Morphology and Fractal Dimension of Size-Resolved Soot Particles Emitted From Combustion Sources

The complex morphology of soot particles causes uncertainties in simulating their optical effects in the atmosphere. By applying a new image recognition technique based on electron microscope observations and field studies, we set up a database that displays the mixing state, effective density (ρ_eff), monomer number and diameter (N and d_p), and fractal dimension (D_f) of size-resolved soot particles freshly emitted from vehicle emissions (VE), biomass burning (BB), coal combustion (CC), tunnel air (TA) and urban air (UA). We determined that freshly-emitted soot particles from combustion sources contain not only bare-like soot but also some coated-soot particles. ρ_eff (157 - 689 kg/m³) decreased while N (46 - 1500) and d_p (24 - 42 nm) increased with the increased diameter of soot particles. The D_f of BB and CC were independent of the diameter changes and fluctuated between 1.65 and 1.80, while the D_f of VE and TA (1.62 - 1.71) increased and UA D_f (1.87 - 1.80) decreased with increasing diameter. This study highlights that the morphological parameters of freshly-emitted soot particles vary among different combustion sources and have a size effect, particularly for finer and coarser soot particles. The database of size-resolved soot particles will be helpful to improve soot models based on numerical simulation and better evaluate atmospheric optical properties.

Figure 1. Relationship between diameter and (a) effective density (ρ_eff); (b) number of monomers (N); (c) monomer diameter (d_p); and (d) fractal dimension (D_f). Each color represents one source. The value in the rightmost columns of each figure represents the average values of soot particles in all size bins: vehicle emissions (VE), biomass burning (BB), coal combustion (CC), tunnel air (TA) and urban air (UA). The soot particles <150 nm from CC and >600 nm from TA were extremely low; therefore, we do not show the data. The error bars represent 90% confidence intervals.

Title：

Pang, Y., Chen, M., Wang, Y., Chen, X., Teng, X., Kong, S., Zheng, Z., Li, W., 2023. Morphology and Fractal Dimension of Size-Resolved Soot Particles Emitted From Combustion Sources. Journal of Geophysical Research: Atmospheres 128 (6), e2022JD037711.