The features of dynamics of the complex refractive index (CRI) for three particle fractions during two days aging of the mixed wood smoke were studied. Smokes were generated due to simultaneous emissions of particles from the two sources in the regimes of pyrolysis and flaming combustion. At the initial stage the imaginary refractive index of the particles decreases of about 600 times with transition from micro- to coarse-dispersed particles. In the long-term aging of smoke (1-2 days) ? decreases for micro-dispersed soot particles (by 1.2 times), but is increased for middle- and coarse-dispersed particles by 1.5 and 4.7 times, respectively. This means that the microphysical dynamics of mixed smokes at all stages of its existence is determined by the penetration of soot from the ultra-fine size range to the region of larger particle sizes due to coagulation. Numerical experiment has shown that for correct solution of the inverse problem during the aging of mixed smokes one must use only CRI values corresponding exactly to each fixed time moment. Attempts to solve the inverse problem using some constant CRI values over all time period lead to an increase of the discrepancy between the measured and the reconstructed optical characteristics by about several times with respect to the residual of about 6-10% corresponding to the true values of CRI. Verification of the 3-fractional approach to solution of the inverse problem was carried out by using dispersed aerosol with a known CRI value (ethylene glycol). This testing showed that the technique developed provides the accurate reconstruction of the value of CRI for the main optically active fraction of middle-dispersed particles. Use of the 3-fractional method has allowed one to reduce the inverse problem residuals on average by a half compared to the traditional 1-fractional method for homogeneous particles.
biomass burning, mixed smokes, soot, spectronephelometry, inverse problem, size distribution, complex index of refraction, temporal variability