Crop Residue Burning in Northeast China and Its Impact on PM_2.5 Concentrations in South Korea

Round 1

Reviewer 1 Report

This paper shows the results obtained with a very ambitious attempt to find a possible cause of an anomalous increase in PM_2.5 in South Korea in the meteorological framework of the region. The attempt does not appear to be successful, although only two extreme events have been analyzed. This is not surprising given the large number of variables that come into play. However, a certain correlation between the increase in PM_2.5 in South Korea and crop residues burning in north-east China appears evident, even if a real traceability is not demonstrated. On the other hand, the conclusions are correct as they  recommend only the inclusion of crop residues burning in north-eastern China among the variables to be considered in future analyzes of PM trends in South Korea.

The text appears well written and the figures and tables well done, even the bibliography is sufficiently extensive. I believe that the paper may be of interest to readers, even if the results are not entirely positive. I believe the article can be published in the present form

Author Response

Thanks for your comment.

Reviewer 2 Report

1. The biggest problem of this paper is, it is using circumstantial evidence rather than direct experiment. CMAQ can simulate the crop burning effect, as demonstrated in Zhou et al. (2018). The observational data can be a piece of good supporting evidence. However, correlation does not imply causation. (As in line 222, the authors do not feel confident, and have to use the word "likely") So the author should consider adding one essential experiment, in which the CMAQ simulates the crop burning effect directly.
   • Zhou, Luxi, et al. "Modeling crop residue burning experiments to evaluate smoke emissions and plume transport." Science of The Total Environment 627 (2018): 523-533.
2. This study does not give a clear validation of the meteorology fields. Therefore, we can not exclude the potential that the underestimated PM25 is due to a low performance from WRF.  
3. It appears to be problematic to have the same physical configurations for both coarse and fine grids. In particular, for cumulus parameterization, it might not be the optimal choice to use KF for the 9km grid.
4. The CO2 from crop burning is another major pollutant, as described in Sun et al. (2013). Did you observe a similar signal in your study?
   • Sun, Jianfeng, et al. "An estimation of CO2 emission via agricultural crop residue open field burning in China from 1996 to 2013." Journal of Cleaner Production 112 (2016): 2625-2631.
5. In addition, this paper only studied two cases, which are too few to get a statically sound conclusion. Furthermore, crop burning can happen in other seasons, particularly in summer might have more burning activities. Therefore additional simulations should be conducted.

Author Response

Thanks for your comment.

1.  CMAQ can simulate the crop burning effect, as demonstrated in Zhou et al. (2018). The observational data can be a piece of good supporting evidence. However, correlation does not imply causation. (As in line 222, the authors do not feel confident, and have to use the word "likely") So the author should consider adding one essential experiment, in which the CMAQ simulates the crop burning effect directly. Zhou, Luxi, et al. "Modeling crop residue burning experiments to evaluate smoke emissions and plume transport." Science of The Total Environment 627 (2018): 523-533.

--> Zhou et al (2018) estimated emissions of crop residue burning based on available field information. However, it was impossible to obtain available field information for estimating used in the study of Zhou et al (2018). Therefore, we couldn’t conduct the air quality modeling using emissions of crop residue burning for the case 2. We described these limitations in the conclusion as follows: This study has a limitation that the air quality modeling could not be performed using the emissions of crop residue burning in northeast China because it was not possible to obtain the available emission information (location, field size, fuel load, etc.) for estimating them.

2. This study does not give a clear validation of the meteorology fields. Therefore, we cannot exclude the potential that the underestimated PM₅ is due to a low performance from WRF.

 --> Figure 4 as revised by adding weather charts provided by the Korea Meteorological Administration (KMA) to evaluate the performance of the WRF simulations. Figure 4 showed that the simulated wind field is consistent with the atmospheric pressure patterns shown in the weather charts. Therefore, the simulated wind field, which is an important factor for PM₅ transport, is generally evaluated to be good.

3. The CO₂ from crop burning is another major pollutant, as described in Sun et al. (2013). Did you observe a similar signal in your study? Sun, Jian Feng, et al. "An estimation of CO₂ emission via agricultural crop residue open field burning in China from 1996 to 2013." Journal of Cleaner Production 112 (2016): 2625-2631.

 --> As the mentioned in Q1, we didn’t directly estimate emissions of crop residue burning for the case 2 in this study. We couldn’t check the signal of CO₂.

4. In addition, this paper only studied two cases, which are too few to get a statically sound conclusion.

 --> We agree with your opinion which two cases are too few. Additional studies are necessary to verify our results using more cases. But, the main purpose of this study is to understand the characteristics of different phenomena. Therefore, we think that the analysis of two cases is sufficient to achieve the purpose of this study.

Reviewer 3 Report

The paper “Crop Residue Burning in Northeast China and Its Impact on PM2.5 Concentrations in South Korea” deals with a timely subject.

I have the following comments:
•    Provide practical significance of the results obtained in the study. 
•    Could the authors define some practical suggestions based on the outcome revealed from the study? 
•    What measures should be taken to lowering in Case 2.
•    The novelty and contribution of the paper should be briefly clarified.
•    Nomenclature section is missing,

I suggest accepting the paper if the authors succeed in addressing these comments.

Author Response

Thanks for your comment.

1. Could the authors define some practical suggestions based on the outcome revealed from the study?

 --> This study showed the forecast system failed to predict high concentrations due to a lack of input regarding crop residue burning in northeast China. Therefore, the practical suggestions is as follows; the performance of AQM should be improved via the inclusion of air quality data assimilation of satellite and ground data to consider the occurrences of irregular periodicity such as crop residue burning.

2. What measures should be taken to lowering in Case 2.

 --> The measures to lowering PM_2.5 concentration are to reduce emissions in source regions. So, Along with strengthening the crackdown on reducing crop residues, a system is needed to deal with them at incineration facilities after collection of crop residues.

3. The novelty and contribution of the paper should be briefly clarified.

 --> The results of this study can be used as scientific evidences to plan the policies for improving air quality. Particularly, the policies that are going to be enacted in the future aimed at improving South Korean air quality should consider crop residue burning in northeast China.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Other parts are good, but the reply to the first comment is not acceptable. Zhou offered two treatments for how to obtain cropland fire emissions information, the authors should have sufficient information to conduct a similar experiment. EPA data is publicly available. Even an idealized experiment is better than nothing. I would hold my opinion until the author provides the additional experiment as suggested.