In the study titled 'Impact Assessment of Terrestrial and Marine Air Mass on the Constituents and Intermixing of Bioaerosols over Coastal Atmosphere,' the authors aim to explore the effects of sea-land air mass exchange on the spatial and temporal distribution of aerosols, as well as potential intermixing processes in coastal regions.

In my opinion, the study demonstrates considerable potential: it integrates current molecular biology methods applied to atmospheric aerosol sampling at low altitude (15 meters above the ground) with concepts of atmospheric physics to understand the effects of mixing at the land-ocean interface on the ion and trace metal composition of air masses and their associated microbial composition (bacteria and fungi). The study is comprehensive, relying on current methods for both sample processing and statistical analysis. The results are interesting, original, and relevant to a field that remains under-researched.

However, I find the paper long and often overly descriptive. The message is not always clear, particularly regarding the microbial communities section, with some inaccuracies present. Some parts are also too speculative, in my opinion, and not sufficiently connected to the current literature. Overall, I believe the results and discussion sections need thorough revision

That said, I believe this article deserves to be published in EGUsphere, provided certain major changes are made.

General comments:

Field blanks are missing, raising the question of how to evaluate the effect of cross-contamination between air masses. This issue is crucial and must be addressed, as air samples are highly susceptible to contamination due to their low microbial biomass.

I am also skeptical about the calculation of 24-hour back trajectories. I believe there is a considerable loss of information that may affect the interpretation of the data. The region in question is influenced by multiple geographical conditions. Extending the backward trajectories could provide better insights into the patterns of microbial assemblages in the observed air masses, especially in the context of long-distance transport

How can the local contribution to pollution be determined? The authors state that 60% of their air masses have a terrestrial origin, yet only three episodes of severe pollution were observed. How can they be certain that this pollution originates from distant sources?

Specific Comments:

Title: The word “impact” implies an environmental impact study or risk assessment, which is not the case. I suggest modifying it slightly to better reflect the characterization aspect.

L125-127 and 163-164: How do the authors link air masses at an altitude of 500 meters with their sampling site at 15 meters?

L129 – 131: The authors specified the use of PM2.5 samplers equipped with 47 mm quartz filters but did not provide specific details about the type of PM2.5 sampler used, such as the flow rate and manufacturer information. Please specify.

Additionally, did the authors use field blanks as controls? Was the device cleaned between quartz filter changes? If so, please specify the cleaning procedure. Furthermore, was the air flow rate calibrated before and after sampling to ensure accurate measurements?

L144-145: “The membranes were meticulously weighed using a Mettler XP-6 balance with an accuracy of 10-6 g. Prior to weighing, the membranes were maintained in a controlled environment with consistent temperature and humidity for a duration of 24 hours.”

I assume this step aims to remove water from the filters. How did the authors ensure that all residual water was removed, given that residual moisture can significantly affect the filters' weight? Additionally, did the authors sample during rainfall events? Is the sampler equipped with a rain cap? Were the filters exposed to rain, and if so, how were they processed?

L149-155: The protocol for the characterization of ions and metallic elements lacks details. Please specify the sonication time, the type of column used, and the reference for the conductivity detector.

L163-168: The authors defined their criteria for classifying air masses as continental or marine but did not explicitly mention the method they used to determine the origins of air masses. Please elaborate on the method used to categorize the air masses as marine or terrestrial.

L170-171: The authors state that they extracted DNA directly from the quartz filters. Did they use the same filters that were used for the previous ion and metallic element determinations? Additionally, was the DNA extracted from the entire filter or just a part of it?

172-173: The extracted DNA was measured using a Nanodrop spectrophotometer (Nanodrop 2000, Thermo Scientific USA) to determine the concentration. I am surprised that the authors were able to quantify the DNA in their samples using a Nanodrop, considering its sensitivity is around 2 ng/µl. Could the authors provide more details about the measured DNA concentrations to clarify?

L234-238: The phrasing of this sentence is confusing. It appears to mix the concepts of Mantel correlation analysis and Spearman's rank correlation coefficient. Could the authors clarify if the Mantel test was conducted using Spearman's rank correlation coefficient as the measure of correlation, or if separate Spearman's rank correlation analyses were performed? A clear explanation of the statistical methods used would be helpful.

275 :277: “The introduction of marine air mass from the west led to the elimination of the pollution, resulting in an average PM2.5 concentration reduction to 7.92 μg /m3.”

I understand that dilution could be a factor, but stating that there was an elimination of pollution seems uncertain. Did the air masses in the following days also have a terrestrial origin? Please elaborate.

L290-293: “The concentrations of NO3-, SO42-, and NH4+ were significantly influenced by both terrestrial and mixed air masses, with the latter exhibiting a more pronounced effect (NO3-, 10.65±3.26 μg/m3; NH4+,7.39±3.30 μg/m3; SO42- 6.76±1.77 μg/m3)”

I do not see any statistical test mentioned, and the standard errors (if they are standard errors, as this is not specified in the legend) seem large. Furthermore, there are no standard errors reported for the trace metal elements. Why is this? Please revise.

L327-328: Unless I am mistaken, the authors did not measure the bacterial and fungal concentrations directly but estimated their concentrations based on the quantity of 16S rRNA genes, which is not exactly the same. Additionally, do these concentrations apply to all air masses combined? Please revise.

L332-333: “The terrestrial air masses came from the inland areas, which carried more microorganisms from anthropogenic activities and natural sources with high resistance to high temperatures, dryness, and strong ultraviolet rays (Gong et al., 2020)"

The current phrasing of this sentence is odd. The paragraph that discusses the different genera and their resistance to temperature, dryness, and UV radiation appears later (L348). As it stands, this sentence seems more speculative.

L333-335:  Please specify the statistical test used and the associated p-value in the text.

353-358: The authors claim that the higher abundance of cyanobacteria originates from soils. However, to my knowledge, cyanobacteria are mostly found in aquatic environments, although their presence in soils has been reported many times. Could this not indicate that the air masses had significant contact with marine surfaces? Additionally, why were the backward trajectories calculated over 24 hours and not 72 hours or more? A longer period would provide a better understanding of how the air masses are influenced by various surfaces.

L327-376: “Streptococcus are mostly found in the oral and gastrointestinal tracts of a variety of mammals and have not been shown to play a role in human infections to date (James et al., 2015). Ruminococcus, and unclassified Enterobacteriaceae are gut microorganisms that may be related to the marine fish and other animal gut microbes.”

The sentence is not correct. Streptococcus plays a significant role in human infections. Additionally, Enterobacteriaceae are also found in the human microbiome. Please rectify.

L394-396: “In contrast, Comamonas was identified as an indicator bacterium in marine air- mass samples, which is dominant in coastal cities (Wei et al., 2020) and originates from soil, activated sludge, and water (Yan et al., 2012).”

I am unsure how to interpret this sentence. The authors identified Comamonas as a marker of marine air mass, but they immediately suggest a soil/anthropogenic origin. How can this be a good indicator of marine air masses?

L454-457: “Dust-borne bacteria (Staphylococcus, Delftia, Pseudoalteromonas and Deinococcus) were injected into the atmosphere during dust events, and most of them accompanied the dust transportation to the downwind of Asian Dust including the coastal city of Weihai.”

Do the authors have any additional data to support such a statement? Specifically, can you provide PM10 concentration data to confirm the occurrence of these dust events?

L459-462: “Similarly, microbial communities showed high positively correlated with ions from continental sources, such as K+, Mg2+, and Ca2+, which indicated that microorganisms carried by mixed air masses were mostly from continental sources”

The authors claim that microorganisms originate from land because of these correlations. However, they also argue in L298–300 that Mg²⁺ is a typical component of sea salt. While I do not necessarily disagree with their observation, I find it difficult to make such a definitive statement based on their dataset. Did the authors consider performing a simple correlation between the air mass origins and the concentrations of microorganisms?

L462-463: What does a negative correlation with wind direction mean, and how should it be interpreted? I am not sure I understand. Please elaborate.

L464 – 465: “Wind blowing from continent or marine may play important role in microbial community diversity (Jones and Harrison, 2004)”

I am not certain that the wind measured at 15 m above ground level at the sampling station is representative of the entire air mass, but rather reflects a significant local effect. Could the wind have affected the sampling efficiency? How should this effect be interpreted?

L468-469: “The marine air masses are generally clean and have a strong scavenging effect on air pollutants."

I disagree, especially in the context of the study where marine air masses are likely transported over nearby lands if integrated over longer periods. The presence of genera such as Streptococcus, Enterobacteriaceae, and Staphylococcus indicates a probable human influence. However, it remains difficult to determine whether this influence is local or if the observed genera are the result of long-distance transport. Additionally, I do not understand this scavenging effect mentioned. At best, there could be a dilution effect, but why would an oceanic air mass remove pollutant? Please rephrase or clarify.

L474-475: Unless I am mistaken, the temperature was only measured at the sampling site and is not representative of the conditions encountered during transport. Could this relationship indicate a significant site effect?

501-502: “Conversely, the marine air mass facilitates the removal of pollution, introducing a higher number of saprophytic microorganisms”

I am not sure what the authors are suggesting here. Are they implying that airborne microorganisms can remove pollution? Please elaborate. This seems unlikely to me, as several studies show that the contribution of microorganisms to atmospheric chemical processes is very minor compared to physical processes.

Additional minor comments:

L39: Please change the too generic word “crucial” or elaborate on why bioaerosols are so crucial.

L124-127: It would be valuable to provide the altitude above sea level as well.

L245: “The terrestrial air mass accounted for 59.94%” of what? Total air masses reaching the sampling site? Please clarify.

L448: There is a typo, “concertation was” should read “concentration were”

L471: There is a typo. The sentence should read “which suggests an obvious influence from marine sources.”

L523: There is a typo, a “s” missing to “Staphylococcu”

Figure 1: Why is there two separate stacked histograms for each event? What does the legend of the graph represent? I’m guessing the altitude, but then why is it negative (-274) ?

Figure 2: The legend should clearly specify the criteria used for selecting the main genera.

Figure 3: Would it possible to display clearly the number of each air masses (n) computed in the statistical analyze? What about the error bars?

Figure 4: A P value of 0.0522 was displayed on Figure a. Since it’s above the above the significant threshold of 0.05 set up in the statistical part, I suggest to use a different nomenclature if the authors still want to point out that the difference is nearly significant. Especially considering that test can’t tell which of the air masses are different from the other. Also what about the error bars and number of individuals (n)?

Figure 5: The legend shows a Pearson r coefficient, but it is stated in the statistical analysis section that Mantel tests were computed using Spearman's rank correlation. Please rectify. Also, please clarify what “Cells” refer to, I didn’t find it anywhere in the manuscript.

The manuscript submitted by He et al. has a considerable and original work to clarify the interactions between bioaerosols, airborne chemicals and their sources. Although I would consider it eligible to publish, some major explanations and analyses are needed, with special attention to writing and organization of the manuscript, and some disagreement that should be discussed or clarified.

Major changes

- Introduction section. Lines 83-116 provides very specific and detailed information, which corresponds (and can be used) for a formal discussion section. I suggest to shorten this part, keeping the main ideas to justify the work and set up the objectives but with less details of previous works.

- Materials and Methods. A representative reference for chemical elements analyses would be appreciated, since no much details are provided. FAPROTAX and FUNGuild references should be specified.

- Results and Discussion.

I think the manuscript would benefit from an appropriate Discussion section, separated from Results. Comments from some results are too long and descriptive to follow the results fluently, and also some marks are repetitive, as Deinococcus (lines 348 and 388), Comamonas (lines 367 and 394). I would suggest split Results from Discussion, making the former shorter and focused on the data, and use the information to elaborate a discussion properly, without duplicities and allowing you to explain the relationships and hypotheses in a more consistent fashion.

The title “3.1 Air mass backward trajectory” does not correspond properly with the content described in this section.

Several times, “spring season” (L262, L309, L474, L491, L536) is cited in the manuscript, but the sampling was conducted mostly in winter days. It is confusing. These references are based on other works? Did one of the Pollution episodes occur in Spring? Explain it.

Fig. 1. Please indicate the date of the events and the different scale for left and right axes.

NMDS or PCoA, and their respective ANOSIM or PERMANOVA analyses would increase the support some conclusions.

Fig. 2. I am guessing that left axis of the graphs are not on 100% but 1%.  How the authors explain the substantial change in fungal communities? For instance, Aspergillus completely disappeared from the top abundance in MIX when it was the top one for TE and MA.

Lines 425-428 are hard to interpretate. Please revise. Are they a conclusion or supported information to your results?

Section 3.4 Community disparities influenced by terrestrial, marine and mixed air masses. The disparities mentioned in L387-388 are not supported statistically according to Fig. 3 or the p-values numbers are wrong. The same goes for the fungal graphs and text, for which the p-values do not concord (Aspergillus, p=0.014 or p=0.1498 ?; Malassezia, p=0.041 or 0.047??).

Fig. 5 shows correlations with “Bacteria”, “Fungi”, and “Cells”. Firstly, the legend shows “Pearson’s r”, when in Materials and Methods is specified Spearman’s. Please clarify this point. Bacteria and Fungi correlations with chemical elements are referred to concentrations or community compositions? “Cells” are the direct sum of bacterial and fungal concentrations?

PM2,5 and PM10 concentrations were positive correlated. However, the authors found a negative correlation with PM10 concentrations but not with PM2,5. Moreover, several studies have shown a positive correlation between richness and microbial concentrations with PMs concentrations. The authors should elaborate a discussion about this. Are the correlations maintained by group of microorganisms (bacteria or fungi) or this is only observed when the addition of both is conducted?

RDA analysis with the environmental and physicochemical parameters would be complementary to correlations.

L469: “The marine air masses are generally clean and have a strong scavenging effect on air pollutants”. From Fig 5., Wind speed is positively correlated with PMs concentrations in marine air masses (higher speed  higher concentrations) and negatively with Continental ones. How does it fit with the clearance effect the authors propose?

Lines 480-509 reminds a mixture of Discussion and Conclusions. This would be solved by separating Results and Discussion.

Minor changes

Typos:

L324: a point (.) before reference.

L342 Actionbacteria--> Actinobacteria

L448 Concertation--> Concentration