Conifer leaf wax acts as a source of secondary fatty alcohols in atmospheric aerosols

Cui, Yuhao; Tachibana, Eri; Miyazaki, Yuzo

doi:10.5194/egusphere-2025-4483

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https://doi.org/10.5194/egusphere-2025-4483

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22 Oct 2025

| 22 Oct 2025

Status: this preprint is open for discussion and under review for Biogeosciences (BG).

Conifer leaf wax acts as a source of secondary fatty alcohols in atmospheric aerosols

Yuhao Cui, Eri Tachibana, and Yuzo Miyazaki

Abstract. Fatty alcohols (FAs) are major components of plant leaf surface lipids emitted into the atmosphere as primary biological aerosol particles (PBAPs). FAs in the atmosphere can act as ice-nucleating particles to form clouds that affect climate through radiative forcing and precipitation processes. Secondary FAs (SFAs) in plant waxes can act as tracers for PBAPs. However, the specific plant species that contribute to the atmospheric emissions of SFAs, as well as the factors controlling the SFA amount of atmospheric SFA emissions, remain poorly understood. In this study, we collected size-segregated aerosols and leaf samples from various plant species from a cool-temperate forest site in Hokkaido, northern Japan, during different seasons. n-nonacosan-10-ol was the most abundant SFA in the aerosols, which resided mostly in the supermicrometer size range, with the maximum concentration observed in spring. Among all plant leaves examined, n-nonacosan-10-ol was identified only in coniferous leaf samples. The mass of n-nonacosan-10-ol per leaf exhibited a seasonal trend similar to that of the aerosol SFA concentrations. Our results suggested that the amount of n-nonacosan-10-ol in aerosols was primarily controlled by the number of n-nonacosan-10-ol coniferous trees, which was determined by the phenology. Overall, our findings suggest n-nonacosan-10-ol can be used as a tracer compound for PBAPs originating from conifer leaf wax, which can be used to estimate the atmospheric emission flux of PBAPs on a global scale.

Received: 12 Sep 2025 – Discussion started: 22 Oct 2025

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Yuhao Cui, Eri Tachibana, and Yuzo Miyazaki

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RC1:
'Comment on egusphere-2025-4483', Anonymous Referee #1, 22 Dec 2025 reply
Understanding the emission of PBAPs into the atmosphere and their impact is of high importance to the scientific community to deepen the understanding of the complex dynamics of our climate. This study focuses on the emission of secondary fatty acids as PBAPs tracers. The authors identified certain coniferous trees in Japanese forests and investigate SFAs from these trees by first directly assessing SFA concentration from the trees surface and compare these to SFAs in the atmosphere by sampling aerosol in proximity. Moreover, they set this into a seasonal perspective and compare it to a small number of meteorological variables.
The methodology is well thought out and the basis for good scientific work. The dataset is rather small but valuable, and makes the authors conclude with seasonal trends of SFA emission and that coniferous trees are the main emitter of SFAs. While the methodology provides a good basis for scientific quality, to this reviewer it was hard to follow the story. The results are presented step by step, however sometimes the reason why something is presented (or not) is inconclusive. The fact that winter is missing for most of the seasonal data is a bummer, also the fact that for summer there is only one datapoint. To me the question arises how to conclude with seasonal trends if only two seasons are supported with somewhat reliable data. Regardless of the reason for the missing data, the manuscript must acknowledge this limitation in the abstract and conclusion, and refrain from generalizing to seasonal trends, when it is rather a spring-autumn comparison.
Still, this manuscript provides interesting data worth publishing, but I suggest a major revision of the storyline and the data presentation, which will be described below.

Major points:
Seasonal trends: With field measurements it can be hard to get data for all seasons, however it is not well described why there is only one week of data in the summer and no data in the winter for the aerosol data. For leaves, Figure 7 presents winter data from a different species (Sakhalin spruce) than the other seasons (Sakhalin fir). This inconsistency makes the comparison invalid, otherwise clearly state why it is valid.

The manuscript could be reframed as a comparative study of Spring vs. Autumn. The Abstract and Conclusion must be revised to remove broad generalizations about "seasonal variations" where data is insufficient. I strongly suggest removing the winter data point from Figure 7.
Discrepancy Between Aerosol and Leaf Trends:
Aerosols (Figure 4): Spring concentrations are vastly higher than Autumn. Summer and Autumn are effectively indistinguishable given the large error bars in Autumn and the lack of variance data for Summer.

Leafs (Figure 7): Spring and Autumn masses are nearly identical (the authors even state the difference is "insignificant").

You state the trends in conifer leafs are similar as in the aerosol samples in your conclusion. Considering the previous comment the trends are not “similar”, rather contradicting. This needs to be addressed.

SFA as PBAP tracer: A central argument of the paper is that SFAs can serve as tracers for bulk water-insoluble organic carbon (WIOC). However, the evidence for this is relegated to Figure S2 in the Supplement. Since this relationship is foundational to the paper's significance, this figure should be moved to the main manuscript.

Minor points:
Introduction: The link between SFAs and ice nucleation is presented somewhat tenuously. The cited study (Qiu et al.) is simulation-based. I suggest citing experimental studies to strengthen this motivation (e.g. https://pubs.rsc.org/en/content/articlehtml/2024/ea/d4ea00066h).

Section 2.1 (Sampling Gaps): Please provide a brief explanation for the lack of winter aerosol data and the limited summer sampling. While logistical challenges are common, transparency is required.

Section 2.3 (Filter Analysis): Why do the filter cut areas differ between the bottom stage and upper stages? Furthermore, impactors often deposit particles non-uniformly (center-line concentration). Please clarify how the cuts were taken to ensure they were representative of the total loading.

Section 2.5 (Sample Processing Bias): The manuscript states that broadleaf samples were ground/homogenized, while coniferous needles were not. Please elaborate on this decision.

Section 3.2 / Table 1 (Detection Limits): "Not Detected" (ND) is used for broadleaves. Please state the Limit of Detection (LOD) for the analytical method.

Figure 10 (Meteorology): The correlation between wind speed and aerosol concentration in Spring appears weak visually. The authors should provide a scatter plot or statistical correlation coefficient to substantiate the claim that wind drives emissions. The inverse relationship in Autumn further complicates this hypothesis.

Sugar Compounds: The methodology mentions measuring sugar compounds, but these results do not appear to be discussed. Please either remove the mention or include the data.

Technical points:
Figure 1: A photo of the sampling site/equipment would be helpful for context.

Figure 3: The legend is disproportionately large; please resize.

Line 90: "temperature humidity" should be "temperature and humidity."

Line 95: The sentence "Consequently, the present study emphasizes..." lacks context. Please clarify that this refers to the data availability of Spring and Autumn.

Line 213-214: The claim of a peak in the 1.5–3.0 µm range is not well supported due to the large error bars; the peak definition is ambiguous in this range.

Line 290: Please define the specific months considered "growing seasons" for these specific tree species.

Lines 315-327: The detailed description of biosynthesis pathways seems tangential to the study's focus on emission fluxes. Consider shortening this section.

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Citation: https://doi.org/10.5194/egusphere-2025-4483-RC1
RC2:
'Comment on egusphere-2025-4483', Anonymous Referee #2, 22 Dec 2025 reply
General Comments
This manuscript, which builds on a previous study by Cui et al. (2023), examines the origin and emission of secondary fatty alcohols (SFAs) in size-segregated atmospheric aerosols collected at a cool-temperate forest site in Hokkaido, Japan. The authors identified n-nonacosan-10-ol as the predominant SFA produced by coniferous trees and compared the concentrations in conifer leaves to levels in aerosol samples collected across seasons. The authors observed a seasonal variability, but due to extremely limited sampling in the summer and winter, it may be more accurate to consider their findings a comparison of spring and autumn n-nonacosan-10-ol levels. However, the methods are comprehensive, and overall, the study provides interesting new insights into a biogenic source of atmospheric aerosols, despite a somewhat small dataset. Therefore, I support the publication of this manuscript in BG, after addressing the following comments.
Specific Comments
Fig 7/Table S4: The mass of n-nonacosan-10-ol shown for winter in Fig. 7 does not match the data presented in Table S4. According to Fig. 7, the mass of n-nonacosan-10-ol per leaf in winter is 2.32±34 mg, but the average mass of the winter values shown in Table S4 can be calculated as 16.17 mg. In addition, the winter n-nonacosan-10-ol masses are exactly the same as those for summer (16.9, 14.3, and 17.3 mg), and two of the three leaf weights shown for summer and winter are identical (4.51 and 4.58 mg). Please double check the data shown in Table S4 and confirm that the values align with what is shown in Fig. 7.

Table S3: Does ‘deep yellow’ refer to the brown part of the leaf? I might have missed it, but it seems that this specific color is not defined in the text.

Technical Corrections
Line 104 is missing the word the (‘These species were selected because they dominate the study site in the forest’).

Table S1 should be referenced in the main text.

Table S2 should be referenced in the caption of Fig. 6 or in nearby text.

A reference to Table S3 should be included in the main text.

Line 457 and 457: The supplement is referred to as Supplementary Material and Supplementary Information, respectively. Please select one for consistency.

Lines 476 – 479 need references.

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Citation: https://doi.org/10.5194/egusphere-2025-4483-RC2

Yuhao Cui, Eri Tachibana, and Yuzo Miyazaki

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Yuhao Cui, Eri Tachibana, and Yuzo Miyazaki

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Short summary

We investigated the specific plant species that act as a source of secondary fatty alcohols (SFAs) in atmospheric aerosols and their emission processes. Our study at a cool-temperate forest site suggested that SFAs in aerosols originated from conifer leaf wax and their atmospheric emission amount is primarily controlled by conifer abundance and the phenology of leaves. Our findings provide insight into estimating the global atmospheric emission flux of primary biological aerosol particles.


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