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

Abstract

Databases of the morphological parameters of fresh size‐resolved soot particles and their systematic comparisons among various combustion sources are important to trace the soot aging process and evaluate their optical properties. Here, the mixing state, effective density (ρeff), monomer number and diameter (N and dp), and fractal dimension (Df) of size‐resolved soot particles from vehicle emissions (VE), biomass burning (BB), coal combustion (CC), tunnel air (TA) and urban air (UA) were characterized based on electron microscopy observations and analysis. We determined that freshly‐emitted soot particles from combustion sources contain not only bare‐like soot but also some coated‐soot particles. ρeff (157–689 kg/m3) decreased while N (46–1,500) and dp (24–42 nm) increased with the increased diameter of soot particles. The Df of BB and CC were independent of the diameter changes and fluctuated between 1.65 and 1.80, while the Df of VE and TA (1.62–1.71) increased and UA Df (1.87–1.80) decreased with increasing diameter. Based on Df obtained in this study, we found that the ensemble Df of VE, BB, CC, TA, and UA could not represent the finer (<150 nm) soot particles and coarser soot particles (>600 nm) in VE, TA, and UA. 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.

Quantification and Characterization of Fine Plastic Particles as Considerable Components in Atmospheric Fine Particles

“…In contrast, tar balls are easily recognized by their spherical morphology (site 3 in Figure 2a), which is a result of gas-to-particle transformation followed by condensational growth on primary biomass burning particles. 41 Soot contains small spherules that form fractal-like chain structures ranging in size from nanometers to a few micrometers 42 (site 4 in Figure 2a).…”

Microphysical properties of atmospheric soot and organic particles: measurements, modeling, and impacts

“…It is generally assumed that the type of combustion source soot particles exerts discernible impacts on soot particles' fractal morphology. Recent studies have underscored the differences in morphological parameters of freshly emitted soot particles originating from different combustion sources, in particular for finer and coarser sizes of soot particles 71,77 . Additionally, many studies reported significant changes in the D f values related to the atmospheric ageing processes.…”

“…Two primary categories of light-absorbing carbonaceous particles are recognized as BC associated with soot and BrC associated with the light-absorbing components of POA and SOA. Over the past decade, significant advances have been made in utilizing the fractal dimension D f to quantitatively assess the morphology and mixing structure of soot particles 52,56,71,73,74,77 . Furthermore, practical parameterization schemes have been developed to incorporate these parameters into atmospheric modeling to better understand how the ageing process of soot impact its optical absorption within the atmosphere 13,38,103,104 .…”

Distribution and Fractal Characteristics of Outdoor Particles in High-Rise Buildings Based on Fractal Theory

“…Fractals were originally introduced by Mandelbrot to describe the fractal behaviors of similar geometries in disordered and irregular objects [27], such as coastlines [28], porous media [29], and biological structures [30]. Fractal theory also can be used to describe the irregular sizes and shape distributions of atmospheric particles [31][32][33][34]. It has the unique advantage of describing the different condensed states, shapes, and distribution of the particles in the environment [31], such as through using the fractal dimension to describe the morphology and size of combustion soot particles [32], the fractal description of finely ground particles of natural quartz using the particle size [33], and the expression of the spray agglomeration of polymer particles [34].…”

“…Fractal theory also can be used to describe the irregular sizes and shape distributions of atmospheric particles [31][32][33][34]. It has the unique advantage of describing the different condensed states, shapes, and distribution of the particles in the environment [31], such as through using the fractal dimension to describe the morphology and size of combustion soot particles [32], the fractal description of finely ground particles of natural quartz using the particle size [33], and the expression of the spray agglomeration of polymer particles [34]. Fractal theory and fractal parameters can provide more accurate descriptions of particle morphology, which can provide specific numerical representations for irregular descriptions.…”