A series of smoke generation experiments in the Big Aerosol Chamber was carried out. Changes in particle size distribution and complex parameter of refraction (CPR) were studied under the growth of temperature of thermal decomposition of wood samples. The pyrolysis wood decomposition under temperature growth (from 350 up to 700°С) leads to a decrease of relative share of middle-size (0.3 < r < 0.8 microns) and large particles with r > 1 micron. As the temperature increases from 590 to 700°C, the relative share of absorbing formations grows. The real part of the CPR varies from 1.59 to 1.7, while the imaginary part changes from 0.005 to 0.020. At the final stages of pyrolysis size spectra become closer, and their volumetric distribution degenerates in the unimodal form of logarithmically normal distribution with the effective size ref ≈ rm ≈ 0,3 microns and the width of dispersion parameter 2ln2σ ≈ 1/12. At a relatively low temperature (Т ~ 300 °С), the incomplete decomposition of coniferous wood is observed. This smoke exceeds high-temperature smokes in integral volume and particles sizes.