The Characteristics and Distribution of Chemical Components in Particulate Matter Emissions from Diesel Locomotives

Round 1

Reviewer 1 Report

Manuscript details:
Journal: Atmosphere
Manuscript ID: atmosphere-1010145
Type of manuscript: Article
Title: The Characteristics and Distribution of Chemical Components in Particulate Matter Emissions from Diesel Locomotives to Build an Inventory of 
Non-road Pollutant Sources
Authors: Min-kyeong KIM, Duckshin Park *, Minjeong KIM, Jaeseok Heo, Sechan Park, Hwansoo Chong 

 

This manuscript reports the chemical composition of particulate emissions from diesel locomotives operating at a range of loads, using both a PEMS with inline filter and a gravimetric method. Refining chemically speciated emissions inventories is a valuable research topic. However, the authors focus mostly on mass emissions of TSP using the two methods, while the presentation of the chemical data seems like an afterthought. Given that the PM collected here is not size-segregated, the novelty and importance of this aspect of the paper are overstated, and the authors frequently incorrectly refer to it as “dust” and/or “fine.” The measurements of metals and ions are more novel and should be emphasized more, particularly in relation to operating load, which is not discussed at all for the metals. After MAJOR revisions, particularly fixing inaccurate statements about particle size, this article could be considered for publication.

 

 

Lines 4-5: Remove “to Build an Inventory of Non-road Pollutant Sources” from the title. This is far outside the scope of the authors’ data and is misleading to include in the title.

 

Line 24: As the authors state in the article, “fine” PM refers to particles with aerodynamic diameter of 2.5 µm or less. And dust is a specific type/component of PM, not a synonym for PM. Because the samples discussed here are exhaust emissions of unknown particle size, it is not accurate to call them “fine dust.”

 

Lines 33-34: Remove the last sentence of the abstract (“Reflecting this…”). As noted about for the title, this is outside the scope of this study.

 

Line 40: Fix numbering of sources: these are the first three sources cited, but are numbered 3-5.

 

Line 50: Non-road emissions are 2% of total in Korea? Or diesel locomotive emissions are 2% of non-road?

 

Line 62: Fine PM was defined previously on line 42, no need to repeat it here.

 

Line 66: Change “Dust” to “PM” (see comment on Line 24).

 

Lines 66-68: Needs citation. Ionic content of PM differs spatially and seasonally – is the research cited relevant to diesel PM?

 

Lines 68-69: Is this sentence referring to the previous study, ref. 13, or to the current study in review? If referring to the previous study, clarify that in the sentence. If referring to the current study, “as a function of particle size” is not accurate – there was no size selection during sampling, so particle size is unknown.

 

Lines 70-90: The article would read more clearly if these two paragraphs were switched. The paragraph that is currently lines 70-80 is discussing the current study’s methodology, and is more similar to the last paragraph in the introduction (starting line 91).

 

Line 84: PM2.5? PM10 is the largest size fraction of respirable particles….

 

Lines 90-91: Why compare these two methods, if the PEMS can collect inline filters?

 

Lines 92-94: As noted for lines 68-69, particle size is not measured here, so “as a function of particle size” is incorrect and misleading. Also, I am not sure about the literature available for chemical composition of locomotive diesel emissions specifically, but there has been extensive research on the chemical components of PM emitted from diesel vehicle engines. Explain why the characteristics of these diesel emissions are different (i.e., why vehicle diesel emissions cannot be used as a proxy for locomotive diesel emissions and this study is justified).

 

Line 116: Define “bhp” in table

 

Table 4: Citation(s) needed for emissions data

 

Table 5: Citations needed for this table as well. “During purification…” This sentence is not clear – is it trying to state that sulfur compounds are formed? Or increase/decrease?

 

Line 125: Define SAE. Need citations for these testing procedures

 

Lines 140-141: Not clear – what is the purpose of “an auxiliary smoke chimney in the chimney”?

 

Lines 144-145: Either describe the filter type and collection device here, or wait to discuss filter measurements until section 2.3 where those descriptions are currently.

 

Line 146: Pre-heating to avoid condensation of exhaust gas? Describe this process in more detail: to what temperature and for how long? Was there a validation process to confirm that this is sufficient to prevent condensation?

 

Line 149: “Proves” should be “probes”?

 

Line 151: “rated” should be “rate”. Need more information about flow rates and calibration: at what flow rate was the sampler operated? What type of flow meter was used for calibration purposes, and what was the range of allowed flow rates?

 

Line 154: Temperature was increased for the PEMS? Exhaust gas temperature was higher? (Both?) Please clarify.

 

Lines 156-167: Details about the filters are not clear. Is the filter in the PEMS made of PTFE (line 163) or PTFE-coated (line 156)? Did the gravimetric device use quartz of PTFE 80mm filters, or both? Do the 3 filters collected for each notch refer to triplicate measurements? Were loading blanks collected?

 

Lines 171-172: Need citation.

 

Line 179: Rephrase – “samples were simultaneously injected into anion and cation IC columns”

 

Table 6: Table headers should be “Ion” and “MDL (ppm)” and nitrate is NO₃^-, not NO₃^2-

 

Line 187: Qualitative?

 

Lines 193-195: Why is this sentence included in the methods?

 

Table 7: Same comment as Table 6 about headers

 

Line 206: Typo: TPS should be TSP

 

Line 214: PMES and TPS should be PEMS, TSP

 

Lines 235-236: This sentence should be in the previous paragraph

 

All figures: show uncertainty of replicate measurements

 

Line 244: mass of PM, not dust

 

Line 246: What is the purpose of defining Factor K, since it is not used in any further calculations in the paper?

 

Lines 268-271: Comparing measurement methods is not related to establishing an inventory of non-road emission courses.

 

Figure 5: Keep terminology consistent with Figure 4, or even better, combine these two figures.

 

Lines 276-279: Reminder, again, that dust is just a type or component of PM. Dust cannot be used to describe PM in general. Also, “natural” production of PM is indeed a chemical process. The authors are presumably referring to the anthropogenic and biogenic sources that both contribute to PM.

 

Lines 280-291 and Table 8: Nitrate is NO₃^-, not NO₃^2-

And why present this data in terms of mass per filter? It would be more useful to normalize to PM mass, air volume, and/or fuel consumption. Comparing mass of an ion per filter is completely controlled by how much PM was sampled on the filter. Relative to PM mass, does the ionic composition – the relative amounts of each ion – change between load levels?

 

Lines 292-293: Was carbon content measured in these samples? Also, the fact that ions have been measured in other atmospheric PM is not relevant to these results, and there are several decades of this data available.

 

Line 294: As mentioned several times previously, this study measured TSP, not fine PM

 

Lines 300-302: This sentence contradicts itself – which is the order? Are these ion quantities defined relative to total PM mass, or to fuel consumption? And how do these abundances compare to the data presented here?

 

Lines 319-328: Why were no quantitative elemental data presented, either in tables or figures? This is arguably the most novel component of this data, yet the authors spend little time presenting/discussing it. As with the ions, normalize element concentrations to PM mass and/or fuel consumed, then compare to other diesel emissions data, such as from diesel vehicle engines.

 

Lines 349-351: All data presentation should be in results/discussion, no conclusion – why was this not presented earlier?

 

Lines 355-356: As noted for lines 292-293, ambient PM is not relevant to this study. The better comparison is availability of chemical data for diesel locomotive engines as opposed to other types of diesel engines.

 

Line 444: Ref 32 is a duplicate of 28, and was not actually cited in the manuscript

Author Response

Please see the attachment. 

Author Response File: Author Response.pdf

Reviewer 2 Report

This study analysed the chemical component of diesel locomotives exhaust particulate matter. Diesel exhaust PM is responsible for different respiratory diseases and the precise understanding of the characteristic of diesel exhaust PM is important for health risk assessment of human. Authors used PEMS to measure the particulate matter from the vehicle. The significance of the study is enough to be published in this journal. However, authors must need to improve the following section before the final publication;

1. Abstract is detailed enough and clearly illustrated the significance of the study. However, the major findings of the study are not clear from the abstract. Authors need to include a sentence by mentioning the major findings of the study.
2. The introduction is detailed enough and discussed the health impacts of diesel exhaust PM. In line 46 and 64, authors mentioned about the human health and authors need to cite more relevant paper to support their discussion. Authors need to site the (https://www.nature.com/articles/s41598-019-48753-6) the paper, which analysed the diesel exhaust particle and it’s impact on respiratory health.
3. Table 4, PM10 and PM2.5 emission is mentioned. Is it from one observation or average of multiple observation? Authors need to mention it in the revised manuscript.
4. Table 4, the authors used the last column for total emission. It makes me so confused and is it si important? Authors got emission from different sources and how it will be round 100%. Please discuss it in the revised manuscript.
5. Line 211, authors mentioned the difference between two methods and authors could illustrate the reason behind it.
6. Figure 3(a), concentration for 1 notch is not following the trend and it’s in between two other cases. However, other cases are following the same trend. Authors need to explain it.
7. Figure 3(a), please check the spelling of concentration.
8. Same comment for figure 3(b).
9. Authors may highlight the key findings in the conclusion section and need to write a sentence of how the present study will improve the knowledge of the field.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors addressed most of the minor comments, but did not fully address the major comments. Specifically, although there is somewhat more quantitative chemical data, the units and/or why experiment is referred to are often unclear. This is essential information, but the authors do not seem concerned with presenting their data accurately, which is concerning.

 

10. These were not the paragraphs that I recommended the authors switch. I guess the reasoning behind that suggestion wasn’t clear, so I will try to explain. Usually an introduction starts with background knowledge on the topic, explaining to the reader what is and is not known. Then at the end of the introduction, before describing the research, the novelty of that research is stated. So the paragraph starting with “Atmospheric dust contains…” is background knowledge, while the paragraphs starting with “This is the first report of…” are explaining the novelty of the research presented here, so I suggest putting them at the end of the introduction.

 

41. Why is the chemical data still presented in units of ug/filter? This is a confusing and meaningless unit. If the authors do not want to report data normalized to TSP mass, please provide an explanation to justify that.

 

For the pie charts, exclude the components that have only very small contributions – the very small wedges in the pie chart cannot be distinguished, even with text labels, and having all those labels on the plot makes the labeling of the larges wedges unclear.

 

43. Does “Ionic components accounted for more of the fine PM chemical content than did metal” refer to previous studies? If so, cite. If this is meant to refer to the current study, it is not accurate because the current study only measures TSP, not fine PM.

 

45. The authors still do not present any comparison between the notches they tested. Why not? And for the data that is presented, it is not specific whether that is for a specific notch or for all of them. This must be clarified.

 

Other comments about revised text:

 

Line 316: This study measured TSP, not PM10. So the paper cannot say that they measured PM10.  

 

Line 311: Need citation for statement about large diesel engines and generators

 

Line 372: Need citation for 58%

 

Line 379: Fe is 82% of what? Unclear.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

Authors improved the manuscript based on the reviewer suggestion and replied every points. I am happy with the current version and it can be accepted for publication.

Author Response

Dear. reviewer

Thank you for reviewing my thesis.

I will continue to conduct related research in the future.

Thank you in advance.

Sincerely