Long-Term Trend of the Levels of Ambient Air Pollutants of a Megacity and a Background Area in Korea
Yi Lu
Round 1
Reviewer 1 Report
The objective of the paper is
- to analyse the trends in air pollution at two monitoring stations, one in an urban area (in Seoul) and one in a remote area (Baengnyeong Island) from 2012 to 2019.
- to explain the trends by the emission changes in the area.
To address the first objective, the authors analysed the data measured at the monitoring stations using standard statistical methods and programs.
For adressing the second objective, the authors reported SO2 emission data for China (aggregated) and some South Korean regions.
With these data the authors than confirm an earlier study (cited as Zheng et al.) explaining qualitatively that a reduction of SO2-emissions leads to a decrease of SO42- concentrations, while NO3- tends to increase. A further conclusion is, that in Seoul SO2 concentrations are reduced less than in Baengnyeong Island as around Seoul SO2 sources are operating.
The author cite another study (Uno et al, 2020), where these findings are explained by the high and more or less constant emissions of NH3.
The statistical analysis is correct and the findings are valid. However, for someone familiar with some basic knowledge in atmospheric chemistry the findings are trivial – and not new. To develop some new scientific findings, the authors should have used atmospheric models to establish a quanitative relationship between emissions and concentrations – which of course would have involved not only SO2 emissions. An interesting subject might also have been to verify the emissions in North Korea, which could have been deduced with receptor modelling.
Futher remarks:
In Fig. 5 and 6, the bars for the highest PM2.5 concentration class show no black section,, but two green (NH4) sections, this seems to be a mistake.
The determiner ‚the‘ is often missing in the English text, e.g. in the introduction.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
General Comments
The manuscript is well written and shows plaubible and important results.
At some few points I suggest to make minor changes (see below).
Detailed Comments
line 13: I suggest to add a komma after megacity.
line 15: I suggest to rearrange the sentence to 'Long-term chenges ... were analyzed using the Mann-Kendall trend test and .....
line 16: 'According to' can be understood in various ways. Do you mean (i) that changes in pollutants emission and NO3 in fine particles becoming major species are in accordance, i.e. that the two developments correspond? or do you mean (ii) that changes in pollutants emission are the reason for NO3 becoming major species? or do you mean (iii) that pollutants emission are saying that NO3 is the major species? I suggest to use another formulation.
line 62: In these sentences you may emphasis a bit more that these are/were the goals/objectives of the study. You may also think of adapting the wording a bit to point this out. I nice way would be an enumeration or bullet points with the three mentioned goals.
line 74: Maybe change to 'In this study, we analysed the data of measurements from Januar 2012 to December 2019 (8 years) from both stations.
line 79: Maybe add some words on the landscape arount the Baengnyeong Island Monitoring Station too.
line 80: To monitor air from outside you may need to consider the wind direction, e.g. if there is a prevailing wind direction, this may be a reason that the station can be used for this purpose. If so, you may mention it here. Otherwise, wind speed and direction measurement would be necessary to identify from where the measured air probably came from.
line 120: Maybe replace 'time' with 'time period'
line 120: I suggest to replace 'through' with 'with'
line 121: I recommend to replace 'statistical analysis 120 of time series data is possible with the accumulated data' with 'statistical time series analyses method could be applied to the whole data series'
line 121-126: Maye formulate a bit consiser that Mann-Kendall is a trend test and Sen's slope is a slope calculation method.
line 149: consider putting this information in a table
line 177: Explain the symbols in the figure caption too (e.g. red dot).
line 194: Add the unit of the Sen's slope to the table or the figure caption (e.g. mikro g m-3 per hour)
line 194: maybe add a column with the relative change over the whole period (8 years) calculated as relative change = (Sen's slope x period ) / mean value (e.g. of the first year).
line 216: Provide the source fo the data in table 3. If necessary also add a paragraph in the methods section of the manuscript on this.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
This paper analyzed long-term trend of fine particles and gaseous species at Seoul (representative for urban area) and Baengnyeong Island (a background reference location). Mann-Kendall test and Sen’s slope are calculated to reveal the trends of each specific species. Data for other locations like Incheon, Gyeonggi and China, is compared with the results in the current study. Sulfur oxidation ratio (SOR) and nitrogen oxidation ratio (NOR) are calculated so that the fractions of sulfur and nitrogen in the particle phase is estimated. Generally, the paper is well written in terms of structure, the way how the results are shown (tables and illustrations) and thorough discussion. Conclusion is made clearly, also. I only have minor suggestions as follows before I recommend it publishing in Applied Sciences.
- Fig 1 and Fig 2 use boxplot to describe the measured data in Seoul and Baengnyeong island on the major pollutants. In addition to the parameters of the boxplots, I can also see a red circle for each year and it seems that this red circle is not defined in the text. It is good to clarify what these red points stand for.
- In Figure 3, there shows some data which are not measured in the present study. It is suggested to specify the references (where the data is referred from).
- Figure 4, the subnumber (a) is missing.
- Figure 8 caption is wrongly expressed. (a) is for SOR both in Seoul and B Island and (b) is NOR in both places.
- Some grammar errors are found in the text. One example, page 18, line 390, “and NOR increased rapidly than SOR.” lacks a “more”. I didn’t check every single sentence but I suggest the authors do this again in the revised version.
Author Response
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Author Response File: Author Response.pdf
Reviewer 4 Report
The manuscript analyzes the correspondence between data onpollutant emissions and the results of their measurements
in a large urban agglomeration of the Republic of Korea and
on a relatively remote island. Such work is certainly necessary
to confirm the real relationship between emission data and the
observed state of the atmosphere. Note the good choice of
measuring sites.
The report was done at a high scientific level, beautifully
framed and can be published as presented.
Author Response
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Reviewer 5 Report
This study utilized PM2.5 and gaseous pollutant data from two stations in South Korea to investigate the changes in air pollution composition between 2012 to 2019. While the study had valuable data and provided some interesting insights, there are some major concerns that need to be improved before the study is publishable.
Major concerns
- The description of the study method is not complete. For example, the method section did not describe how equivalence ratios were calculated. Also, many important steps of data cleaning and data quality control were not described. What are the percentages of missing values, what methods were used to detect and handle extreme values, and how were values below detection limits were handled?
- The data and findings presented here are insufficient to support the authors' conclusion. The author provided how the proportion of sulfate and nitrate have changed over time and therefore concluded that this change is mainly due to the lower emission of SO2, mainly from China. However, there were several questions unanswered. Why were the trends different between Seoul and Baengnyeong Island? Are there other studies that support how local emission sources shape this trend in Seoul in addition to the SO2 emission data listed here? Does the trend of CO in Seoul indicate any other potential explanations? Also, how was the change in NOx emission in China and in South Korea? In figure 5, it seems that the proportion of ammonium increased most during peak PM2.5 events and how does that interact with nitrate and sulfate (there are some shared emission sources for these three pollutants). All these questions were left unanswered when the authors jump to the conclusion that the change was caused solely by the reduction of SO2 emissions.
- Results were poorly presented. The figures presented in this manuscript often fail to demonstrate the authors' points. Both figure 7 and figure 13 were presenting data in a very confusing way for readers (multiple colors when unnecessary, unclear legends, confusing arrows) and fail to show the main trend that supports the authors' points. Even for other figures (e.g. figures 10 to 12), there is a much more efficient way to show the trend that the author wants to emphasize. I understand that the authors want to provide almost all the information in their figures but that is problematic as it can mask the main trend. I would strongly suggest authors revisit each figure, think of the main trend/point they want to illustrate and redesign the figures to show that one main point.
- Incorrect satistical language. The authors used "significant" in many places in the manuscript when they didn't conduct a statistical analysis to test the significance. Please note that "significant" is attached to a specific statistical term and therefore should not be used this way. I would highly recommend that the team consult a biostatistician before resubmitting this manuscript. It was shown that the authors weren't very clear about how to report the directions and significance of specific statistics.
Minor concerns
- Please unify the fonts and subscript numbers when needed (e.g. PM1).
- The manuscript needs to be edited for English. Several places were unclear due to incorrect language (e.g. line 63-65, 126-127, 168-169)
- Line 82-87, for the Baengnyeong Island, the author claimed that it was mainly influenced by emissions from foreign countries but then included South Korea in the latter statement. I would suggest providing a map for both locations and wind directions to clarify this.
- Line 88, No method was provided for measuring elemental constitutions.
- Line 195 - revised to "OC showed no significant trend during this period". Significance and direction of change are two perspectives of a trend and therefore should not be mixed together in one statement.
- Table 2. Please clarify in your method if Sen's slope is not calculated for any pollutant with a non-significant trend detected in the Mann-Kendall test.
- Line 208-214. Please provide explanations for why the NO2 levels in Baengnyeong Island are increasing which is inconsistent with the trend observed in Souri et al. Satellite data reflect the change in concentration. If you want to conclude that the decrease in your study is from a decrease in emission, you need to provide studies that look at emission inventory.
- Line 237 - Incorrect statement. The SO2 decreased significantly in Seoul based on the trend test but to a smaller scale than the Island.
- Figure 7 - This figure cannot show how the ratio changes over the year. Please use the year as the x-axis and then the ratios between SO42- and NO3- to show the trend over time.
- Line 308- conclusion made here is not supported by the findings above directly.
- Line 338-340 -A larger increase of NOR in high PM2.5 concentration indicate that particles are more aged in high PM2.5 events but do not support that there is a larger contribution from NO3-.
- Figure 13 - This figure is currently not displaying the key messages and presenting data in an efficient and understandable way. Please calculate the ratio and then plot the ratio (y-axis) over time (year as x-axis), remove the arrows.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors answer, that the recommendations raised in my review are addressed in other publications. But what are then the innovative elements (new knowledge) in this paper?
Author Response
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