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Peer-Review Record

Photooxidation of Emissions from Firewood and Pellet Combustion Using a Photochemical Chamber

Atmosphere 2019, 10(10), 575; https://doi.org/10.3390/atmos10100575
Reviewer 1: Anonymous
Reviewer 2: Anonymous
Reviewer 3: Anonymous
Atmosphere 2019, 10(10), 575; https://doi.org/10.3390/atmos10100575
Received: 14 August 2019 / Revised: 4 September 2019 / Accepted: 17 September 2019 / Published: 24 September 2019
(This article belongs to the Section Aerosols)

Round 1

Reviewer 1 Report

The article “Photooxidation of emissions from firewood and pellet combustion using a photochemical chamber” presents the characterization of emissions from firewood and pellet combustion using photochemical chamber. Results highlighted the advantage of using pellets over the firewood as firewood combustion are causing high chamber loadings. Authors also tried to evaluate the aging using tracer signals from the ACSM data which probably needs more explanation and can be done in a better way.

Results shown in the paper is not very precisely highlighted in the abstract. It could be nice to modify the abstract a bit so it can provide more clear information on the work done. Overall, the manuscript is very well written and contains very useful information. Only minor revisions are needed.

 

Line 121: Authors have mentioned about the particle wall losses. Did authors have tried to evaluate the particle wall losses? Was it significant? Have the particle wall loss correction is made while calculating the total particle mass loading? I think it should be mentioned in the manuscript.

 

Line 215: “[33] summarize the photochemical reactions in this chamber. “ Sentence should be modified, I didn’t get what authors have tried to convey.

 

Line 222-227: Authors have discussed about ozone in the chamber. What was the concentration levels of ozone in the chamber?

 

Line 252-255: Authors have suggested to use CO as a qualitative measure of VOC in the chamber? Is there any reference for this? Based on similar behavior, Authors have made this assumption. I think it requires more clarification.

 

Line 317-320: How the authors are very sure that all NO3 measured in the chamber is in the form of organic nitrate? This statement needs strong evidence.

 

Authors have tried to use well known triangle plots to investigate the aging of aerosols. The attempt has been made very nicely. It could be also nice if authors can try to compare their photochemical chambers results with previous lab experiments, and try to add them on the triangle plots. That might give some more useful information on aging.

 

Author Response

Santiago, September 3, 2019

Response to the reviewers

We really appreciate the reviewer’s valuable comments which has contributed enriched the manuscript significantly. Overall,

We have improved the English language, and corrected all the grammatical typos and errors throughout the manuscript. All changes and modifications have been highlight in yellow. We have added several new references to support our conclusions.

Below are the answer details.

Reviewer 1.

The article “Photooxidation of emissions from firewood and pellet combustion using a photochemical chamber” presents the characterization of emissions from firewood and pellet combustion using photochemical chamber. Results highlighted the advantage of using pellets over the firewood as firewood combustion are causing high chamber loadings. Authors also tried to evaluate the aging using tracer signals from the ACSM data which probably needs more explanation and can be done in a better way.

Results shown in the paper is not very precisely highlighted in the abstract. It could be nice to modify the abstract a bit so it can provide more clear information on the work done. Overall, the manuscript is very well written and contains very useful information. Only minor revisions are needed.

We have modified the abstract in order to include a better description of the work done

Line 121: Authors have mentioned about the particle wall losses. Did authors have tried to evaluate the particle wall losses? Was it significant? Have the particle wall loss correction is made while calculating the total particle mass loading? I think it should be mentioned in the manuscript.

We did not perform BC or other measurements that would allow us to calculate wall losses. However, a discussion is provided in line 123 and 300, with an estimation of the wall losses, based on published results (reference 48)

Line 215: “[33] summarize the photochemical reactions in this chamber. “Sentence should be modified, I didn’t get what authors have tried to convey.

Answer: Sentence was changed to: “In Gramsch et al, 2018 [33] there is a summary of the photochemical reactions in this chamber”

Line 222-227: Authors have discussed about ozone in the chamber. What was the concentration levels of ozone in the chamber?

Answer: Yes, it was included, but in corrected version of this manuscript was expanded, due to Review 2 has suggested a quite useful interpretation about this behavior which was included in the corrected version of the manuscript. Initial O3 concentration (prior turn UV lights on) was zero concentration. Ozone and particles concentration before filling the chamber process with biomass combustion emissions was used an indicator of how clean the chamber was. After ~280 min of UV irradiation, only wood filtered emission experiment shown an increase of O3, reaching around 250 ppb.

Line 252-255: Authors have suggested to use CO as a qualitative measure of VOC in the chamber? Is there any reference for this? Based on similar behavior, Authors have made this assumption. I think it requires more clarification.

Answer: Unfortunately, during the experiments we didn’t have the capacity to measure VOC. However, we have incorporated two new references in the corrected manuscript. CO and VOC are emission coming from the same condition (incomplete combustion) we’ve supposed that both have emission rates more or less correlated. In fact, in reference [1] is shown that when both VOC and CO are coming from the same source, a good correlation between them can be found. Here we can see from CO emissions that pellet stove has a real better combustion compared to wood, because its new technology. In reference [2] there is strong evidence that newer improved devices makes combustion process more efficiency and then VOC and CO decreased.

Line 317-320: How the authors are very sure that all NO3 measured in the chamber is in the form of organic nitrate? This statement needs strong evidence.

Answer: Could it be another inorganics cation that could be neutralizing the anions, like K+, Ca+, etc., especially in ashes. Unfortunately, we didn’t have capability to measure it. In atmosphere these ions usually are in ng/m3, and the amount of nitrate found it in experiments were quite over that. On the other hand, it is postulated that most of the NO3 measured by ACSM in the chamber is in the form of organic nitrates. If there is another inorganics cations neutralizing the NO3, those cannot be measured by ACSM, because it only has capability to measure non-refractory PM materials [3], and inorganics salts usually are refractory materials. Also, there is evidence of organics nitrates formation from biogenics VOC oxidation. Reference [4] indicated that at high and even modest concentrations of NOx, the peroxy radicals react primarily with NO, forming mostly NO2 and an alkoxy radical (RO), and one of the following reaction is the addition of the NO to the peroxy radical, giving an organic nitrate (RONO2) product. Organics nitrates was also observed in chamber experiments using high-NOx photooxidation of limonene, α-pinene, Δ-3-carene, and tridecane, contributing significantly to the SOA[5].

Authors have tried to use well known triangle plots to investigate the aging of aerosols. The attempt has been made very nicely. It could be also nice if authors can try to compare their photochemical chambers results with previous lab experiments, and try to add them on the triangle plots. That might give some more useful information on aging.

Answer:

Unfortunately, we don’t have the experimental data for those experiments, so a qualitative tray could be done. However, interpretation of these graphs has been expanded in order to include more references.

 

Reviewer 2 Report

This article uses a photochemical chamber and multiple instruments to analyze the photooxidation of biomass fuel combustion emissions, which is a valuable topic and of scientific significance. The experiments are well designed and the results could provide the community with deeper understandings of the photochemical aging processes of the organic aerosol from two type of major fuel combustions in Chile. However, the interpretation and discussion on the results still need to be significantly improved. I would recommend this article be properly revised before it can be considered for publication in Atmosphere. Please consider the following specific comments.

Do the authors consider quantitatively the wall loss of gases and particles in the chamber? The wall loss might have influence on the gas phase chemistry. Line 261 and Line 271-272. The explanations are not enough persuasive. To the reviewer's understanding, excessive VOC should hamper NO2-OH reation, which cause the restoring of NO2 and formation of O3. The decrease of NO2 might be the result of lower restoring rate (and also the wall loss), which is due to the depletion of VOCs. It is hard to understand why the speeding up of O3 production could lead to the decrease of NO2. The authors use the experimental results of filtered and unfiltered emissions to explore the gas phase chemistry and aging of organic aerosols respectively. Considerable SOA is formed during the photooxidation of filtered emission, while the authors conclude that SOA formation is ignorable for the unfiltered emission. The presence of POA could hinder the formation of SOA with diameter around 20nm, but this does not necessarily mean that the SOA could not be separated from POA. Is it possible to get the SOA formation by combining the results of filtered and unfiltered emission as well as considering the wall loss? The SOA formation from unfiltered emission might have better scientific significance and application value. The authors mention that the initial NOx concentrations have great variety among several experiments with unfiltered emissions. What about the filtered emission? Is there only one set of experiment for the filtered emission? Is it possible that the variation of initial NOx concentration has influence on the extent or pathway of gas phase chemistry? I think there should be some discussion on the uncertainties regarding the conclusions of the experiments for filtered emissions. Please go through the whole manuscripts and correct the grammar errors and typos. e.g. line 192, 264, 267, 317, 433. In addition, the irradiation times in Figure 8 is shown by arrows rather than by gradual colors, which is inconsistent with the text (e.g. line 397). The term NOtmax/NO0 in Table 3 is also inconsistent with the text.

 

Author Response

Santiago, September 3, 2019

Response to the reviewers

We really appreciate the reviewer’s valuable comments which has contributed enriched the manuscript significantly. Overall,

We have improved the English language, and corrected all the grammatical typos and errors throughout the manuscript. All changes and modifications have been highlight in yellow. We have added several new references to support our conclusions.

Below are the answer details.

Reviewer 2.

Open Review

(x) I would not like to sign my review report 
( ) I would like to sign my review report 

English language and style

( ) Extensive editing of English language and style required 
(x) Moderate English changes required 
( ) English language and style are fine/minor spell check required 
( ) I don't feel qualified to judge about the English language and style 

 

 

Yes

Can be improved

Must be improved

Not applicable

Does the introduction provide sufficient background and include all relevant references?

(x)

( )

( )

( )

Is the research design appropriate?

(x)

( )

( )

( )

Are the methods adequately described?

(x)

( )

( )

( )

Are the results clearly presented?

( )

(x)

( )

( )

Are the conclusions supported by the results?

( )

( )

(x)

( )

Comments and Suggestions for Authors

This article uses a photochemical chamber and multiple instruments to analyze the photooxidation of biomass fuel combustion emissions, which is a valuable topic and of scientific significance. The experiments are well designed and the results could provide the community with deeper understandings of the photochemical aging processes of the organic aerosol from two type of major fuel combustions in Chile. However, the interpretation and discussion on the results still need to be significantly improved. I would recommend this article be properly revised before it can be considered for publication in Atmosphere. Please consider the following specific comments.

Do the authors consider quantitatively the wall loss of gases and particles in the chamber? The wall loss might have influence on the gas phase chemistry.

Answer: We did not measure BC or other species to calculate wall losses. However, we have added an estimation of wall loses based on the work by “Wang, N.; Jorga, S. D.; Pierce, J. R.; Donahue, N. M.; and Pandis, S. N. Particle wall-loss correction methods in smog chamber experiments. Atmos. Meas. Tech., 2018, 11, 6577–6588.” Figure 3 has the estimation.

Line 261 and Line 271-272. The explanations are not enough persuasive. To the reviewer's understanding, excessive VOC should hamper NO2-OH reaction, which cause the restoring of NO2 and formation of O3. The decrease of NO2 might be the result of lower restoring rate (and also the wall loss), which is due to the depletion of VOCs. It is hard to understand why the speeding up of O3 production could lead to the decrease of NO2.

The authors use the experimental results of filtered and unfiltered emissions to explore the gas phase chemistry and aging of organic aerosols respectively. Considerable SOA is formed during the photooxidation of filtered emission, while the authors conclude that SOA formation is ignorable for the unfiltered emission. The presence of POA could hinder the formation of SOA with diameter around 20nm, but this does not necessarily mean that the SOA could not be separated from POA. Is it possible to get the SOA formation by combining the results of filtered and unfiltered emission as well as considering the wall loss? The SOA formation from unfiltered emission might have better scientific significance and application value.

Answer: Unfortunately we did not measure SOA formation in the unfiltered emission, because the ACSM was saturated. It is very hard to answer this question.

The authors mention that the initial NOx concentrations have great variety among several experiments with unfiltered emissions. What about the filtered emission? Is there only one set of experiment for the filtered emission? Is it possible that the variation of initial NOx concentration has influence on the extent or pathway of gas phase chemistry? I think there should be some discussion on the uncertainties regarding the conclusions of the experiments for filtered emissions.

Answer: The variability in the unfiltered emissions was even greater than in filtered emissions. The error in the initial NOx concentration is of the order of 100%, so we did not include these data.

Please go through the whole manuscripts and correct the grammar errors and typos. e.g. line 192, 264, 267, 317, 433.

 Answer: Corrected.

In addition, the irradiation times in Figure 8 is shown by arrows rather than by gradual colors, which is inconsistent with the text (e.g. line 397).

 Answer: New updated graphs with gradual colors has been incorporated in corrected version.

The term NOtmax/NO0 in Table 3 is also inconsistent with the text.

 Answer: Corrected. It refers to NO2tmax /NO2o ratio.

If we compare the time to reach the NO2 maximum (Table 3) with the NO consumption curves shown in Figure 6, it is seen that NO consumption appears to be lower in the experiments with pellets than those with firewood. The NO concentrations at each irradiation time (NOt) were normalized by the NO initial concentration (NOo), (NOt/NOo). It is seen that 50–70 min of UV irradiation are needed to obtain 20% of the initial NO concentration in the experiments with firewood, while the experiments with pellets require more than 100 min. These results are consistent with what was determined for the filtered experiments (previous section). The lower efficiency of the combustion in the experiments with firewood emits more VOC than with pellets, and this is reflected in the ozone values.

 

Reviewer 3 Report

This manuscript presents the results of a very interesting study of the photo oxidation of emissions from firewood and pellet combustion using a photochemical chamber. Wood spoke pollution is an issue in many part of the world and as such the finding of this study would be of wide interest. The manuscript is well written and can be published after some minor corrections/clarifications.

Major comments:

Lines 438: “However, in all experiments the concentration levels of the secondary particles were negligible compared to the amount of primary particles, even after ~280 minutes of the UV irradiation.”

While this was in the conclusion, a bit of discussion needs to be presented in the results and discussion section, as in the atmosphere pre-courses would be present which could potentially increase the formation of secondary aerosols.

This is hinted to in the conclusion on Lines 448-449: “This result is not expected to be the atmosphere, so any extrapolation of these experiments should take this into account.”

Minor comments:

In a number of places there was an error with the reference i.e. “Error! Reference source not found”. Line 153: “manually in a bed burner”, do the authors mean “manually on the bed of the burner”? Line 192: “gases)”. There is no corresponding “(“ for “)”. Line 239; It is not explained what the dashes on the red NO2 curve represent. Line 271: “decrease possible because” could read better as “decrease possibly because”. Line 312; Figure 4. It was hard to see the legend – maybe a larger point size will help. Line 433; “Al large” do the authors mean “A large”.

Author Response

Santiago, September 3, 2019

Response to the reviewers

We really appreciate the reviewer’s valuable comments which has contributed enriched the manuscript significantly. Overall,

We have improved the English language, and corrected all the grammatical typos and errors throughout the manuscript. All changes and modifications have been highlight in yellow. We have added several new references to support our conclusions.

Below are the answer details.

Reviewer 3

Open Review

(x) I would not like to sign my review report 
( ) I would like to sign my review report 

English language and style

( ) Extensive editing of English language and style required 
( ) Moderate English changes required 
(x) English language and style are fine/minor spell check required 
( ) I don't feel qualified to judge about the English language and style 

 

 

Yes

Can be improved

Must be improved

Not applicable

Does the introduction provide sufficient background and include all relevant references?

(x)

( )

( )

( )

Is the research design appropriate?

(x)

( )

( )

( )

Are the methods adequately described?

(x)

( )

( )

( )

Are the results clearly presented?

(x)

( )

( )

( )

Are the conclusions supported by the results?

(x)

( )

( )

( )

Comments and Suggestions for Authors

This manuscript presents the results of a very interesting study of the photo oxidation of emissions from firewood and pellet combustion using a photochemical chamber. Wood spoke pollution is an issue in many part of the world and as such the finding of this study would be of wide interest. The manuscript is well written and can be published after some minor corrections/clarifications.

Major comments:

Lines 438: “However, in all experiments the concentration levels of the secondary particles were negligible compared to the amount of primary particles, even after ~280 minutes of the UV irradiation.”

While this was in the conclusion, a bit of discussion needs to be presented in the results and discussion section, as in the atmosphere pre-courses would be present which could potentially increase the formation of secondary aerosols. This is hinted to in the conclusion on Lines 448-449: “This result is not expected to be the atmosphere, so any extrapolation of these experiments should take this into account.”

Answer: The sentence was expanded.

This result could be due to the high primary emission loading reached in the chamber in each experiment which it was not possible to control. High loading from primary emissions could quench the secondary particle formation in several process, and in the atmosphere primary emission is usually efficiency diluted so probably secondary particle formation could be enhanced compared to our results.  

Minor comments:

In a number of places there was an error with the reference i.e. “Error! Reference source not found”.

Answer: Corrected

Line 153: “manually in a bed burner”, do the authors mean “manually on the bed of the burner”?

Answer: Yes, we do. It was modified in corrected version.

Line 192: “gases)”. There is no corresponding “(“ for “)”.

Answer: Corrected

Line 239; It is not explained what the dashes on the red NO2 curve represent.

Answer: Dashes doesn’t mean anything special. It was updated the NO2 curve.

Line 271: “decrease possible because” could read better as “decrease possibly because”.

Answer: Corrected

Line 312; Figure 4. It was hard to see the legend – maybe a larger point size will help.

Answer: Corrected

Line 433; “Al large” do the authors mean “A large”.

Answer: Corrected

 

Round 2

Reviewer 2 Report

The authors have generally addressed my comments.

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