the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Disparate evolution mechanisms and optical absorption for transboundary soot particles passing through inland and sea pathways
Abstract. Soot particles, as a type of warming aerosols, play a critical role in climate warming. During transport, these particles undergo atmospheric condition-dependent aging processes that influence their microphysical and optical properties. Here, we investigated the variations in morphology, mixing states, sizes, and optical absorption of soot-containing particles and further revealed their evolution mechanisms during two distinct transboundary transport through the inland and sea pathways. Comparing transboundary soot-containing particles transported through the inland and sea pathways, we found more soot cores in the latter individual particles, although their dominant mixing states exhibited a similar transition from partly-coated at 62–67 % by number to embedded structures at 71–72 %. The core-shell size ratio (Dp/Dc) and soot core fractal dimension of embedded soot-containing particles transported through the sea pathway were both greater compared to the inland pathway. These differences were attributed to distinct evolution mechanisms experienced by soot-containing particles during transport: heterogeneous aging processes through the inland pathway and cloud processes through the sea pathway. Optical simulation showed amplified light absorption of soot-containing particles during their transboundary transport. Furthermore, the radiative absorption amplification per unit Dp/Dc change reduced by 72 % due to the entrainment of multiple soot cores within individual particles following the transport pathway change from the inland to the sea. This study suggests varied mixing configurations and radiative absorption of transboundary soot-containing particles driven by different environmental conditions and highlights the necessity of incorporating multicore black carbon mixing structures into climate models.
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Status: open (until 13 Nov 2025)
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RC1: 'Comment on egusphere-2025-3878', Magin Lapuerta, 20 Oct 2025
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- General comment: This is an interesting work, based on the observation of different patterns in aerosols associated with different wind trajectories. However, some clarifications are needed. Section 3.4 about optical absorption should be revised. Although English is good in general, grammar should be revised. Notation is not always defined or is not self-consistent. Structure (main manuscript/SM) should also be revised.
- Specific comments: Segregation of information into the Supplementary Material should be done when this information is not essential for understanding the study. In this case, the information in the SM is essential to follow the main manuscript. Authors are suggested to reorganize the information.
- Introduction: This reviewer does not agree with some conventions often used in environmental articles, such as the equivalence between black carbon and elemental carbon (BC is a carbonaceous combustion-derived aerosol, while elemental carbon is the major chemical component of BC, but also of any organic material), or the list of soot sources (why fossil fuels and biomass??; any liquid biofuel, electrofuel, or non-biologic waste material will also emit soot when burned).
- Introduction: This reviewer does not agree that “simulating soot climate effect is readily achievable in models”, as stated. The variety of sizes, shapes, compositions, and nanostructures affect the optical properties of soot and makes the simulation very difficult.
- Section 2.2: If OM/OC ratios in Chinese cities is assumed as 1.91, what organic matter is the remaining 0.91/1.91? Why
- Sections 2.2 and 3.2: TEM operates under high vacuum. Therefore, evaporation or sublimation of coatings could occur even in “conventional TEM observations”. What is the change in the beam power to distinguish between “enhanced electron beam observations” and “conventional observations”, and thus between enhanced and conventional absorption? Could authors include TEM images of the same particle before and after enhancing the beam power? Visible bubbles observed in Figures 3 and 4, indicating evaporation, are declared to correspond after enhancing power, but how do these particles look like before? Are diameters “Dp” those obtained with TEM under conventional mode and “Dc” those obtained under enhanced electron beam? Please clarify.
- Sections 2.2 and 3.2: What do authors exactly mean by “mixing states” of soot particles? Is it an appropriate name? Based on Text S1, it seems that they refer to chemical composition. However, based on Section 3.2 and Figures 3 and 4, it seems that they refer to bare-like, partly-coated or embedded. Please correct or clarify.
- Section 2.2: Equations 4 to 7 are written without a brief explanation of their meaning. Authors should at least explain that ignoring the overlap (or sintering or interpenetration) between monomers would lead to underestimation of the fractal prefactor of the power-law relationship (eq. 4). Moreover, publications after 1997 have demonstrated that also this prefactor (not only that in eq. 5) is highly affected by the overlap parameter (see, e.g., Powder Technology 271, 141–154 (2015)).
- Section 2.3: Parameters “n” and “W” in equation 9 are not defined. Please check uniformity in the notation.
- Section 3.1: In Figure S4 the content in EC (supposedly associated with soot) is very minor (purple). On the contrary, in Figure S5, the percent of soot-containing particles is very high (light blue). How do these results match?
- Section 3.3: What is, in the opinion of authors, the dominant reason for the increase in the size, the number of soot cores, the Dp/Dc ratio, and the fractal dimension of soot structures: coalescence between agglomerates (entrainment) or breakage of agglomerates inside the aerosol (collapse)?
- Section 3.4: This reviewer can understand that the energy adsorbed is reduced for the sea pathway with respect to the inland pathway, and even that multiple cores may also contribute to reduce absorption. But does not understand why the energy absorbed from embedded particles is higher than that absorbed from soot cores (Figure 10a). The refractive index of soot is much higher than that of coatings (and specially its imaginary part, related to attenuation of light). Consequently, the ageing process should lead to a decrease in the energy absorbed. Please, revise, or explain better.
- Technical corrections: please correct “If the high-pressure system located” to “If the high-pressure system is located”; “Obviously, there was a bench of data” to “Obviously, there is a bench of data”; “However, transboundary haze pollutants crossed the East China Sea remain unexplored” to “However, transboundary haze pollutants crossing the East China Sea remain unexplored”.
ReplyCitation: https://doi.org/10.5194/egusphere-2025-3878-RC1
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