Atmospheric Oxidation Capacity and Its Impact on the Secondary Inorganic Components of PM_2.5 in Recent Years in Beijing: Enlightenment for PM_2.5 Pollution Control in the Future

Round 1

Reviewer 1 Report (Previous Reviewer 1)

No further comments since I revised already

Author Response

-

Reviewer 2 Report (Previous Reviewer 2)

The authors have done a large job and corrected most of the remarks. It’s quite pity that they couldn’t provide analyses of meteorological characteristics that, to my opinion, would imply the conclusions. Nevertheless, I do not object to the publication of this article in the current form after making some minor corrections and checking the conclusions which are still partly doubtful.

Remarks

Lines 24-27 – In current view this sentence is not correct because in its first part yearly Ox concentrations are meant. So the sentence has to be redone

Line 142-143 – NO is unstable gas and can hardly be used for calibration. The statement itself is quite obvious. Specifications of gas standards (at least name of manufacturer and accuracy) are needed to make sense of this sentence

Line 419 — It says «sulphur» here while in other chapters of the paper «sulfur» is used. This should be unified

Line 452-457 — This statement seems to me doubtful as the exponential function roughly describes the dependency and value 140 μg/m3 cannot be considered a threshold. What is the statistical meaning of the fits? The conclusion about 140 μg/m3 should be at least relieved.

Fig. 11 — Differences in r² values on left and right plots are surprising while the scatter of values is similarly large on both plots. This fits should be checked.

Line 461 — As I can see this fit is non-linear

Lines 483-487 — see the remark for lines 452-457

Author Response

Minor Comments 1:

Lines 24-27 – In current view this sentence is not correct because in its first part yearly Ox concentrations are meant. So the sentence has to be redone

---Response:

According to the suggestion of the reviewer, we have revised the original sentence to be “The results showed that O_X concentrations reached their peak in 2016 and reached their lowest point in 2019. The concentrations followed a descending seasonal trend of summer, spring, autumn, and winter, and a spatial descending trend from urban stations to suburban stations and back-ground stations.” in the revised version of the manuscript (Line 24-27).

Minor Comments 3:

Line 142-143 – NO is unstable gas and can hardly be used for calibration. The statement itself is quite obvious. Specifications of gas standards (at least name of manufacturer and accuracy) are needed to make sense of this sentence

---Response:

According to the suggestion of the reviewer, we have added information about standard gas in the revised version of the manuscript (Line 143-149).

Minor Comments 4:

Line 419 — It says «sulphur» here while in other chapters of the paper «sulfur» is used. This should be unified

---Response:

Thanks to the reviewer's advice, we will unify this word to sulfur in the revised version of the manuscript (Line 424).

Minor Comments 5:

Line 452-457 — This statement seems to me doubtful as the exponential function roughly describes the dependency and value 140 μg/m³ cannot be considered a threshold. What is the statistical meaning of the fits? The conclusion about 140 μg/m³ should be at least relieved.

---Response:

Thanks for the reviewer's suggestion, 140 μg/m³ is only a rough number, and we only want to describe the change of SOR and NOR with the change trend of OX after a certain value is exceeded. For the sake of rigor, we have refined the original representation by adding around in front of the “140 μg/m³” to indicate that this is a rough number in the revised version of the manuscript (Line 463; Line 465).

Minor Comments 6:

Fig. 11 — Differences in r² values on left and right plots are surprising while the scatter of values is similarly large on both plots. This fits should be checked.

---Response:

Thanks for the reviewer's suggestion, after examining the calculation process, we did not find any problems. We think it was due to the fact that NOR is more susceptible to environmental factors than SOR, resulting in a poor fit to O_X. We add to this in the revised version of the manuscript (Line 452-456).

Minor Comments 7:

Line 461 — As I can see this fit is non-linear

---Response:

Thanks for the reviewer's suggestion, there is indeed an error here, we have changed the “linear fitting” to “exponential fitting” in the revised version of the manuscript (Line 471).

Minor Comments 8:

Lines 483-487 — see the remark for lines 452-457

---Response:

Thanks for the reviewer's suggestion, we have made the same modification as Minor Comments 5 in the revised version of the manuscript (Line 494; Line 496).

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Minor corrections:

The title is too long. I got confused reading it.

Abstract

Sentences way too long. English language is usually made up of shorter sentences.

Line 26-27: The results showed that the concentrations of Ox showed a …   (poor English)

 Line 53. “but there is still a big gap with the WHO guideline value”   à but there is still a long way before reaching the WHO guideline value

Introduction

Author should define what secondary components in PM2.5 means exactly (provide a clear definition somewhere in the intro).

 Eq.1, 2 3. What does subscripts p,h means ? Should define it here, not later. It is only later in the text that I realized that p means primary

 

Line 144 were collected in the daytime (7:30-19:00) and night 144 (19:30-7:00) by off-line sampling method-à what happens between 7:00-7h30, 19h00-19h30  why a gap ? Calibration, data rejected ?

Fig 10. A better fit is probably non-linear. A linear fit is misleading. It would be surprising that the chemical soup would show linear behavior. I suggest trying polynomial fitting (left panel) and exponential fitting (right panel). Try Box-Cox transformation of data and redo the curve fitting.

 

 

Reviewer 2 Report

The Manuscript concerns very interesting topic of atmospheric oxidation (AOC) capacity influence on PM2,5 concentration and secondary aerosols. It is really important task that has not been studied sufficiently so far. Authors use comprehensive set of experimental data including main atmospheric pollutants dataset from observational network in Beijing and data of aerosols ionic composition. The MS contains interesting conclusions about AOC inter-annual and seasonal variations and its relation to aerosol pollution. I would like the paper to be finally published despite it contains significant shortcomings and raises questions indicated below

Remarks:

Lines 25-26 – the descend of Ox can hardly be considered as trend because only 4 years (2016-2019) were considered and only during 2019 for some reason substantial decrease of Ox occurred.

Line 35 – “Sulfur” should with small letter

Line 76 – should be “facing”

Figure 1 – it is unclear where is Beijing. Does it include the whole marked area? If it is so, it should be pointed out that inner lines are borders between city districts

Line 113-114 – it is better to say “The water-soluble inorganic ion components in PM2.5 were also analyzed” or something like that

1.1.3. Source of meteorological parameters (line 115) – I didn’t find in the paper where meteorological data was used. But they should be used at least to determine the reason why concentrations of main pollutants and Ox were declining in 2019

Line 125 - “PM 2.5 was observed online” – what does it mean? Later it is stated that “And PM10 and PM2.5 were monitored using the monitor 5030”. If the same thing is meant first sentence should be omitted. If not, more detailed explanation is needed. By the way, “And” in the beginning of this sentence should be omitted either.

Line 144 - should be “collected in”

Section 1.3.1 – what does it mean “regularly”? More accurate information is needed hear. If this regularity corresponds to some standard it should be pointed out. More information is needed about standard gases (at least manufacturer and accuracy). To add calibration plots at least as a supplementary materials is very desirable.

Line 202-203 – I guess this statement is evident and can be omitted

Formulas 1-3 – what mean p and h? And what mean (PM2.5) and CO? Concentrations? In which units? This should be described in explanations to these formulas

In general, usage of formulas 1-3 causes questions:

- how universal are these empirical formulas? In other words, can they be applied for every city?

- these formulas appeared in paper (S.-C. Chang, C.-T. Lee / Atmospheric Environment 41, 2007) considering air pollution and photochemical processes in Taipei for 1994-2003. Since that time the structure of emissions has been altered substantially. So how applicable will be this approach for Beijing in 2016-2019?

- how justified is the application of same formulas for PM10 and PM2,5 as, for instance, PM10 has higher dependence on coarse particles of mineral origin that is not related to CO.

Line 210 – first CO should be in italic

Figure 2 – to say about trend from 2016 to 2019 a plot based at least on monthly averaged values should be added

Line 277 - “the NO2/OX ratio was higher (0.36)” – higher comparing to what? Actually, if Ox=O3+NO2 and O3/Ox+NO2/Ox=1, no need to mention both ratios in 1 sentence.

Line 331 – If there are both PM2,5 and PM10 apparently PM2,5 should be taken for secondary aerosols analyses.

Line 334 – must be dot instead of comma after “respectively”.

Figure 8 – Concentrations of F- and Mg2+ are too small to see the difference between summer and winter. Maybe interrupted or logarithmic scale is needed for this figure.

Line 472 - “In 2019, the annual mean of OX at all stations in Beijing showed a significant decline” – the reason of that is not explained. It is supposed that improvement of air quality in 2019 was due to emissions reducing or something like that. But first of all, meteorology in 2016-2018 and 2019 should be compared,

References are written carelessly. Sometimes DOI is indicated, sometimes – not. Sometimes it’s given as hyperlink, sometimes – like plain text.