General comments: This manuscript discusses the influence of anthropogenic emissions on biogenic secondary organic aerosol formation in the upper boundary layer. The dataset includes samples collected at the mountain foot and mountain side of Mt. Hua China. They find that NOx impacts isoprene-derived BSOA formation at the mountain side and observe an inverse diurnal trend for isoprene-derived BSOA at the mountain foot and mountain side. Overall, the dataset is comprehensive and provides a valuable addition to the scientific community. I believe this manuscript is publishable after major revisions are conducted, as described below.

Specific comments:

• I would recommend that the authors review the more recent literature on isoprene-derived SOA formation. Specifically the articles Riva et al. 2019 (DOI: 10.1021/acs.est.9b01019) Lei et al. 2019 (https://doi.org/10.1021/acs.est.2c01579), Zhang et al. 2018 (DOI: 10.1021/acs.estlett.8b00044), and Cooke et al. (https://doi.org/10.1021/acs.est.3c10851). These experimental and modeling studies demonstrate that iSOA formation is more complex than what is described in the present article. For example, in lines 83 – 84 the authors that that sulfate would increase SOA formation. However, the previous articles demonstrate that this is not always true as core/shell morphology can form and limit further reactive uptake reactions and highly acidic sulfuric acid particles can limit the formation of organosulfates due to the poor nucleophilicity of bisulfate. I recommend the authors consider revising to include these details.
• Please include the pore size and manufacturer for the quartz filters used in collection.
• It would be beneficial for the reader if you could describe how you determined the mass concentration for the organic matter as well as for the individual species in the methods section. Did you have calibration standards for your species of interest?
• It would be helpful for the reader to include the Q values (Q true, Q robust, and their ratio) in section 2.4, particularly for others in the field who would like to conduct a similar PMF analysis of their data set.
• Throughout the manuscript, there is consistent error in presenting the uncertainties. For example in lines 199 : “30.0±10.4”. Uncertainties should only be provided to the last significant digit. Therefore, if your range is ±10, the technically correct way to present this would be “30±10”
• A citation is needed substantiating the claim that hopanes are a known tracer for combustion sources in lines 202-203
• In Figure 1, it is interesting to me that the mass concentrations of BSOA for I, M, and S, seem to be overall similar between MF and MS; yet, the percentages of sources are so different. Could the authors comment on this? I think a reader could have a similar curiosity.
• In lines 230 – 233 and 264-266, the authors may be interested to know that their MF mass concentration of iSOA products, and specifically 2-MTLs, is also similar to that recently measured in two regions of Mexico City (Cooke et al. 2024 https://doi.org/10.1021/acsestair.4c00048)
• A citation is needed in line 255 substantiating the claim that isoprene emissions are temperature-driven
• Lines 260 – 264, describe “CWT analysis.” Please define the acronym CWT for the reader and additionally provide details on this analysis in your methods section. As it is currently written, it is not clear to the reader what this refers to or how the data in this figure was generated.
• A citation is needed in line 290-293 for the studies that have discussed the formation mechanism of 2-MTLs and C5-alkene triols
• Have the authors found the presence of any BSOA(I) oxidation products? It would be interesting to see if there is a difference in these products at the MF vs. MS. See Armstrong et al. 2022 https://doi.org/10.1021/acs.est.2c03200 and more recently Yan et al. 2025 https://doi.org/10.1021/acs.jpca.4c08082
• Lines 367 – 368, it looks to me like only BSOA(I) correlates positively with ambient temperature and that BSOA(M) and BSOA(S) negatively correlate with temperature.
• Please provide references in line 379 – 382 substantiating the claim that ALWC, aerosol acidity, and gas-particle partitioning would influence BSOA formation
• Please provide reference is lines 391 – 392 substantiating the claim about high NOx/low NOx SOA pathways
• Lines 402 – 404, unclear to me how this shows that sulfate has a statistically significant relationship with BSOAI. Incorrect figure referenced? Not sure what this is meant to refer to.
• In this and the following sections, please see the above comment about more recent literature on the role of sulfate, morphology, and acidity in iSOA formation. The literature cited here is not up to date, and thus the interpretation of the measurements is not complete.
• Lines 417 – 418, again it is unclear to me how Figure 5c supports the claim in the text.
• Please reference Figure 6 properly in the text in paragraph starting in lines 417
• Line 439, please explain to the reader what is meant by “RF analysis”and include details on this in either the methods section or supporting information

Technical corrections:

• Line 108 “observations studies” to “observational studies”
• Line 115 “dramatical” to “dramatic”
• Lines 213-214 “believed to” to “believed to be”
• Lines 241 -242, should this say “more densely distributed”?
• In Figure 5, “pearson’s” has a red line underneath
• Lines 367, “Figure 6(a) to Figure 5a?
• Line 367, BOSA to BSOA
• Line 387 – Figure 6(a) to Figure 5a?

General comments:

This manuscript reports the field measurements of biogenic SOA tracers and anthropogenic emissions at two sampling sites in the Mount Hua region at different altitudes. Overall, while this study presents some interesting results, my primary concern is the lack of proper references in the discussion, which could impact the data interpretation. There are many typos and grammatical errors throughout the manuscript. I suggest the authors carefully correct these errors to improve the clarity of presented results. Below I have a few specific questions for the authors to consider.

Specific comments:

Lines 147-155: Please provide information regarding the extraction efficiencies for major BSOA tracers using the given analytical method.

Lines 155-161: Could the authors please verify the unit of “Ml” mentioned here? Do they mean milliliters (mL) or microliters (μL)?

Lines 207-210: “Nonetheless, an inverse diel pattern was observed at high elevation site with a daily OM peak at the moment (12:00~16:00) of strong photochemical activity, suggesting that OM components aloft was probably driven by photochemistry.” Does this statement refer to Figure S1(b)? Please specify.

Line 219: I would suggest changing “septuple” to “7-fold” here and using similar expressions throughout the manuscript if you intend to compare the fold changes. Similarly, I would suggest using “surface OM” and “OM aloft” throughout the manuscript if you intend to compare OM at different altitudes.

Line 260: Please define “CWT” for its first use in the main text.

Lines 278-280: “This finding was consistent with the laboratory measurements of 2-MGA being derived from oxidization of isoprene with high NOx load (Wang et al., 2008).” The “Wang et al., 2008” cited in the manuscript was not a laboratory study. Please provide correct references to support this statement.

Lines 289-293: “This was probably owing to that C5-alkene triols and 3-MeTHF-3,4-diols were mainly formed via acid-catalyzed intermolecular rearrangement reactions of epoxy-diols, whereas 2-MTLs are likely to the result from nucleophilic addition of water to the ring opening of epoxy-diols.” These statements require appropriate references. Regarding 2-MTLs, their formation has been linked to acid-catalyzed reactive uptake of isoprene epoxydiols. Recent field studies also suggest that 2-methyltetrols could be produced through biological processes within the plants and released into the atmosphere as primary emissions. Therefore, 2-MTLs can potentially originate from multiple sources (both primary and secondary) and via different mechanisms, all of which should be considered.

Lin, et al. "Isoprene epoxydiols as precursors to secondary organic aerosol formation: acid-catalyzed reactive uptake studies with authentic compounds." Environmental Science & Technology 46.1 (2012): 250-258.

Ye, et al. "Near-canopy horizontal concentration heterogeneity of semivolatile oxygenated organic compounds and implications for 2-methyltetrols primary emissions." Environmental Science: Atmospheres 1.1 (2021): 8-20.

Lines 330-332: “As a typical and abundant sesquiterpene, β-caryophyllene has been widely studied due to its high reactivity and significant aerosol formation potential; and it can be oxidated into β-caryophyllinic acid for via ozonolysis/photooxidation.” Please provide appropriate references to support this statement.

Line 347: typo on “Ox load”

Lines 364-365: Details for the mantel test and random forest analysis mentioned here should be included in the method section or the supplementary materials.

Line 370: typo on “rom”

Lines 376-377: Please specify the significance level.

Lines 384-385: “Evidences from field and modeling studies indicates that biogenic SOA yield is enhanced in presence of elevated NOx level (Xu et al., 2015; Shrivastava et al., 2017).” This statement is overly simplified and lacks sufficient detail regarding the role of NOx in biogenic SOA formation. The authors should more carefully discuss how NOx affect the fate of RO2 radicals in the presence and absence of NOx, and how the subsequent reaction products contribute to SOA formation and yields.

Lines 387 and 389: Figure 6(a) and Figure 6(b) here should be corrected with Figure 5(a) and Figure 5(b).

Lines 391-393: “As is well known, isoprene oxidization primarily follows two pathways, i.e., HO2 pathway forming 2-MTLs in NOx-limited conditions and NO/NO2 channel yielding 2-MGA in high-NOx scenarios.” Please provide appropriate references to support this statement.

Line 403: typo on “filed”