the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 21 May 2025
Individual particle compositions and aerosol mixing states at different altitudes over the ocean in East Asia
Abstract. Aerosol composition and mixing state influence its ability to form cloud droplets and ice crystals and to scatter and absorb sunlight, all of which affect its impact on climate. In this study, aerosol samples were collected over the ocean in the western North Pacific at different altitudes from the sea surface to ~8000 m using an aircraft and a research vessel in the summer of 2022. During the campaign, we had samples originating over the ocean, desert, Siberian Forest biomass burning event, and other sources in East Asia. These samples were classified into three periods based on the sampled air parcel sources and particle compositions measured using transmission electron microscopy. Samples from period 1 had high sea salt and mineral dust fractions, while in period 2, the samples had high fractions of potassium-bearing particles with organics and black carbon concentrations, indicating that they originated from a Siberian Forest biomass burning event. The samples from period 3 showed influences of both sea spray and biomass burning. The number fractions of aerosol types also varied depending on particle size and sampling altitude. Compositions of biomass burning and sea spray were mixed at individual particles and the extent of their mixtures depended on the sampling periods and altitudes. Our results showed a wide range of particle compositions and mixing states, which vary with aerosol source, size, and altitude. These factors need to be considered when evaluating aerosol composition and mixing state, both of which affect aerosol climate effects.
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RC1: 'Comment on egusphere-2025-2230', Anonymous Referee #1, 07 Jun 2025
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This manuscript presents a comprehensive analysis of individual aerosol particle compositions and mixing states collected over the western North Pacific during summer 2022, utilizing coordinated aircraft and research vessel measurements. The authors employed transmission electron microscopy with energy dispersive X-ray spectrometry (TEM-EDS) to characterize aerosol particles from sea surface to approximately 8000 m altitude. The study identifies three distinct periods based on air mass origins and demonstrates how particle compositions vary with size, altitude, and source regions, providing valuable insights into aerosol mixing states at the individual particle level. However, several aspects of the manuscript require improvement, as detailed below.
- The Abstract should more precisely articulate the major findings and conclusions of the study.
- The introduction should better emphasize the significance of aerosol particle composition, size distribution, and mixing state in climate impacts.
- The introduction and discussion sections would benefit from more detailed information and comparative discussion of aerosols at different altitudes, including specific quantitative values of their influence, which would enhance the paper's impact.
- Regarding Figure 3d and 4c-d: The elemental mapping images show ubiquitous weak Na signals covering almost the entire mapping area. Is this Na derived from combustion processes?
- In the supplementary materials, particles are classified as K-bearing when K > 0.01 wt%. Did you perform EDS analysis on every individual particle in the samples?
- Lines 316-325: When discussing BC between 1 and 3 km, it is essential to elaborate on the climate implications, particularly the effects at higher altitudes (Lohmann et al., 2020; Wang et al., 2025).
- Line 240 states: "In addition, some increases in sea salt were observed in samples from > 7000 m, which could be due to long-range transport." This explanation lacks clarity. What specific mechanisms of long-range transport would increase sea salt concentrations above 7000 m? Are sea salt particles more susceptible to high-altitude transport compared to other aerosol types?
- The manuscript would benefit from more comprehensive comparison with previous single-particle studies in the region. How do the observed mixing states compare with other studies over the North Pacific? Are the biomass burning signatures consistent with other Siberian fire events? How do the mineral dust characteristics compare with known Asian dust compositions?
- As mentioned earlier, while addressed in the conclusions, the climate implications could be expanded to include: specific discussion of how the observed mixing states affect optical properties; implications for ice nucleation and cloud condensation nuclei activity; and relevance for model parameterizations.
References:
Lohmann, et al. (2020). Future warming exacerbated by aged-soot effect on cloud formation. Nature Geoscience, 13(10), 674-680. https://doi.org/10.1038/s41561-020-0631-0
Wang, et al. (2025). Improved representation of black carbon mixing structures suggests stronger direct radiative heating. One Earth, 8(5), 101311. https://doi.org/10.1016/j.oneear.2025.101311
Citation: https://doi.org/10.5194/egusphere-2025-2230-RC1 -
RC2: 'Comment on egusphere-2025-2230', Anonymous Referee #2, 10 Jun 2025
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Adachi et al. presented a comprehensive single particle analysis of aerosols collected at different altitudes over the western North Pacific Ocean. This work provides valuable insights into the source and composition of aerosols in East Asia, which are not yet fully understood. Overall, this study is well-designed, and the paper is well-written. There are some places where I have some comments. Please see my comments below.
General comments:
- I have some questions about the particle classification matrix. First, how did you develop the matrix? Based on the literature or K-means cluster? Secondly, it seems like the classification can lead to conditions where particles can be classified into multiple classes (e.g., a particle with Al > 0.5 wt%, Si > 2 wt%, Na >1 wt%, and Mg > 0.01 wt% can be classified into both mineral dust and sea salt classes). Could you double-check your flow chart? Is that because you did not list the criteria to exclude particles from other classes (e.g., mineral dust should be Al > 0.5 wt% and Si > 2 wt% and Na <1 wt%, Mg < 0.01 wt%, K < 0.01 wt%, Ca < 0.5 wt%, S < 1 wt%, C+O < 90 wt%)? If yes, please add a note to make this clear to audiences.
- Section 2.6 needs to provide more information to help people reproduce the results.
- I suggest adding some labels in the TEM images to indicate different types of particles.
- L 249-250, “In figure 7a …. Along with their sampling altitudes.” I am not sure Na/(Na+K) is a good proxy for sea salt mixed with biomass burning aerosol, since biomass burning also emits trace amounts of Na, and sea salt also contains some K. The K salt typically has lower solubility than Na salt, so they will crystallize first before Na salt and from individual K salt particles. Could you please add some discussion about this?
- Could you add Si maps to help identify the mineral dusts? It will be useful to support Figure 8 particle is a dust since Ca, Mg, and CO3 can exist in marine
Specific comments:
- L100-103, “Second, we selected … (STEM-EDS).” Could you explain a little bit more about the criteria you used to select the representative area? Moreover, does “6,000 X” mean magnification of 6,000?
- L111-112, “Elemental compositions … aquation times.” It seems that your particle classification did not use all elements (e.g., Ti to Pb were not used). Should you remove them and renormalize the wt%?
- L260-262, “The C signals … S fraction values.” I understand that TEM uses a very high accelerating voltage, which enables electrons to easily penetrate the entire particles. However, it might still be beneficial to show the calculation of the penetration depth for pure metal or add a citation to make readers understand this concept.
Citation: https://doi.org/10.5194/egusphere-2025-2230-RC2 -
RC3: 'Comment on egusphere-2025-2230', Anonymous Referee #3, 15 Jun 2025
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This manuscript presented the elemental composition and mixing state of aerosol particles collected in the North Pacific at different altitudes. It is important to gain a better understanding of particle mixing state at the single-particle level, as this will affect radiative forcing and cloud formation. The manuscript found different impacts from different sources, including biomass burning, marine emission, and deserts during the field campaign. This study provides a valuable data set on the vertical profile of particle composition and mixing state. However, there are several issues that need to be addressed before it can be considered for publication.
General comments:
- Please revise the abstract to focus more on the main results of this investigation. The definition of different sampling periods in the abstract is unclear. The conclusions in Line 21-25 are too general and could apply to many similar studies.
- As the authors also mentioned, the method for particle classification is simplified (Line 120-132). Since you have the relative elemental composition of individual particles, is there a better classification scheme or clustering method that could distinguish particles with mixed components, which may help to provide a better description on the mixing state of particles.
- The discussion on the mixing state of the particle population and individual particles is not thorough, especially at the individual particle level. In both cases, the mixing state matrix mentioned by Riemer et al (2019) would provide more quantitative results to describe the mixing state.
- Justification and more discussion are needed on the method using Na/(Na+K) and S/(S+C) ratios to describe the mixing of sea salt and biomass burning aerosol, and sulfate and organics. Na-containing particles can also be emitted from biomass burning affect the ratio. Carbon in the EDS is semiquantitative. Secondary organic aerosol or materials would also contribute to the carbon in the particles. These should be considered.
Specific comments:
- Line 19, particle composition can’t be determined only by TEM but with EDS.
- Line 230-232, please elaborate on this statement.
- Line 329, organic coating may come from Secondary organic materials.
- Line 345, The dehydration RH for the K2SO4 is very high. Is there any RH data to support this?
Citation: https://doi.org/10.5194/egusphere-2025-2230-RC3
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