm) at the smoke formation is more than twice as large as that of mixed smokes. At the smoke aging, the effective radius decreases from 400 to 170 nm. Stable correlations have been found between the volume coefficients of lidar scattering and extinction, albedo and effective radius of particles. These correlations count in favor of applicability of the single-parameter model of submicron aerosol for the pyrolysis smoke.