From the journal Environmental Science: Atmospheres Peer review history

24-Sep-2023

Dear Dr Rudich:

Manuscript ID: EA-ART-07-2023-000104
TITLE: Atmospheric Aging Modifies the Redox Potential and Toxicity of Humic-like Substances (HULIS) from Biomass Burning

Thank you for your submission to Environmental Science: Atmospheres, published by the Royal Society of Chemistry. I sent your manuscript to reviewers and I have now received their reports which are copied below.

After careful evaluation of your manuscript and the reviewers’ reports, I will be pleased to accept your manuscript for publication after revisions.

Please revise your manuscript to fully address the reviewers’ comments. When you submit your revised manuscript please include a point by point response to the reviewers’ comments and highlight the changes you have made. Full details of the files you need to submit are listed at the end of this email.

Please submit your revised manuscript as soon as possible using this link :

*** PLEASE NOTE: This is a two-step process. After clicking on the link, you will be directed to a webpage to confirm. ***

https://mc.manuscriptcentral.com/esatmos?link_removed

(This link goes straight to your account, without the need to log in to the system. For your account security you should not share this link with others.)

Alternatively, you can login to your account (https://mc.manuscriptcentral.com/esatmos) where you will need your case-sensitive USER ID and password.

You should submit your revised manuscript as soon as possible; please note you will receive a series of automatic reminders. If your revisions will take a significant length of time, please contact me. If I do not hear from you, I may withdraw your manuscript from consideration and you will have to resubmit. Any resubmission will receive a new submission date.

The Royal Society of Chemistry requires all submitting authors to provide their ORCID iD when they submit a revised manuscript. This is quick and easy to do as part of the revised manuscript submission process. We will publish this information with the article, and you may choose to have your ORCID record updated automatically with details of the publication.

Please also encourage your co-authors to sign up for their own ORCID account and associate it with their account on our manuscript submission system. For further information see: https://www.rsc.org/journals-books-databases/journal-authors-reviewers/processes-policies/#attribution-id

Environmental Science: Atmospheres strongly encourages authors of research articles to include an ‘Author contributions’ section in their manuscript, for publication in the final article. This should appear immediately above the ‘Conflict of interest’ and ‘Acknowledgement’ sections. I strongly recommend you use CRediT (the Contributor Roles Taxonomy, https://credit.niso.org/) for standardised contribution descriptions. All authors should have agreed to their individual contributions ahead of submission and these should accurately reflect contributions to the work. Please refer to our general author guidelines https://www.rsc.org/journals-books-databases/author-and-reviewer-hub/authors-information/responsibilities/ for more information.

I look forward to receiving your revised manuscript.

Yours sincerely,
Dr Lin Wang
Associate Editor, Environmental Science: Atmospheres

Environmental Science: Atmospheres is accompanied by companion journals Environmental Science: Nano, Environmental Science: Processes and Impacts, and Environmental Science: Water Research; publishing high-impact work across all aspects of environmental science and engineering. Find out more at: http://rsc.li/envsci

************

Reviewer 1

In this new submission, Li et al interrogates us about the health impact modifications induced by night time ageing of biomass particles by O3 and NO3 chemistry. They found that atmospheric transformations through O3 or NO3 reactions at nighttime modify the redox potential and cytotoxicity of HULIS aerosols. Their findings show a significant impact of multiphase chemistry on the overall health effects of organic aerosols.
This manuscript is well written and certainly falls within the scope of the journal. I would recommend its publication subject to minor changes.
The ozone coefficient reported in table S1 are quite high (ca 1e-4), especially for the high concentrations used during this study (> ppm). Is this the consequence of the protocol used to collect, extract and finally concentrate reactive component of wood smoldering emissions? Would this affect the conclusions made here and especially their extrapolation to atmospheric conditions?
What follows aims at triggering some discussion. The increase of the ozone uptake rates as a function of relative humidity has been reported already, and leads to :” Ozonolysis under higher humidity significantly reduced HULIS OP and AOC, indicating that higher RH promoted the decomposition or deactivation of the redox-active components within HULIS.” Could you get more precise? At higher humidity (and probably at high pH with the particles), O3 itself could act as an electron scavenger (by trapping labile electrons out of various quinones type functionalities for instance). Then, the O3 uptake rate would also be a measure of the OP of aerosols but also a metric of the reduction of particle’s OP during atmospheric ageing. Any thoughts on this?
There is no mention of the impact of N2O5 chemistry during the NO3 ageing experiments. N2O5 is a good nitrating agent under mild conditions, and its impact certainly underestimated here at high RH. The manuscript would benefit from some additions about the potential role of N2O5, which will efficient on reactive organics (as those selected here, see my previous points above).
It would be important to stress that the effective second-order kinetics for the depletion of redox-active moieties in HULIS do correspond to multiphase processes and are therefore depend of the type of droplet considered, and cannot therefore simply be extrapolated to other conditions.

Reviewer 2

The manuscript presented delves into the study of the oxidative potential (OP) and total antioxidant capacity of HULIS aerosols. It further characterizes the redox potential and cytotoxicity of nighttime atmospheric aging HULIS, explores the kinetics and lifetime of HULIS redox-active moieties with O3 and NO3• reactions, and examines how redox potential and ROS generation by HULIS evolve in lung fluid mimics. Key findings include the alteration of the redox potential and cytotoxicity of HULIS aerosols due to nighttime atmospheric transformations via O3 or NO3•. These atmospheric chemical changes are crucial in determining the redox reactions and toxicity of HULIS aerosol within lung fluid. The results emphasize the evolving health impacts of HULIS, underscoring the significance of addressing both atmospheric and respiratory system chemistry when evaluating the health implications of organic aerosols. While the manuscript is generally well-structured, several areas require further clarification or context before approval.

Major comments:
1. The later part of the paragraph delves deep into nighttime atmospheric chemistry, specifically O3 and NO3• reactions. Some context or background on why this is significant would help guide the reader.
2. Is the choice of wood smoldering emissions based on their predominance in certain environments or their particular chemical nature?
3. The study uses high oxidant exposures to simulate long-term transport in the atmosphere (line 97). How does this high exposure compare to actual real-world conditions, and how do you ensure it doesn't introduce artifacts in the aging process?
4. Is the use of three scenarios for nighttime aging (line 89) comprehensive or are there other potential scenarios that were not considered?
5. The study design was not demonstrated clearly, for example, how many samples were implemented? In terms of the cell experiment, how many duplicates were finished?
6. Could you elucidate how the lung fluid mimics employed in this study accurately represent real-life scenarios?
7. Why was the 4-hour timeframe chosen for the study of HULIS in neutral lung fluid?
8. It would be beneficial to further explain the implications of the findings and the significance of the observed effects on the antioxidant capacity and redox potential of HULIS aerosols.
9. For the lay reader, a brief explanation about what OP and AOC are and their significance would be helpful. What is the significance of H2O2eq? An introductory sentence might help.
10. For clarity, provide a brief explanation or definition about what redox proxies are and their relevance.

Dear Editor,

Enclosed, please find our detailed replies to the reviewers’ comments. We thank you and the reviewers for providing important and helpful comments.
Best regards
Yinon Rudich on behalf of all coauthors.
Referee: 1
Comments to the Author
In this new submission, Li et al. interrogates us about the health impact modifications induced by night time ageing of biomass particles by O3 and NO3• chemistry. They found that atmospheric transformations through O3 or NO3• reactions at nighttime modify the redox potential and cytotoxicity of HULIS aerosols. Their findings show a significant impact of multiphase chemistry on the overall health effects of organic aerosols. This manuscript is well written and certainly falls within the scope of the journal. I would recommend its publication subject to minor changes.
Answer: We appreciate the reviewer’s comments on the manuscript!
1. The ozone coefficient reported in table S1 are quite high (ca 1e-4), especially for the high concentrations used during this study (> ppm). Is this the consequence of the protocol used to collect, extract and finally concentrate reactive component of wood smoldering emissions? Would this affect the conclusions made here and especially their extrapolation to atmospheric conditions?
Answer: The effective surface uptake coefficients of O3 by HULIS particles were estimated in the range of (0.6-1.8)×10-4 as functions of RH and initial O3 concentration. The coefficients were estimated from the wall loss corrected O3 sink (measured in the flow tube without HULIS aerosols) to HULIS particles by ignoring gaseous reactions in the flow reactor system. These effective uptake coefficients were the result of multiple physical and chemical processes involving O3 and HULIS. It has been reported that the organic surface uptake of O3 is determined by particle surface property (size, morphology, chemical nature, viscosity, etc.) and environmental parameters (temperature, RH, pressure, light irradiation, etc.). The uptake coefficients can vary from mulch lower values of 10-6 for PAHs-coated particles to roughly 10-3 on pure alkene aerosol particles, such as oleic acid (Evaluation 19, May 2020; https://jpldataeval.jpl.nasa.gov/download.html).
Actually, the effective uptake coefficients of O3 derived in this study are comparable with many documented values for both laboratory and field organic aerosols, including biomass smoldering relevant pollutants (Baduel et al., 2011; Knopf et al., 2011; Konovalov et al., 2012; Li et al., 2019; Nash et al., 2006; Rudich et al., 2007). Thus, we believe the effective uptake coefficients of O3 used in the study are reasonable, and the extrapolated results of HULIS aging via O3 and NO3• are realistic and of environmental significance.
2. What follows aims at triggering some discussion. The increase of the ozone uptake rates as a function of relative humidity has been reported already, and leads to:“Ozonolysis under higher humidity significantly reduced HULIS OP and AOC, indicating that higher RH promoted the decomposition or deactivation of the redox-active components within HULIS.” Could you get more precise? At higher humidity (and probably at high pH with the particles), O3 itself could act as an electron scavenger (by trapping labile electrons out of various quinones type functionalities for instance). Then, the O3 uptake rate would also be a measure of the OP of aerosols but also a metric of the reduction of particle’s OP during atmospheric ageing. Any thoughts on this?
Answer: The sentence has been revised as “Ozonolysis under elevated humidity levels (≥ 30% RH) decreased HULIS OP and AOC, suggesting that increased RH enhances O3 oxidation in parallel to the decomposition or deactivation of the redox-active components (RACs) within HULIS.” (Line 222-225)
The relationship between O3 uptake rate and particles’ OP is quite an enlightening viewpoint. It should be noted that organic particles’ OP is measured in acellular solution with an antioxidant proxy (such as DTT and ascorbic acid, AA) arise from the intrinsic oxidizing compositions within particles, including organoperoxides, quinones, and electron-deficient alkenes. The formation or decomposition of these oxidizing compounds through O3 oxidation is determined by organic precursors and by the degree of O3 oxidation. For example, O3 reaction with PAHs can initially generate ozonides, hydroxy-PAHs, and quinones that have higher AOC and OP than the precursors. At the same time, further O3 oxidation may induce more ring cleavage to produce low molecular organic acids, leading to a decrease in OP and AOC. This suggests that simple ozone uptake as a physical process can hardly reflect the intricate chemical changes within the particles, nor the redox potential changes of particles. However, the idea that O3 traps out labile electrons from various quinoid functions to decrease particles’ OP can also be described as O3 electrophilic attack to break the functional groups of quinones and phenols. Overall, the idea is interesting and deserves deep thinking in our upcoming study.
3. There is no mention of the impact of N2O5 chemistry during the NO3• ageing experiments. N2O5 is a good nitrating agent under mild conditions, and its impact certainly underestimated here at high RH. The manuscript would benefit from some additions about the potential role of N2O5, which will efficient on reactive organics (as those selected here, see my previous points above).
Answer: We thank the reviewer’s constructive suggestion. Surface uptake of N2O5 is largely influenced by RH (Bertram and Thornton, 2009; Thornton et al., 2003), and the dry environment (RH<1.5%) in the NO3• aging experiments inhibits N2O5 uptake by HULIS aerosols. From our box model analysis (Text S1 and Figure S3), at low NOx scenario, the NO3• uptake by HULIS aerosols was two orders of magnitude higher than N2O5 uptake. It was 1.5 folds of N2O5 uptake at a high NOx scenario, implicating the potential importance of N2O5 chemistry in transforming HULIS only at a high NOx scenario. However, the exact pathways and mechanisms of N2O5 sink were not clear. Studies reported several reaction pathways explaining the sink of organic substance uptaken N2O5, including N2O5 decomposition into NO2 and NO3•, hydrolysis of N2O5 into HNO3, and redox reaction with organics to HNO3 and NO, of which thermo-decomposition and heterogeneous hydrolysis of N2O5 are considered as main channels (Escorcia et al., 2010; Galib and Limmer, 2021; Jahl et al., 2021; Mozurkewich and Calvert, 1988; Saathoff et al., 2001; Wen et al., 2022).
Monitoring the real NO3• and N2O5 concentration was not available, and distinguishing N2O5 chemistry from NO3• reaction is beyond our ability and also out of the current scope, which investigated the redox potential and toxicity changes of HULIS aerosol in the air and lung liquid. We will take this suggestion in our next study and optimize the experimental procedure in the application of crystal N2O5 as NO3• source, which shall be better for understanding the roles of N2O5 as NO3• in transforming organic aerosols.
4. It would be important to stress that the effective second-order kinetics for the depletion of redox-active moieties in HULIS do correspond to multiphase processes and are therefore depend of the type of droplet considered, and cannot therefore simply be extrapolated to other conditions.
Answer: Absolutely right! We acknowledged the limitations of the current study and highlighted the complexity of atmospheric transformation in aerosols’ redox potential and toxicity (Line 353-362). The constrain statement from the reviewer also inspires us to continue our studies.
 
Referee: 2
Comments to the Author
The manuscript presented delves into the study of the oxidative potential (OP) and total antioxidant capacity of HULIS aerosols. It further characterizes the redox potential and cytotoxicity of nighttime atmospheric aging HULIS, explores the kinetics and lifetime of HULIS redox-active moieties with O3 and NO3• reactions, and examines how redox potential and ROS generation by HULIS evolve in lung fluid mimics. Key findings include the alteration of the redox potential and cytotoxicity of HULIS aerosols due to nighttime atmospheric transformations via O3 or NO3•. These atmospheric chemical changes are crucial in determining the redox reactions and toxicity of HULIS aerosol within lung fluid. The results emphasize the evolving health impacts of HULIS, underscoring the significance of addressing both atmospheric and respiratory system chemistry when evaluating the health implications of organic aerosols. While the manuscript is generally well-structured, several areas require further clarification or context before approval.
Answer: We thank the reviewer’s comments.
Major comments:
1. The latter part of the paragraph delves deep into nighttime atmospheric chemistry, specifically O3 and NO3• reactions. Some context or background on why this is significant would help guide the reader.
Answer: Daytime OH• photooxidation and nighttime chemistry via O3 or/and NO3• reactions are the two important channels that modify atmospheric organic aerosol and their effects. We summarized the studies on the two aging pathways in the Introduction (Line 44-46, Line 55-72). We introduced the research gap, especially the much less studied nighttime O3/ NO3• oxidation in transforming the redox potential and toxicity of organic aerosols.
2. Is the choice of wood smoldering emissions based on their predominance in certain environments or their particular chemical nature?
Answer: Yes, we selected the wood smoldering emitted HULIS as a research object based on both its predominance in urban and rural PM2.5 pollution and its particular chemical nature of high redox activity, light absorbing, and potential toxicity.
Biomass smoldering burning, such as forest fires, agricultural field burning, and domestic biofuel heating, accounts for one of the most important sources of atmospheric and indoor organic aerosols in regional and global scales (Baker et al., 2016; Nema et al., 2012; Singh, 2022; Ward and Noonan, 2008). In general, organic aerosols emitted from smoldering burning can contribute to about 30 to more than 70 wt.% of PM2.5 at urban and rural sites, leading to significant radiative forcing and to millions of premature deaths and cardiovascular and respiratory diseases (Krall et al., 2013; Li et al., 2015; Martins and Da Graca, 2018; Southerland et al., 2022). HULIS contributes the major redox-active, light absorbing, and toxic fraction of the smoldering burning emitted organic aerosols (Li et al., 2022; Tan et al., 2016; Xu et al., 2020).
With global climate warming and drying, wildfires and peatland smoldering shall increase in frequency and scale. For instance, the routine and latest forest fires in California and Hawaii, Canada, Australia, and in the Indo-Gangetic Plain (IGP) in India have become national public safety events, threatening the health of people and the ecosystem (Abatzoglou et al., 2021; Alizadeh et al., 2021; Singh et al., 2018).
Given the escalating concern over smoldering organic aerosols and associated HULIS pollution, it's evident that our understanding of the characteristics, transformations, and health implications of HULIS in the atmosphere, particularly through atmospheric aging, remains limited. This underscores the significance of our current research, which seeks to elucidate the dynamic toxicity of HULIS as it travels through the atmosphere, ultimately offering insights to regulate better and manage HULIS pollution
3. The study uses high oxidant exposures to simulate long-term transport in the atmosphere (line 97). How does this high exposure compare to actual real-world conditions, and how do you ensure it doesn't introduce artifacts in the aging process?
Answer: This is an important question. First, the rapid high oxidant exposure simulating atmospheric aging of organic aerosols over long-term transportation is fundamental in laboratory investigation and a core principle of various flow reactor systems, including the widely used potential aerosol mass chamber and many other oxidative/aerosol flow reactors (PAM chamber/OFR/AFR), that offset the disadvantages of traditional aerosol chamber that has limited oxidant exposure and requires prohibitable long exposure times (Kang et al., 2007; Simonen et al., 2017). Second, numerous studies employing flow reactors have verified the similar chemical composition and physical properties of the formed aerosols compared to those formed in the atmosphere chemistry (Bruns et al., 2015; Hodshire et al., 2019; O’Brien et al., 2014). In the current study, we found consistent chemical and light absorption changes of aged HULIS with that reported for field biomass burning organic aerosols. Thus, we believe that the high oxidant exposures in the flow reactor provide promising and reliable results in directing the dynamic evolution of HULIS aerosols in redox potential and toxicity against O3 or NO3 reactions.
4. Is the use of three scenarios for nighttime aging (line 89) comprehensive or are there other potential scenarios that were not considered?
Answer: We have to admit that the actual atmospheric environments that transform organic aerosols are far more complicated than the conditions we explored in the study (Line 45-46). But the three scenarios represent the essential aging pathways that modify organic aerosols in the atmosphere. O3 and NO3• are the main oxidants in nighttime atmospheric chemistry, while the RH and anthropogenic pollutant of NOx are two of the key environmental parameters that mediate the atmospheric chemical processes under varying pollution levels. We aim to offer an initial holistic view of the dynamic toxic and chemical evolution of HULIS in the atmosphere and in the respiratory system.
We have added one note: “Moreover, atmospheric organic aerosols from diverse sources are more intricate than the HULIS, and there are more complex transformation processes beyond the simple nighttime simulations via O3 or NO3•, such as continuous diel agings of aerosols during their long-term transport. The three scenarios explored can hardly tell the lifetime behaviors of organic aerosols in the air, not even in the respiratory system.” (Line 355-358)
As stated in the current manuscript, the identified limitations call for further and wider research in this field to gain more comprehensive understanding of organic aerosols’ impacts during their lifetime transportation in the real troposphere.
5. The study design was not demonstrated clearly, for example, how many samples were implemented? In terms of the cell experiment, how many duplicates were finished?
Answer: We have added the information in the manuscript as below
Line 153: The results are expressed as the means ± standard deviation (SD) of at least two experiments.
Line 167-170: Totally three batches of HULIS were prepared, and each batch was used for heterogeneous aging experiment incorporating with aerosol online characterization and offline analysis. Each filter sample was characterized in duplicate of redox potential. Molecular composition, cytotoxicity, and lung fluid evolution of the fresh and aged HULIS were tested for at least two times.
6. Could you elucidate how the lung fluid mimics employed in this study accurately represent real-life scenarios?
Answer: Lung fluid, comprising the thin mucus layer in the respiratory tract and alveoli, plays a vital role in trapping particles and maintaining respiratory health and function. As stated in Line 355-357, the real lung fluid is a complicated chemical mixture with varying antioxidants, surfactants, and proteins and involving interactions with the alveoli epithelial cells. The simple lung fluid mimics following the documented protocols only provide a neutral aqueous environment at 37 oC with and without antioxidants, but it provides insights into the intrinsic redox reactions occurred among the inhaled aerosols.
Overall, we are aware of the limitations of the simplified lung fluid mimics and will consider more representative lung fluids in our following studies.
7. Why was the 4-hour timeframe chosen for the study of HULIS in neutral lung fluid?
Answer: The 4-hour time frame was chosen considering the residence time of inhaled particles in human lung and the equilibrium time of redox reactions within particles (Berlinger et al., 2008; Li et al., 2022; Wei et al., 2020). The retention time in the respiratory system varies with the physiochemical properties of inhaled particles and also with the lung lining fluid. The inhaled particles process the procedures of adsorption, dissociation, and deposition into lung fluid, the particle can also penetrate into/through alveolar cells (Kendall et al., 2004; Morozesk et al., 2021; Pan et al., 2023). The residence time for inhaled particles in lung fluid last from several seconds to tens of hours. Other relevant studies characterizing the ROS generation and cellular toxicity of organic aerosols commonly allow for 3-4 hours or longer time to get equilibrium of redox reactions. We have added a sentence to justify the 4-hour timeframe.
Line 280-281: Previous relevant studies allowed 3-4 hours for redox reactions of organic aerosols in lung fluid environment to achieve equilibrium of ROS generation.
8. It would be beneficial to further explain the implications of the findings and the significance of the observed effects on the antioxidant capacity and redox potential of HULIS aerosols.
Answer: HULIS makes the vital redox active, hydrophilic, and toxic composition in urban and rural PM2.5 (Li et al., 2022; Tan et al., 2016; Xu et al., 2020). The oxidative toxicity (indicated by acellular oxidative potential) from PM2.5 and relevant subfractions have been previously studied, yet, the contrary antioxidizing property of HULIS was overlooked in most atmospheric researches, while the oxidizing and antioxidizing properties depict the overall characters of HULIS and influence its toxic function.
Moreover, redox-active HULIS undergo fast transformation in the atmosphere through diverse reaction pathways, such as nighttime O3 and NO3• reactions and daytime OH• photooxidation. But the dynamic evolution of HULIS redox properties and associated toxicity regarding to these aging channels, as well as the behavior of atmospherically aged HULIS in the respiratory system, were not studied.
For the first time, we investigated the roles of the nighttime O3 and NO3• reactions in modifying the oxidative potential and antioxidant capacity (redox potentials) of HULIS, we found that the modified redox potentials correlate with the endpoint cytotoxicity of HULIS and explain the intrinsic redox reactions within the inhaled HULIS to generate ROS in lung fluids. This study illustrates the dynamic health effect of HULIS, and highlight the importance of considering multiphase chemical pathways that can occur in the atmosphere and in the respiratory system to assess overall health effect of organic aerosols.
9. For the lay reader, a brief explanation about what OP and AOC are and their significance would be helpful. What is the significance of H2O2eq? An introductory sentence might help.
Answer: Exposure to PM2.5 has adverse impact on public health. One of the main toxic mechanisms related to inhaled PM2.5 is oxidative stress that interrupts the balance of reactive oxygen species (ROS) and antioxidant levels in the respiratory system. The excess ROS generation, particularly the dominant H2O2 and O2•-, lead to oxidative damage to cellular components, including cell membranes, mitochondria, and DNA etc. (Line 46-50). An acellular assay via DTT depletion was proposed to weigh the possible oxidative impact, namely oxidative potential, of particulate pollutants. Oxidative Potential (OP) refers to the ability of a substance to induce oxidative toxicity via ROS generation and antioxidant consumption (Line 49-50). Antioxidant Capacity (AOC) quantifies the ability of a substance to act as antioxidant through ROS consumption or/and electron donating (Line 51-53). HULIS has both OP and AOC, the apparent duality rises from the context in which the HULIS component is involved and the reactions it can participate in. However, most studies focused on the OP of PM2.5 while overlooking its AOC, thus, these studies provide skewed understanding of PM2.5’s role in the respiratory system (Line 60-61). Our study investigates the dynamic changes of HULIS OP and AOC in the air and in lung fluid environment, the results comprehend the views of HULIS toxicity.
H2O2eq represents the total ROS (dominant H2O2, O2•-, and possibly minor OH•) generated from HULIS via redox reactions between oxidizing and antioxidant components in lung fluid environment (Line 132). ROS generation is the result and also the cause of particle oxidative toxicity. H2O2 is the most abundant and central ROS and cause for oxidative stress in the respiratory tract (Line 312-315).
10. For clarity, provide a brief explanation or definition about what redox proxies are and their relevance.
Answer: The redox proxies (Line 303) mean chemicals that have redox characters and are analogs of HULIS. In this study, we propose that HULIS bears both oxidative potential (OP) and antioxidant capacity (AOC). The OP of HULIS is attributed mainly to oxidizing species of quinones, and it was quantified compared to a standard of 1,4-naphthaquinone (Line 216 and Figure 3), while the AOC of HULIS raised from polyphenolic compositions and was quantified compared to gallic acid and trolox (GAE and TEAC). In short, quinones and gallic acid can represent the oxidizing and antioxidizing compositions of HULIS, correspondingly. Because of the chemical complexity of HULIS, we used a mixture of standard quinone (1,4-naphthaquinone) and gallic acid to represent HULIS in a parallel experiment, and the mixture perfectly replicated the results of HULIS in lung fluids, indicating that redox reactions between oxidizing and antioxidant compositions can explain the evolution mechanisms of HULIS.
 
Reference:
Abatzoglou, J.T., Battisti, D.S., Williams, A.P., Hansen, W.D., Harvey, B.J., Kolden, C.A., 2021. Projected increases in western US forest fire despite growing fuel constraints. Communications Earth & Environment 2, 227.
Alizadeh, M.R., Abatzoglou, J.T., Luce, C.H., Adamowski, J.F., Farid, A., Sadegh, M., 2021. Warming enabled upslope advance in western US forest fires. Proceedings of the National Academy of Sciences 118, e2009717118.
Baduel, C., Monge, M.E., Voisin, D., Jaffrezo, J.-L., George, C., Haddad, I.E., Marchand, N., D’Anna, B., 2011. Oxidation of atmospheric humic like substances by ozone: a kinetic and structural analysis approach. Environmental science & technology 45, 5238–5244.
Baker, K.R., Woody, M.C., Tonnesen, G.S., Hutzell, W., Pye, H.O.T., Beaver, M.R., Pouliot, G., Pierce, T., 2016. Contribution of regional-scale fire events to ozone and PM2. 5 air quality estimated by photochemical modeling approaches. Atmospheric Environment 140, 539–554.
Berlinger, B., Ellingsen, D.G., Náray, M., Záray, G., Thomassen, Y., 2008. A study of the bio-accessibility of welding fumes. Journal of Environmental Monitoring 10, 1448–1453.
Bertram, T.H., Thornton, J.A., 2009. Toward a general parameterization of N2O5 reactivity on aqueous particles: the competing effects of particle liquid water, nitrate and chloride. Atmospheric Chemistry and Physics 9, 8351–8363.
Bruns, E.A., El Haddad, I., Keller, A., Klein, F., Kumar, N.K., Pieber, S.M., Corbin, J.C., Slowik, J.G., Brune, W.H., Baltensperger, U., 2015. Inter-comparison of laboratory smog chamber and flow reactor systems on organic aerosol yield and composition. Atmospheric Measurement Techniques 8, 2315–2332.
Escorcia, E.N., Sjostedt, S.J., Abbatt, J.P., 2010. Kinetics of N2O5 hydrolysis on secondary organic aerosol and mixed ammonium bisulfate− secondary organic aerosol particles. The Journal of Physical Chemistry A 114, 13113–13121.
Galib, M., Limmer, D.T., 2021. Reactive uptake of N2O5 by atmospheric aerosol is dominated by interfacial processes. Science 371, 921–925.
Hodshire, A.L., Akherati, A., Alvarado, M.J., Brown-Steiner, B., Jathar, S.H., Jimenez, J.L., Kreidenweis, S.M., Lonsdale, C.R., Onasch, T.B., Ortega, A.M., 2019. Aging effects on biomass burning aerosol mass and composition: A critical review of field and laboratory studies. Environmental science & technology 53, 10007–10022.
Jahl, L.G., Bowers, B.B., Jahn, L.G., Thornton, J.A., Sullivan, R.C., 2021. Response of the Reaction Probability of N2O5 with Authentic Biomass-Burning Aerosol to High Relative Humidity. ACS Earth and Space Chemistry 5, 2587–2598.
Kang, E., Root, M.J., Toohey, D.W., Brune, W.H., 2007. Introducing the concept of potential aerosol mass (PAM). Atmospheric Chemistry and Physics 7, 5727–5744.
Kendall, M., Guntern, J., Lockyer, N.P., Jones, F.H., Hutton, B.M., Lippmann, M., Tetley, T.D., 2004. Urban PM2. 5 surface chemistry and interactions with bronchoalveolar lavage fluid. Inhalation toxicology 16, 115–128.
Knopf, D.A., Forrester, S.M., Slade, J.H., 2011. Heterogeneous oxidation kinetics of organic biomass burning aerosol surrogates by O3, NO2, N2O5, and NO3. Physical Chemistry Chemical Physics 13, 21050–21062.
Konovalov, I.B., Beekmann, M., D’anna, B., George, C., 2012. Significant light induced ozone loss on biomass burning aerosol: Evidence from chemistry‐transport modeling based on new laboratory studies. Geophysical research letters 39.
Krall, J.R., Anderson, G.B., Dominici, F., Bell, M.L., Peng, R.D., 2013. Short-term exposure to particulate matter constituents and mortality in a national study of US urban communities. Environmental health perspectives 121, 1148–1153.
Li, C., Fang, Z., Czech, H., Schneider, E., Rüger, C.P., Pardo, M., Zimmermann, R., Chen, J., Laskin, A., Rudich, Y., 2022. pH modifies the oxidative potential and peroxide content of biomass burning HULIS under dark aging. Science of The Total Environment 834, 155365.
Li, M., Su, H., Li, G., Ma, N., Pöschl, U., Cheng, Y., 2019. Relative importance of gas uptake on aerosol and ground surfaces characterized by equivalent uptake coefficients. Atmospheric Chemistry and Physics 19, 10981–11011.
Li, X., Zhang, Q., Zhang, Y., Zheng, B., Wang, K., Chen, Y., Wallington, T.J., Han, W., Shen, W., Zhang, X., 2015. Source contributions of urban PM2. 5 in the Beijing–Tianjin–Hebei region: Changes between 2006 and 2013 and relative impacts of emissions and meteorology. Atmospheric Environment 123, 229–239.
Martins, N.R., Da Graca, G.C., 2018. Impact of PM2. 5 in indoor urban environments: A review. Sustainable Cities and Society 42, 259–275.
Morozesk, M., da Costa Souza, I., Fernandes, M.N., Soares, D.C.F., 2021. Airborne particulate matter in an iron mining city: Characterization, cell uptake and cytotoxicity effects of nanoparticles from PM2. 5, PM10 and PM20 on human lung cells. Environmental Advances 6, 100125.
Mozurkewich, M., Calvert, J.G., 1988. Reaction probability of N2O5 on aqueous aerosols. Journal of Geophysical Research: Atmospheres 93, 15889–15896.
Nash, D.G., Tolocka, M.P., Baer, T., 2006. The uptake of O3 by myristic acid–oleic acid mixed particles: evidence for solid surface layers. Physical Chemistry Chemical Physics 8, 4468–4475.
Nema, P., Nema, S., Roy, P., 2012. An overview of global climate changing in current scenario and mitigation action. Renewable and Sustainable Energy Reviews 16, 2329–2336.
O’Brien, R.E., Neu, A., Epstein, S.A., MacMillan, A.C., Wang, B., Kelly, S.T., Nizkorodov, S.A., Laskin, A., Moffet, R.C., Gilles, M.K., 2014. Physical properties of ambient and laboratory‐generated secondary organic aerosol. Geophysical Research Letters 41, 4347–4353.
Pan, D., Xu, Y., Wang, X., Wang, L., Yan, J., Shi, D., Yang, M., Chen, M., 2023. Evaluation the in vivo behaviors of PM2. 5 in rats using noninvasive PET imaging with mimic particles. Chemosphere 339, 139663.
Rudich, Y., Donahue, N.M., Mentel, T.F., 2007. Aging of organic aerosol: Bridging the gap between laboratory and field studies. Annu. Rev. Phys. Chem. 58, 321–352.
Saathoff, H., Naumann, K.-H., Riemer, N., Kamm, S., Möhler, O., Schurath, U., Vogel, H., Vogel, B., 2001. The loss of NO2, HNO3, NO3/N2O5, and HO2/HOONO2 on soot aerosol: A chamber and modeling study. Geophysical Research Letters 28, 1957–1960.
Simonen, P., Saukko, E., Karjalainen, P., Timonen, H., Bloss, M., Aakko-Saksa, P., Rönkkö, T., Keskinen, J., Dal Maso, M., 2017. A new oxidation flow reactor for measuring secondary aerosol formation of rapidly changing emission sources. Atmospheric Measurement Techniques 10, 1519–1537.
Singh, N., Banerjee, T., Raju, M.P., Deboudt, K., Sorek-Hamer, M., Singh, R.S., Mall, R.K., 2018. Aerosol chemistry, transport, and climatic implications during extreme biomass burning emissions over the Indo-Gangetic Plain. Atmospheric Chemistry and Physics 18, 14197–14215.
Singh, S., 2022. Forest fire emissions: A contribution to global climate change. Frontiers in Forests and Global Change 5, 925480.
Southerland, V.A., Brauer, M., Mohegh, A., Hammer, M.S., Van Donkelaar, A., Martin, R.V., Apte, J.S., Anenberg, S.C., 2022. Global urban temporal trends in fine particulate matter (PM2· 5) and attributable health burdens: estimates from global datasets. The Lancet Planetary Health 6, e139–e146.
Tan, J., Xiang, P., Zhou, X., Duan, J., Ma, Y., He, K., Cheng, Y., Yu, J., Querol, X., 2016. Chemical characterization of humic-like substances (HULIS) in PM2. 5 in Lanzhou, China. Science of the Total Environment 573, 1481–1490.
Thornton, J.A., Braban, C.F., Abbatt, J.P., 2003. N2O5 hydrolysis on sub-micron organic aerosols: the effect of relative humidity, particle phase, and particle size. Physical Chemistry Chemical Physics 5, 4593–4603.
Ward, T., Noonan, C., 2008. Results of a residential indoor PM2. 5 sampling program before and after a woodstove changeout. Indoor air 18, 408.
Wei, J., Fang, T., Wong, C., Lakey, P.S., Nizkorodov, S.A., Shiraiwa, M., 2020. Superoxide formation from aqueous reactions of biogenic secondary organic aerosols. Environmental Science & Technology 55, 260–270.
Wen, M., Li, R., Zhang, T., Ding, C., Hu, Y., Mu, R., Liang, M., Ou, T., Long, B., 2022. A potential source of tropospheric secondary organic aerosol precursors: The hydrolysis of N2O5 in water dimer and small clusters of sulfuric acid. Atmospheric Environment 287, 119245.
Xu, X., Lu, X., Li, X., Liu, Y., Wang, X., Chen, H., Chen, J., Yang, X., Fu, T.-M., Zhao, Q., 2020. ROS-generation potential of Humic-like substances (HULIS) in ambient PM2. 5 in urban Shanghai: Association with HULIS concentration and light absorbance. Chemosphere 256, 127050.

22-Oct-2023

Dear Dr Rudich:

Manuscript ID: EA-ART-07-2023-000104.R1
TITLE: Atmospheric Aging Modifies the Redox Potential and Toxicity of Humic-like Substances (HULIS) from Biomass Burning

Thank you for submitting your revised manuscript to Environmental Science: Atmospheres. I am pleased to accept your manuscript for publication in its current form. I have copied any final comments from the reviewer(s) below.

You will shortly receive a separate email from us requesting you to submit a licence to publish for your article, so that we can proceed with the preparation and publication of your manuscript.

You can highlight your article and the work of your group on the back cover of Environmental Science: Atmospheres. If you are interested in this opportunity please contact the editorial office for more information.

Promote your research, accelerate its impact – find out more about our article promotion services here: https://rsc.li/promoteyourresearch.

We will publicise your paper on our Twitter account @EnvSciRSC – to aid our publicity of your work please fill out this form: https://form.jotform.com/211263048265047

How was your experience with us? Let us know your feedback by completing our short 5 minute survey: https://www.smartsurvey.co.uk/s/RSC-author-satisfaction-energyenvironment/

By publishing your article in Environmental Science: Atmospheres, you are supporting the Royal Society of Chemistry to help the chemical science community make the world a better place.

With best wishes,

Dr Lin Wang
Associate Editor, Environmental Science: Atmospheres

Environmental Science: Atmospheres is accompanied by companion journals Environmental Science: Nano, Environmental Science: Processes and Impacts, and Environmental Science: Water Research; publishing high-impact work across all aspects of environmental science and engineering. Find out more at: http://rsc.li/envsci

Reviewer 2

All my queries had been addressed. There was no more comment from me.