Dear Reviewer,

We sincerely appreciate your thorough review and constructive comments on our manuscript titled "Emission Characteristics and Influencing Factors of Carbonyl Compounds from Four Typical Combustion Sources." We are grateful for your recognition of the manuscript's potential for publication in ACP and for your detailed suggestions, which have significantly improved the quality of our work. Below, we provide a point-by-point response to your comments and outline the revisions we have made accordingly.

Major Point:

1. Distinction between softwood and hardwood (Section 2.1 and Section 3.1):

We sincerely apologize for the oversight in not clearly distinguishing between softwood and hardwood in the original manuscript. In the revised version, we have explicitly differentiated these two fuel types in Section 2.1. Additionally, in Section 3.1, we have added a detailed comparison of the emission characteristics between softwood and hardwood. Our analysis reveals that softwood (e.g., pine) tends to emit higher concentrations of carbonyl compounds, particularly small-molecule carbonyl compounds such as formaldehyde and acetaldehyde, which is likely attributed to differences in lignin content and combustion efficiency. This finding has been discussed in the revised manuscript, along with potential explanations for the observed variations.

Minor Points:

2. Abstract, first sentence:

As suggested, we have rephrased the first sentence of the Abstract to: “Fuel combustions are important primary sources of carbonyl compounds (CCs)…” This revision improves the clarity and precision of the statement.

3. Abstract, line 30:

The word “tend” has been removed as recommended. The revised sentence now reads: “High-temperature promotes small molecules like F+A to cyclize, supplying ample precursors for the formation of acetone and aromatic aldehyde.”

4. Use of “EF_CCs” abbreviation:

We have carefully reviewed the manuscript and replaced all instances of “EFs of CCs” with “EF_CCs” to ensure consistency. This change has been applied throughout the text.

5. Repeated definitions of abbreviations:

We apologize for the redundancy in defining abbreviations. In the revised manuscript, we have ensured that each abbreviation (e.g., CCs, EFs) is defined only once upon its first appearance.

6. Grammar mistakes:

We sincerely apologize for the grammatical errors in the original manuscript. The following corrections have been made: 

   “Fuel types is key factors…” has been corrected to “Fuel type is a key factor…” 

   “Fuel types determines the composition of…” has been corrected to “Fuel type determines the composition of…” 

All other instances of subject-verb disagreement have been carefully reviewed and corrected.

7. Equations in Page 5:

Thank you for pointing out the inconsistency in the use of hyphens and minus signs in the equations. We have revised the equations to use hyphens for subscripts (e.g., c-­­­­fuel) and minus signs for mathematical operations, ensuring clarity and consistency.­

8. Explanation of “bell-shaped distribution theory” (Page 7):

We have added a brief explanation of the “bell-shaped distribution theory” in the revised manuscript. Specifically, we describe it as a theoretical framework used to explain the relationship between the volatile content of residential coal and its emission characteristics, where emissions peak at intermediate volatile content and decrease at both very high and very low volatile content levels. This addition provides better context for readers unfamiliar with the concept.

Additional Revisions:

In addition to addressing your specific comments, we have conducted a thorough proofreading of the manuscript to correct any remaining grammatical errors, improve sentence structure, and ensure consistency in terminology and formatting. We have also double-checked all abbreviations, equations, and references to ensure accuracy.

Once again, we deeply appreciate your time and effort in reviewing our manuscript. Your insightful comments have greatly enhanced the clarity, rigor, and overall quality of our work. We hope that the revised manuscript now meets the high standards of ACP and look forward to your feedback.

Sincerely, 

Yanjie Lu

On behalf of all authors

Dear Reviewer,

We sincerely appreciate your thorough and constructive review of our manuscript titled "Emission Characteristics and Influencing Factors of Carbonyl Compounds from Various Typical Combustion Sources." We are grateful for your recognition of the manuscript's potential contribution to air pollution control and management, as well as for your detailed suggestions, which have significantly improved the quality of our work. Below, we provide a point-by-point response to your comments and outline the revisions we have made accordingly.

Minor Comments:

1. Abstract revision:

We have revised the Abstract to better highlight the scientific innovation and applied value of this study. Specifically, we have explicitly stated its contributions to optimizing combustion systems, guiding emission control policies, and enhancing atmospheric chemistry modeling frameworks. The revised Abstract now reads: 

“This study provides the latest data for emission inventories and offers a scientific basis for targeted emission reduction strategies. Its findings contribute to optimizing combustion systems, guiding emission control policies, and enhancing atmospheric chemistry modeling frameworks.”

1. Conclusion section enhancement:

As suggested, we have added specific estimates of the emission reduction effects of the proposed measures on atmospheric oxidizing capacity. For example, we have quantified the impact of increasing combustion temperature and upgrading emission standards on ozone (O₃) formation. The revised Conclusion now includes: 

“At a high combustion temperature of 800°C, the ozone formation potentials (OFP) of BB and RCC are 0.8 (g O₃/kg-fuel) and 0.6 (g O₃/kg-fuel), respectively, indicating that increasing the combustion temperature can reduce ozone formation by 91.0% and 53.8%, respectively. Similarly, for both on-road and non-road sources, upgrading vehicle emission standards can significantly reduce ozone formation (46.8%~65.0%), with the most notable reduction effects observed for DV (63.6% reduction) and AM (65.0% reduction), which are the sources with higher emission levels. In conclusion, the proposed measures in this study demonstrate significant emission reduction effects on atmospheric oxidizing capacity. ”

1. Spelling errors:

We sincerely apologize for the spelling error in line 32 of the Abstract. The word “allevite” has been corrected to “alleviate.”

1. Terminology standardization:

We have ensured that “EF_CCs” is defined upon its first appearance and used consistently throughout the manuscript. Additionally, In the fields of chemistry and environmental science, “AA” is a commonly used abbreviation for aromatic aldehydes. However, to avoid confusion with other terms, its definition has been explicitly stated upon its first use in this manuscript. Therefore, “AA” has been retained as the abbreviation for aromatic aldehydes in this article. As for “OA”, which represents "other aldehydes and ketones" in this study, it is indeed prone to confusion with "organic aerosols" (OA). To address this, the term "other aldehydes and ketones" has been replaced with “Other CCs” throughout the manuscript.

1. Sentence structure simplification:

We have simplified lengthy and complex sentences to improve readability. For instance, the second paragraph of the Introduction (line 49) has been broken into multiple sentences. The revised Abstract now reads:

“Cheng et al. (2022) investigated the emission characteristics of CCs from BB, such as emission factors (EFs) and chemical composition, using a tube-furnace. They found that combustion conditions, including temperature and oxygen concentration, as well as fuel characteristics like composition, significantly affect the EFs and composition of CCs.”

We have also added the suggested reference: 

“Emission of Intermediate Volatile Organic Compounds from Animal Dung and Coal Combustion and Its Contribution to Secondary Organic Aerosol Formation in Qinghai-Tibet Plateau, China. Environmental Science & Technology 2024 58 (25), 11118-11127.”

1. Biomass sample selection and combustion process accuracy:

We acknowledge the concern regarding the selection of 2g biomass samples and the rapid combustion process. To ensure sampling accuracy, we have implemented a continuous sampling protocol and validated it through repeated experiments. We have also cited the following reference to support our methodology: 

“Examination of long-time aging process on volatile organic compounds emitted from solid fuel combustion in a rural area of China. Chemosphere 333 (2023) 138957.”

1. Consistency in font size:

We have ensured that the font size in all figures and tables is consistent. For example, the legend font size in Figure 1a has been adjusted to match the other subfigures, presenting a more organized and visually appealing layout.

1. Uncertainty quantification and schematic diagram:

We have added (1) uncertainty quantification analyses of ozone formation potential across diverse CCs emission sources, and (2) a schematic diagram of the sampling system in Section 2.1 to enhance methodological transparency. The schematic diagram illustrates the sampling setup and process, providing readers with a clear understanding of the experimental design. Here are some of the new additions:

Uncertainty quantification analyse:

该表显示了不同燃烧源的臭氧形成潜力估计的不确定性范围，以最大 （Max） 和最小 （Min） 偏差百分比表示。可以观察到，偏差通常与羰基化合物的排放因子呈正相关，这意味着排放因子越高，燃烧源计算的臭氧形成潜力的不确定性就越大。其中，BB、RCC 和 RCC 被确定为高不确定性燃烧源，表明它们的排放特性很复杂，可能显着促进臭氧的形成。建议对这些燃烧源的排放因子进行更精确的测量和建模，以减少不确定性。

The uncertainty analysis and the schematic diagram of the sampling system have been added to the supplementary materials.

1. Figure resolution improvement:

All figures have been replaced with higher resolution versions to ensure graphical clarity essential for proper interpretation of the experimental data.

Additional Revisions:

In addition to addressing your specific comments, we have conducted a thorough proofreading of the manuscript to correct any remaining grammatical errors, improve sentence structure, and ensure consistency in terminology and formatting. We have also double-checked all abbreviations, equations, and references to ensure accuracy.

Once again, we deeply appreciate your time and effort in reviewing our manuscript. Your insightful comments have greatly enhanced the clarity, rigor, and overall quality of our work. We hope that the revised manuscript now meets the high standards of Atmospheric Chemistry and Physics and look forward to your feedback.

Sincerely, 

Yanjie Lu

On behalf of all authors

Dear Reviewer,

We sincerely thank the reviewer for their thorough and constructive feedback on our manuscript. We greatly appreciate the time and effort dedicated to evaluating our work and providing valuable suggestions for improvement. Below, we address each of the reviewer’s comments in detail and outline the revisions made to the manuscript.

Minor Comments

1. Comment on the detailed classification of fuel types and results discussion:

We appreciate the reviewer’s observation regarding the finer distinctions in fuel types, such as differences in carbonyl compounds (CCs) emissions between southern and northern straw burning, as well as between softwood and hardwood. In response, we have expanded the Results and Discussion section to include a more detailed analysis of these distinctions. Specifically, we have added a subsection comparing the emission characteristics of CCs from southern and northern straw burning, as well as softwood versus hardwood combustion. These additions are supported by additional data and references to relevant studies. Below is a brief description of the newly added content:

The carbonyl compounds generated from the combustion of southern straw (rice straw) are higher than those from northern straw. The emission factor of CC from rice straw combustion (3865.6 ± 558 mg/kg) is significantly higher than that of corn (2829.8 ± 1771.8 mg/kg) and wheat (1772.6 ± 847.2 mg/kg), indicating that the carbonyl compounds generated from southern straw combustion are 1.4-2.2 times higher than those from northern straw combustion. This phenomenon may be attributed to differences in the content of biomass components (cellulose, hemicellulose, and lignin) and combustion efficiency. Cheng et al. (2022) found that among the three biomass components, cellulose combustion generates the highest amount of CCs, followed by hemicellulose, with lignin producing the least. Meanwhile, Zhao et al. (2019) discovered that the holocellulose content (cellulose + hemicellulose: ~56.3%) of rice straw is higher than that of corn and wheat. Additionally, in this study, the combustion efficiency of rice straw (90.9%) is slightly lower than that of corn and wheat (92.0%-92.8%).

The carbonyl compounds generated from the combustion of softwood (pine) are higher than those from hardwood. The emission factor of CCs from pine combustion (1415.3 ± 431.8 mg/kg) is significantly higher than that of poplar (1020.3 ± 249.1 mg/kg) and willow (905.5 ± 109.6 mg/kg), indicating that the carbonyl compounds generated from softwood combustion are 1.4-1.6 times higher than those from hardwood. This phenomenon may be due to differences in combustion efficiency. In this study, the combustion efficiency of pine (94.0%) is significantly lower than that of poplar and willow (95.6%-96.0%). Studies have shown that incomplete combustion of fuels is more likely to generate CCs.

1. Comment on the discussion of CCs formation mechanisms for on-road sources:

We agree with the reviewer that the discussion on the formation mechanisms of CCs from on-road sources, particularly for ethanol-blended gasoline and biodiesel, was relatively brief. To address this, we have expanded the discussion in Section 4.2 to include a more detailed analysis of the formation mechanisms of CCs from ethanol-blended gasoline and biodiesel. We have also added relevant references to support this discussion, ensuring a more comprehensive understanding of the underlying processes.

For the ethanol gasoline section, an in-depth discussion on different emission standards has been added. It was found that the "acetaldehyde/formaldehyde" ratio in carbonyl compounds emitted by China VI emission standard ethanol gasoline vehicles is approximately 0.38, which is about 2.5 times that of gasoline vehicles under the same emission standard. This indicates that the use of ethanol gasoline significantly increases acetaldehyde emissions. In contrast, this ratio for China V ethanol gasoline vehicles is 1.80, suggesting that higher emission standards can effectively reduce carbonyl compound emissions while also decreasing acetaldehyde generation. The reason for this phenomenon may be that, as emission standards are continuously upgraded, exhaust treatment technologies are improved, and emission requirements become stricter, leading to further oxidation of harmful substances such as acetaldehyde into formaldehyde.

For the biodiesel section, two additional references have been included to enhance the understanding of the formation mechanisms:

Lin, Y.C., Hsu, K.H., and Chen, C.B.: Experimental investigation of the performance and emissions of a heavy-duty diesel engine fueled with waste cooking oil biodiesel/ultra-low sulfur diesel blends, Energy, 36, 241–248, https://doi.org/10.1016/j.

energy.2010.10.045, 2011.

Chien, S.M., Huang, Y.J., Chuang, S.C., and Yang, H.H.: Effects of biodiesel blending on particulate and polycyclic aromatic hydrocarbon emissions in nano/ultrafine/fine/ coarse ranges from diesel engine, Aerosol Air Qual. Res., 9, 18–31, https://doi.org /10.4209/aaqr.2008.09.0040, 2009.

1. Comment on grammatical errors and subject-verb disagreement:

We sincerely apologize for the grammatical errors in the manuscript, particularly the subject-verb disagreement in line 24 of the abstract. The revised Abstract now reads:

“Fuel type is a key factor affecting the CCs components.”

We have conducted a thorough proofreading of the entire manuscript to correct grammatical errors, improve sentence structure, and ensure consistency in language usage. All instances of subject-verb disagreement have been resolved.

1. Comment on the use of EF_CCs and EFs of CCs:

We thank the reviewer for pointing out the inconsistency in the use of EF_CCs and EFs of CCs. As suggested, we have replaced all instances of “EFs of CCs” with “EF_CCs” throughout the manuscript to ensure consistency and clarity.

1. Comment on the annotation of abbreviations:

We apologize for the oversight in not providing the full name for the abbreviation “ES” upon its first occurrence in line 74 of the abstract. We have now clearly annotated all abbreviations with their full names upon their first appearance in the main text. For example, “ES” is now defined as “emission standard” in line 74.

1. Comment on the font format in formulas:

We acknowledge the inconsistency in the font format used in the formulas. To address this, we have standardized the font format for all formulas throughout the manuscript, ensuring a consistent and professional presentation.

Additional Revisions

In addition to addressing the reviewer’s specific comments, we have conducted a thorough review of the manuscript to ensure the accuracy and clarity of all content. This includes: 

- Double-checking all abbreviations, equations, and references for consistency and correctness. 

- Ensuring that all figures and tables are presented with high resolution and clarity. 

- Improving the overall flow and readability of the text by simplifying complex sentences and enhancing logical transitions between sections.

We are deeply grateful for the reviewer’s insightful comments, which have significantly improved the quality of our manuscript. We believe that the revisions made in response to these comments have strengthened the scientific rigor, clarity, and overall presentation of our work. We hope that the revised manuscript now meets the high standards of ACP and look forward to the reviewer’s feedback.

Thank you once again for your valuable time and constructive suggestions.

Sincerely, 

Yanjie Lu 

On behalf of all authors