From the journal Environmental Science: Atmospheres Peer review history

14-May-2022

Dear Dr Nenes:

Manuscript ID: EA-ART-03-2022-000031
TITLE: Secondary aerosol formation during the dark oxidation of biomass burning emissions

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.

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Associate Editor, Environmental Sciences: Atmospheres

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Reviewer 1

Review on Secondary aerosol formation during the dark oxidation of biomass burning emissions for John K. Kodros
The manuscript performed atmospheric simulation chamber experiments on the chemical oxidation of biomass burning emissions under dark conditions. The author found that oxidation through reactions with the NO3 radical is an additional secondary aerosol formation pathway in biomass burning emission plumes that should be accounted for in atmospheric chemical-transport models. They also found that the biomass burning aerosol pH could promotes inorganic nitrate partitioning to the particulate phase, potentially contributing to the buildup of nitrate aerosol in the boundary layer and enhancing long-range transport. The manuscript is of great scientific interest and can provide unique data and novel findings for the dark oxidation process of biomass burning emissions. Overall, the manuscript should be accepted after addressing the following minor issues.
1. Page 4, the author should remove one “that” in “Observations and model studies to date support that that ambient aerosol dominated by biomass burning emissions tends to exhibit elevated levels of pH compared to other aerosol types.”
2. Page 8, the author should add a more detail description of how to calculate the two mass spectra theta angle, and give some examples.
3. Section 2.4. How does the author measure the concentration of Na+, it could not be ignored, and also could not be measured by AMS.
4. Page 11, the second paragraph, note to use subscripts for CO2+; page 12, the last paragraph, note to use the subscripts for JNO2.
5. Page 13. “The fresh bbOA AMS mass spectrum exhibited moderate variability across the various…degrees with a standard deviation of 6 degrees).” The author should explain why among the dark oxidation experiments, the produced bbSOA spectrum tended to be more similar, but the average theta angle of fresh bbOA between pairs of experiments is 12.5.
6. Section 3.4, last paragraph, and in “Conclusion” section (page 18), pay attention to distinction α- pinene and a-pinene.
7. The manuscript lacks the “Discussion” section about the results, in addition, the “Conclusion” part is too long.
8. In Conclusion section, last sentence, the author only analyzed the aging of BB emissions process with NO3 without light, it could represent the night, but not the winter, so this sentence is not rigorous. The author needs more experiments to verify the oxidation in winter.

Reviewer 2

This study showed the evidence of significant secondary aerosol formation from residential biomass burning under the dark condition based on the chamber experiments. It emphasizes the necessity to include the dark oxidization of biomass burning in the chemical transport models. Three minor comments are suggested as follows.
1. The chamber environment roughly represented the condition of residential wood stove. It is necessary to convey this information in the title, abstract or the significance statement.
2. The dark oxidation of BB plumes was reported in Decker et al. (2019) and Tiitta et al. (2016) as mentioned in the section of Introduction. Any similar or different conclusion was found in this study compared with previous studies?
3. The vapor wall loss and instrumental tube loss of semi-volatile organic may underestimate the secondary organic aerosol formation in the chamber study (Bian et al., 2017; Deming et al., 2019; Pagonis, et al, 2017). As authors only correct the particle wall loss in the study, would the vapor wall loss or tube loss of semi-volatile organics also influence the results of this study?
References:
Bian, Q et al: Secondary Organic Aerosol Formation in Biomass-Burning Plumes: Theoretical Analysis of Lab Studies and Ambient Plumes. Atmos. Chem. Phys. 2017, 17 (8), 5459−5475.
Decker et al.: Nighttime Chemical Transformation in Biomass Burning Plumes: A Box Model Analysis Initialized with Aircraft Observations, Environ. Sci. Technol., 2019, 53, 2529–2538.
Deming, B. L et al.: Measurements of Delays of Gas-Phase Compounds in a Wide Variety of Tubing Materials due to Gas−wall Interactions. Atmos. Meas. Tech. 2019, 12 (6), 3453−3461.
Pagonis, D et al: Effects of Gas−wall Partitioning in Teflon Tubing and Instrumentation on Time-Resolved Measurements of Gas-Phase Organic Compounds. Atmos. Meas. Tech. 2017, 10 (12), 4687−4696.
Tiitta, et al.: Transformation of Logwood Combustion Emissions in a Smog Chamber: Formation of Secondary Organic Aerosol and Changes in the Primary Organic Aerosol Upon Daytime and Nighttime Aging, Atmos. Chem. Phys., 2016, 16, 13251–13269.

We thank both Reviewers for their helpful comments and suggestions. We have addressed all comments here and made the corresponding changes in the revised paper (please see the “tracked changes” version of the main text). In our response, we have copied the original text for the reviewers and give our response below each comment.

Referee 1
The manuscript performed atmospheric simulation chamber experiments on the chemical oxidation of biomass burning emissions under dark conditions. The author found that oxidation through reactions with the NO3 radical is an additional secondary aerosol formation pathway in biomass burning emission plumes that should be accounted for in atmospheric chemical-transport models. They also found that the biomass burning aerosol pH could promote inorganic nitrate partitioning to the particulate phase, potentially contributing to the buildup of nitrate aerosol in the boundary layer and enhancing long-range transport. The manuscript is of great scientific interest and can provide unique data and novel findings for the dark oxidation process of biomass burning emissions. Overall, the manuscript should be accepted after addressing the following minor issues.

1. Page 4, the author should remove one “that” in “Observations and model studies to date support that that ambient aerosol dominated by biomass burning emissions tends to exhibit elevated levels of pH compared to other aerosol types.”

We have corrected the text.

2. Page 8, the author should add a more detail description of how to calculate the two mass spectra theta angle, and give some examples.

We have added the equation used to calculate the theta angle and provided an explicit description of this metric to complement our qualitative discussion. We have also included an example from a previous laboratory study that reports the theta angle between fresh and aged cooking organic aerosol.

3. Section 2.4. How does the author measure the concentration of Na+, it could not be ignored, and also could not be measured by the AMS.

The lack of Na+ measurements is a limitation of this analysis as it is not measured by the AMS. However, the contribution of Na+ to the overall thermodynamics of this specific aerosol system is minor. The main non-volatile cation in biomass burning aerosol is potassium, which is addressed in the manuscript through several sensitivities studies. We have added a statement to the main text indicating this limitation.

4. Page 11, the second paragraph, note to use subscripts for CO2+; page 12, the last paragraph, note to use the subscripts for JNO2.

We corrected these two typos and ensured all other chemical formulae are formatted correctly.

5. Page 13. “The fresh bbOA AMS mass spectrum exhibited moderate variability across the various…degrees with a standard deviation of 6 degrees).” The author should explain why among the dark oxidation experiments, the produced bbSOA spectrum tended to be more similar, but the average theta angle of fresh bbOA between pairs of experiments is 12.5.

We have added the following sentence explaining a likely cause of the increase in similarity across the aged bbOA spectra relative the fresh bbOA spectra:
“This increase in similarity may be due to the increasing prominence of OA mass at m/z 28 (CO+), 29 (CHO+), and 44 (CO2+) in all aged bbOA spectra.”

6. Section 3.4, last paragraph, and in “Conclusion” section (page 18), pay attention to distinction α- pinene and a-pinene.

We have ensured that all references to this monoterpene are formatted as “α-pinene”.

7. The manuscript lacks the “Discussion” section about the results, in addition, the “Conclusion” part is too long.

We prefer not to have a separate Discussion section. Instead, we offer commentary on our results throughout the results section and discuss the implications of our conclusions in the final section (which we have now labeled “Conclusions and Implications”).

8. In Conclusion section, last sentence, the author only analyzed the aging of BB emissions process with NO3 without light, it could represent the night, but not the winter, so this sentence is not rigorous. The author needs more experiments to verify the oxidation in winter.

This is a fair comment. While our work suggests that oxidation through the NO3 radical may play some role in low light conditions, we agree with the reviewer that we have not systematically tested the potential contribution of this oxidation pathway relative to OH concentrations in low-light conditions. We have deleted this reference to winter conditions to avoid over interpretation of our results.




Referee 2
This study showed the evidence of significant secondary aerosol formation from residential biomass burning under the dark condition based on the chamber experiments. It emphasizes the necessity to include the dark oxidization of biomass burning in the chemical transport models. Three minor comments are suggested as follows.

1. The chamber environment roughly represented the condition of residential wood stove. It is necessary to convey this information in the title, abstract or the significance statement.

This is a valid point. We have revised the title, abstract, and significance statement to explicitly state we investigated the oxidation of residential biomass burning emissions.

2. The dark oxidation of BB plumes was reported in Decker et al. (2019) and Tiitta et al. (2016) as mentioned in the section of Introduction. Any similar or different conclusion was found in this study compared with previous studies?

Our results generally agree with the conclusions of these previous studies. Specifically, we note the similarity that biomass burning OA ages under dark conditions in the presence of the NO3 radical. We also find rapid consumption of phenolic compounds and attribute this to reactions with NO3. We have added a sentence to the Conclusions section stating this.

3. The vapor wall loss and instrumental tube loss of semi-volatile organic may underestimate the secondary organic aerosol formation in the chamber study (Bian et al., 2017; Deming et al., 2019; Pagonis, et al, 2017). As authors only correct the particle wall loss in the study, would the vapor wall loss or tube loss of semi-volatile organics also influence the results of this study?

Vapor losses are a common source of uncertainty in environmental smog chamber experiments. In our experimental setup, we estimate that the timescale for vapor wall loss is slow relative our experimental time scale, and does not play a dominant role in influencing the total mass of the bbOA. We determined this through separate control experiments where we injected only biomass burning emissions into the chamber and characterized them for several hours without additional perturbations (one such experiment, Experiment 10, is included in this study). However, we do note that vapor wall loss may play some role in affecting the chemical characteristics of OA in our experiments beyond what is observable with the AMS. A detailed analysis of these processes is beyond the scope of the present study, but is being investigated in a separate study.
We agree with the reviewer that tube loss of semi-volatile organics prior to injection in the experimental chamber may take place and alter the volatility of the fresh biomass burning emissions. Given the large dilution rates in the ambient atmosphere, loss of semi-volatile species prior to the injection may increase the similarity of our experimental results with the ambient atmosphere. A quantitative answer to this question is again beyond the scope of the present study; however, we have added a statement to the limitations paragraph to highlight this potential source of uncertainty.

29-Jul-2022

Dear Dr Nenes:

Manuscript ID: EA-ART-03-2022-000031.R1
TITLE: Secondary aerosol formation during the dark oxidation of biomass burning emissions

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.

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Dr Nønne Prisle
Associate Editor, Environmental Sciences: Atmospheres

Reviewer 1

I have no more questions. I agree that this article is accepted by the Environmental Sciences: Atmospheres