General comments:

Manuscript entitled “Origin of secondary fatty alcohols in atmospheric aerosols in a cool-temperate forest based on their mass size distributions” to investigate the origin and formation of secondary fatty alcohols (SFAs) based on their mass size distribution in aerosol samples obtained from a deciduous forest site. This manuscript gives us a clearer understanding of the five SFAs and their mass size distributions in the forest environment for the first time. The author concluded that the mass concentrations of SFAs were the highest in spring and the mass size distributions were highly correlated with bulk WIOC. Furthermore, SFAs were induced that mainly originated from plant wax from the results of the aerosol and leaf samples. This study provides new insights into possible source of primary biological aerosol particles (PBAPs) and their effects on the ice nucleation activity of aerosol based on seasonal changes in particles. Finally, these results demonstrated that the different growth stages of plants can result in differences in the size distributions of PBAPs. The Reviewer supports this manuscript for publication in Biogeosciences if the authors could carefully address the following comments.

Specific comments:

1. Why did the authors analyze only spring, summer, and autumn atmospheric samples, but not winter samples? In my opinion, the winter sample can be used as a blank comparative analysis, excluding the interference of other environmental factors. Please explain it in detail.
2. Page 2 Lines 32-33: Why is the particle size only analyzed to 10 μm? This is very confusing, 10 μm is represent the maximum particle size or larger than 10 μm? How is the particle size measured? If it is based on the sampler, you may be able to try more levels of impactors.
3. Humidity can influence the particle size distribution. Did the authors consider environmental factors (such as humidity) in the analysis.
4. Page 2 Line 34-36: For the analysis of SFAs, the authors choose the sampling time of 1 week and at a flow rate of 120 L min^-1, this indicating that the concentration of SFAs is lower. So please explain the atmospheric significance of analyzing SFAs and its seasonal variations.
5. Page 3 Lines 16-17: “a quarter of each sample filter with an aera of 10.18 cm2 was extracted using a mixture of dichloromethane and methanol (2:1, V:V)”. Why did the author choose the mixture of dichloromethane and methanol (2:1) as the extracted solution?
6. Page 7 Figure 3: Why is the error bar so large for the spring and summer samples in Figure 3?
7. Page 9 Figure 7: In the seasonal variation shown in Figure 7, the mass size distribution does not change significantly compared with Figure 11.
8. Page 12 Figure 10: It is suggested that the author place Figure 10 into the supplementary material.

This paper presents the atmospheric loadings and seasonal distributions of secondary fatty alcohols in size-resolved aerosols from a deciduous forest canopy at Hokkaido, Japan. The results obtained have been interpreted logically. Based on the distributions of n-nonacosan-10-ol and its non-linear relations with the primary organic aerosol markers in the same samples such as sucrose, trehalose, mannitol and arabitol in spring, summer and autumn together with the comparisons of the SFAs measured in plant leaves, authors have found that the SFAs are derived from plant waxes. Overall, the data presented here and the conclusions drawn from them are interesting and make a substantial contribution to the community of atmospheric- and biogeo-sciences. Therefore, I recommend this paper for final publication in BG, after addressing the following comments.

Specific comments:

Section 3.1 - Page 4, Lines 12-15: The average concentrations of SFA3 --- are smaller than those --- (Miyazaki et al., 2019). Here it is important to note the literature values and describe the potential reasons behind such lower levels (10~20 times) compared to those observed at Tomakomai experimental forest.

Section 3.3.1 – Page 8, Lines 13-14: Correlations between --- two seasons (Fig. 6a). It is contrary to a significant correlation (R2 = 0.70) reported between the n-nonacosan-10-ol and sucrose in forest aerosols by Miyazaki et al., 2019. So, I suggest the authors to compare the data (the sum of submicrometre and supermicrometre aerosol mass) with that (in TSP) reported by Miyazaki et al., 2019 in order to make it clear.