Review Reports - Estimating Emissions from Crop Residue Open Burning in Central China from 2012 to 2020 Using Statistical Models Combined with Satellite Observations

Round 1

Reviewer 1 Report

It is an interesting work to use Visible Infrared Imaging Radiometer Suite to esimate the open burning proportion and asssociated pollutant emission. The significant decending trend of emission of these air pollutant was addressed, which was valuable. While the manscript need to be reshaped and improved before it could be accepted for publication.

Comments:

(1) All results in the paper did not verified by any ground investigation. The trend of emission could be fine but the number and the uncertainty could not be evaluated.

(2) The emission coefficiency and the uncertainty of the pollutants from burning crop residue would related to the dryness and compactness of the residue, which should be estimated by either satellite data or ground observation.

(3) The results of the paper could be compared with other air pollutant data set, such as AOD.

Author Response

#Reviewer 1:

Response: Thanks for your constructive suggestions. We have made a major revision according to your comments.

Point 1: All results in the paper did not verified by any ground investigation. The trend of emission could be fine but the number and the uncertainty could not be evaluated.

Response 1: We agreed with it and improved the expression in section 3.4 and 3.5. However, the spatial distribution of crop residue open burning is very dispersed and the combustion process is rapid, which makes it difficult to monitor its emissions using conventional ground investigation. Most current studies have verified the accuracy of the emission inventories by comparing them with previous studies, and analyzed their uncertainties through Monte Carlo simulations. The uncertainties of the emission inventories of this study are analysed in detail in section 3.4 and 3.6 by comparing the results of previous emission inventories and using Monte Carlo simulations. In addition, the comparative analysis of emission inventories with satellite AOD has been added to section 3.5.

Point 2: The emission coefficiency and the uncertainty of the pollutants from burning crop residue would related to the dryness and compactness of the residue, which should be estimated by either satellite data or ground observation.

Response 2: Thanks for your valuable comments. The physical and chemical properties of crop residue (water content, density, etc.) have an impact on the emission factors of pollutants emitted from the crop residue combustion. Accurate EFS can be obtained from field or laboratory measured, which is difficult to be conduct conducted widely. Emission tests for crop residue open burning in China are relatively few. So, we revised the expression and complemented the uncertainty analysis on emission factors in section 2 and section 4. In section 3.6, uncertainty of emission factors is taken into account when using the Monte Carlo method for the uncertainty analysis of emission inventories.

Point 3: The results of the paper could be compared with other air pollutant data set, such as AOD.

Response 3: Thanks for your valuable comments, we followed your suggestions. We compared the PM_2.5 emission with MAIAC AOD in section 3.5.

Reviewer 2 Report

Li et al. estimated the air pollutant emissions from open burning of crop residue in Hubei Province, China during 2012-2020 based on the satellite data and the relevant data provided by previous studies. The authors showed the emission amounts of different air pollutants from 2012 to 2020 and analyzed the uncertainties. I feel that the manuscript fits the scope of remote sensing and could be accepted after minor revisions.

Specific comments:

1. Do the spatial distributions of fire in Hubei Province vary significantly in different years? When the authors calculated the OBP, they used the total fire amounts in Hubei to get the OBP in other years, which meant that the OBP was spatially consistent in one year. For example, if the authors calculated the ratio of fire amounts in each grid in 2013 to 2012, I am not sure if the spatial distribution of the ratio had great variations. If so, the authors should calculate the grid-level OBP in other years.

2. Was the crop production from the Hubei Statistical Yearbook city-level, or county-level, or province-level?

3. Table 1. Are there any reasons for the authors to choose the grain-to-straw ratio? I saw that the grain-to-straw ratio in Peng et al. (the No.21 reference in the manuscript) was different from the ratio in Table 1.

4. The authors should introduce the Monto Carlo method for uncertainty analysis in Section 2 briefly.

5. Line 81, ‘There is a large amount of crop residue will be burned after harvest each year.’ should be revised as ‘a large amount of crop residue will be burned after harvest each year’

6. Line 110-111. Please use the same unit for ‘27,274 Gg’ and ‘25 billion kg’

7. Line 154, ‘conduct’ should be ‘conducted’.

Author Response

#Reviewer 2:

Response: Thanks for your constructive suggestions. We have made a major revision according to your comments.

Point 1: Do the spatial distributions of fire in Hubei Province vary significantly in different years? When the authors calculated the OBP, they used the total fire amounts in Hubei to get the OBP in other years, which meant that the OBP was spatially consistent in one year. For example, if the authors calculated the ratio of fire amounts in each grid in 2013 to 2012, I am not sure if the spatial distribution of the ratio had great variations. If so, the authors should calculate the grid-level OBP in other years.

Response 1: Yes, the spatial distribution of fire in Hubei Province vary significantly in different years. Therefore, in section 2.3, we used the number of annually fire points in each grid as a spatial proxy to spatially allocate the total emissions per year. The CO₂ emission in Figure 5 show a reasonable spatial distribution of emissions inventory over different years. We modified the express in section 2.3.

Point 2: Was the crop production from the Hubei Statistical Yearbook city-level, or county-level, or province-level?

Response 2: The crop production from the Hubei Statistical Yearbook city-level.

Point 3: Table 1. Are there any reasons for the authors to choose the grain-to-straw ratio? I saw that the grain-to-straw ratio in Peng et al. (the No.21 reference in the manuscript) was different from the ratio in Table 1.

Response 3: The grain-to-straw ratios in this study were based on literature survey and follows several principles: first of all, the latest measured grain-to-straw ratios of different crop species in Hubei Province are preferred. When the grain-to-straw ratios in Hubei Province were not available, we used the research results from domestic measurements.

Point 4: The authors should introduce the Monto Carlo method for uncertainty analysis in Section 2 briefly.

Response 4: Thanks, added.

Point 5: Line 81, ‘There is a large amount of crop residue will be burned after harvest each year.’ should be revised as ‘a large amount of crop residue will be burned after harvest each year’.

Response 5: We followed your suggestion.

Point 6: Line 110-111. Please use the same unit for ‘27,274 Gg’ and ‘25 billion kg’.

Response 6: Sorry for the negligence, changed.

Point 7: Line 154, ‘conduct’ should be ‘conducted’.

Response 7: Fixed.

Reviewer 3 Report

This work proposed a new method to improve emission inventories for emissions from crop residue open burning. Such inventories are very important to improve air quality and to see if new policies are effective. The paper is well written, but before the paper is published, I would like that the authors could addressed the following questions and comments:

- In the introduction it would be recommended to introduce a table summarizing previous studies and main characteristics of these studies, instead of only describing it as text.

- This same table could be useful for discussion of the new estimates of emissions with previous ones done in these studies.

- If there is fire of other type during the studied period, how can these be dealt in the analysis to separate the emissions of such fire from crop residue open burning?

- It would be desirable that in the discussion the authors could explain if the method developed in this paper could be applied to other regions of the globe and which changes would be required in the methodology to do that.

- How uncertainties in the amount of different types of crops and their production, Grain-to-straw ratio and combustion efficiency can affect the results of this study? Have they done a sensitivity study about that? It would be desirable that the authors could identify the main uncertainty source in their study.

- Please change "3.4. Comparison with others " by "3.4. Comparison with previous studies"

- Please change: "The emission inventories in Hubei were compared in detail with previous researches" by "The emission inventories in Hubei were compared in detail with previous studies commented in introduction".

Author Response

#Reviewer 3:

Point 1: In the introduction it would be recommended to introduce a table summarizing previous studies and main characteristics of these studies, instead of only describing it as text.

Response 1: We followed your suggestions.

Point 2: This same table could be useful for discussion of the new estimates of emissions with previous ones done in these studies.

Response 2: Thanks, added.

Point 3: If there is fire of other type during the studied period, how can these be dealt in the analysis to separate the emissions of such fire from crop residue open burning?

Response 3: First of all, we used the land cover data to distinguish between different types of fire points, and identified the thermal anomaly points on the farmland as crop residue burning fire points. In order to ensure the accuracy of agricultural fire identification, high-resolution remote sensing images are further used to remove noise points through visual interpretation.

Point 4: It would be desirable that in the discussion the authors could explain if the method developed in this paper could be applied to other regions of the globe and which changes would be required in the methodology to do that.

Response 4: Thanks for your valuable comments, we followed your suggestions.

Point 5: How uncertainties in the amount of different types of crops and their production, Grain-to-straw ratio and combustion efficiency can affect the results of this study? Have they done a sensitivity study about that? It would be desirable that the authors could identify the main uncertainty source in their study.

Response 5: Thanks for your valuable comments. We introduce the method of uncertainty analysis in Section 2.

Point 6: Please change "3.4. Comparison with others " by "3.4. Comparison with previous studies".

Response 6: Thanks, changed.

Point 7: Please change: "The emission inventories in Hubei were compared in detail with previous researches" by "The emission inventories in Hubei were compared in detail with previous studies commented in introduction".

Response 7: Changed.