Photochemical Aging Induces Changes in the Effective Densities, Morphologies, and Optical Properties of Combustion Aerosol Particles

Effective density (peff) is an important property describing particle transportation in the atmosphere and in the human respiratory tract. In this study, the particle size dependency of peff was determined for fresh and photochemically aged particles from residential combustion of wood logs and brown coal, as well as from an aerosol standard (CAST) burner. peff increased considerably due to photochemical aging, especially for soot agglomerates larger than 100 nm in mobility diameter. The increase depends on the presence of condensable vapors and agglomerate size and can be explained by collapsing of chain-like agglomerates and filling of their voids and formation of secondary coating. The measured and modeled particle optical properties suggest that while light absorption, scattering, and the single-scattering albedo of soot particle increase during photochemical processing, their radiative forcing remains positive until the amount of nonabsorbing coating exceeds approximately 90% of the particle mass.

Automated summary

In this study, the particle size dependency of the effective density (peff) was investigated for different types of particles from residential combustion and an aerosol standard burner. It was found that peff significantly increased due to photochemical aging, especially for larger soot agglomerates. The increase can be explained by the collapsing of chain-like agglomerates, filling of voids, and formation of secondary coating.