Variations in Condensation Properties of Mixed Smoke from Biomass Burning at Different Smoke Evolution Stages

Abstract

The variations in the optical-microphysical properties of the mixed wood smoke are studied in the Large Aerosol Chamber, Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences (volume of 1800 m3) during long-term (6-day) smoke aging under the conditions of periodic impacts of relative air humidity varying in the range 45–95%. Spectral nephelometric measurements of angular scattering and solution of the inverse problem were used to analyze the dynamics of the size distributions and complex refractive indices for ultrafine, medium-sized, and coarse fractions of particles, as well as effective particle radius, lidar scattering parameter, and single scattering albedo in the visible spectral range. It is found that both quantitative and qualitative features of the variations in the aerosol optical-microphysical parameters substantially change at different smoke aging stages as functions of air humidity. It is shown that, during aging of the mixed smoke, the key factors of the variations in smoke properties are the physical-chemical heterogeneity of three fractions of smoke particles, as well as the physical processes of coagulation migration of ultrafine black carbon particles (<100 nm in size) across the size spectrum and the condensational wetting of smoke particles. The interrelated effect (“interference”) of these processes on the particle structure determines the main features of the dynamics of the disperse composition and absorption properties of smoke particles.