Sensitivity of mixing states on optical properties of fresh secondary organic carbon aerosols

摘要

At the beginning of the interaction of black carbon (or soot) and organic particles, fresh secondary organic carbon aerosols are generated by the dominant fractal aggregated soot monomers and the slight organic coatings. The complex morphologies and mixing states of these fresh secondary organic carbon aerosols significantly influence their optical properties. In this study, these heterogeneous particles were reconstructed using the fixed volume fraction model, and their optical properties are calculated using the discrete dipole approximation (DDA) method. For soot particles aged in a short time, the simulated absorption, scattering and single scattering albedo (SSA) showed a good agreement with the measurements. The amplifications of absorption and scattering between the thinly coated states (soot volume fraction equals 0.8, or the shell/core diameter ratio equals 1.08) and the freshly emitted states (bare soot with soot volume fraction equals 1) can reach to similar to 15% and similar to 35%, respectively. The simulations with these thinly coated states also indicated that the variations of morphologies may lead to the significant relative deviations on the absorption (up to similar to 15%) and scattering (up to similar to 100%) of these secondary aerosols. The effects of soot compactness and size on their optical properties were sensitive to the thickness of organic coatings, and larger organic refractive index may lead to larger absorption enhancements. (C) 2017 Elsevier Ltd. All rights reserved.