First long-term and near real-time measurement of trace elements in China's urban atmosphere: temporal variability, source apportionment and precipitation effect

Chang, Yunhua; Huang, Kan; Xie, Mingjie; Deng, Congrui; Zou, Zhong; Liu, Shoudong; Zhang, Yanlin

doi:https://doi.org/10.5194/acp-18-11793-2018

Articles | Volume 18, issue 16

https://doi.org/10.5194/acp-18-11793-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-18-11793-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 18, issue 16

Research article

|

20 Aug 2018

Research article |

| 20 Aug 2018

First long-term and near real-time measurement of trace elements in China's urban atmosphere: temporal variability, source apportionment and precipitation effect

Yunhua Chang, Kan Huang, Mingjie Xie, Congrui Deng, Zhong Zou, Shoudong Liu, and Yanlin Zhang

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Final revised paper (published on 20 Aug 2018)
Supplement to the final revised paper
Preprint (discussion started on 01 Aug 2017)
Supplement to the preprint

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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- Supplement

RC1: 'Anonymous referee #1', Anonymous Referee #1, 03 Aug 2017
- AC1: 'letter to reply to reviewers', Yunhua Chang, 30 Nov 2017
RC2: 'Comments on Chang et al.', Anonymous Referee #2, 27 Aug 2017
- AC1: 'letter to reply to reviewers', Yunhua Chang, 30 Nov 2017
RC3: 'referees's comments', Tony Dore, 29 Aug 2017
- AC1: 'letter to reply to reviewers', Yunhua Chang, 30 Nov 2017
RC4: 'referee's comments', Anonymous Referee #5, 03 Sep 2017
- AC1: 'letter to reply to reviewers', Yunhua Chang, 30 Nov 2017

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Yunhua Chang on behalf of the Authors (30 Nov 2017) Author's response Manuscript

ED: Reconsider after major revisions (17 Dec 2017) by Willy Maenhaut

The authors should have addressed the comments of the referees in a better way. Their reply to the second specific comment of Anonymous Referee #1 (with regard to the precipitation) makes in my opinion no sense. The approach that was used to handle this comment is much too simplistic. It is impossible that the atmospheric concentrations of elements such as V, Ni and Si are not influenced by wet scavenging.

Overall, the current version of this manuscript still has serious shortcomings.
1. Although the language and grammar of the manuscript are reasonable, there is still a lot of room for improvement. Several alterations are suggested under "Further comments" below.
2. The authors followed up on the suggestion of Anonymous Referee #2 to replace the word "elements" in the title by "metals". I disapprove of this change. Three of the 18 elements measured (i.e., Si, As and Se) are not metals. Si and As are metalloids and the nonmetal Se is also sometimes considered a metalloid. Also throughout the text "metal(s)" is often used where it should be "element(s)".
3. I agree with Anonymous Referee #5 where he states that the results of the principal component analysis and also the hierarchical clustering do not bring many new insights. Still there are many sentences in the revised manuscript devoted to the results of those two approaches. It is unclear to me why did the authors did not make use of Positive Matrix Factorization (PMF) for source identification and apportionment.
4. The concentration data in lines 28-31 and in lines 316-319 (and on some other occasions in the manuscript) contain too many significant figures. Two significant figures suffice in case the first significant figure is larger or equal than 2, and when the first significant figure equals 1, three significant figures can be used.
5. Section 2.2.1: I presume that hourly concentration data were used in the statistical analyses. If so, this should clearly be indicated.
6. Lines 479-480: Considering that up to nearly 9000 data points were available for each element (if hourly concentration data were used in the statistical analyses), how can the authors make the statement that "much larger datasets are required for definitive source apportionment with PCA"? Even in case daily averages were used in the PCA, then there would still be sufficient data for an appropriate PCA.

Further comments for the Main text:
Lines 26 and 126: What is meant by "reactive filter"? In line 193 it is mentioned that a Teflon filter tape was used in the Xact instrument. Teflon filters are typically not reactive at all.
Line 34: Replace "with other" by "with that in other".
Line 35: Replace "in sites" by "at sites".
Line 44: Replace "sourced from" by "derived from".
Line 213: Replace "at PMC" by "at the PMC".
Line 226: Replace "for species of" by "for".
Line 228: Replace "than other" by "than those of other".
Line 248: Replace "principle component" by "principal component".
Line 257: The acronym "PCA" was already defined in line 248. Its should not be defined again.
Line 303: Replace "has described" by "has been described".
Line 305: Replace "3 Results" by "3. Results".
Line 310: Replace "illustrated in" by "presented in".
Line 334: Replace "accounting for" by "accounts for".
Line 356: Replace "willalso" by "will also".
Line 363: Replace "were also illustrated in" by "are shown in".
Line 378: Replace "winter were" by "winter is".
Line 383: Replace "later)" by "below)".
Line 387: Why is reference made here to the wind speed? There is no information about the wind speed in Fig. 6c.
Line 394: Replace "can be served" by "can serve".
Line 400: Replace "well as" by "well as for".
Line 402: Replace "evening" by "in the evening".
Line 414: Replace "from other" by "from that of other".
Line 415: Replace "and 16:00" by "and at 16:00".
Line 416: Replace "were primarily" by "are primarily".
Line 417: Replace "were more" by "are more".
Line 421: Replace "matters" by "matter".
Line 439: Replace "be primarily sourced" by "primarily originate".
Line 441: Replace "of Cu origins" by "of the Cu origin".
Line 454: Replace "and presented" by "and they are presented".
Lines 456-457: Replace "trace crustal matters" by "crustal matter".
Line 458: Replace "trace crustal matters" by "the crustal matter trace elements".
Line 461: Replace "trace crustal matters" by "crustal matter elements".
Lines 471-473: There is something wrong with the wind directions given here. It seems to me that "west" in line 471 should be replaced by "east" and "southwest" in line 473 by "southeast".
Line 473: Replace "are sourced from " by "originated from".
Line 478: Replace "Explore and constrain more" by "Exploration and constraining of more".
Line 489: Replace "later)" by "below)".
Line 490: Replace "Matrix reorder" by "Matrix reordering".
Line 505: Replace "illustrated in" by "presented in".
Line 511: Replace "Even though" by "Nevertheless".
Line 517: Replace "illustrated in" by "shown in".
Line 529: It is unclear to me what is meant by "reaming".
Line 552: Replace "matters from" by "matter from".
Line 554: Replace "be sourced from" by "originate from".
Line 560: Replace "principle source" by "principal source".
Lines 573-574: Replace "approximately 20 km apart" by "at approximately 20 km".
Line 575: Replace "also evidently reflects" by "also indicates".
Line 597: Replace "e.g." by "i.e.".
Line 624: Insert ", Edinburgh, United Kingdom," after "Hydrology".
Lines 648-658: "Carslaw and Ropkins, 2012" should come before "Carslaw et al., 2006".
Line 844: Replace "Inventory" by "inventory".
Line 1001: Replace "A collection of" by "Overview of".
Line 1008: Replace "although a huge" by "a huge" and replace "had been" by "has been".
Line 1009: Replace "in which no" by "but that no".
Line 1017: Replace "A land use" by "Land use".
Page 34, Figure 2: The unit for the abscissa data ("value") in the right part of the figure should be specified.
Line 1034: Replace "A quick glance of the mass" by "Average mass".
Page 37, Figure 5d: Replace "weakday" by "weekday" in the abscissa.
Page 38, caption of Figure 6, line 2: There is no information about the wind direction in the Figure.
Page 44, Figure 12: The unit for the data in the abscissas and ordinates should be specified. The data in several cells for V, Ni, Ag and Cd are not readable, although for some of them a significance level of "***" is specified. Then, in the last line of the figure caption, 6 p-values are given and only 5 symbols; besides, it is unclear what the last of these 5 symbols really is.
Page 46, Figure 14: It should be indicated that this figure shows component loadings. Furthermore, in the caption of the figure "Principle component" should be replaced by "Principal component".
Page 48, Figure 16: The unit for the concentration data in this figure should be specified.

Comment for the Supplement:
Caption of Table S1: Replace "Inter-comparison of trace metals" by "Inter-comparison between ICP-MS and Xact for trace elements".

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AR by Yunhua Chang on behalf of the Authors (10 Mar 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (13 Mar 2018) by Willy Maenhaut

RR by Anonymous Referee #1 (15 Mar 2018)

Suggestions for revision or reasons for rejection

General comments

The manuscript has been significantly altered by basically replacing the hierarchical clustering method by Positive Matrix Factorization (PMF), and by adding information on precipitation effects on metals concentrations. PMF yields 5 emission sources for Shanghai which are well explained by the measured elemental data, and the high time resolution allows for a strong argument for a traffic-related factor. Precipitation effects do show a general trend in reducing the elemental concentrations, however the picture is complicated by other effects playing a role, such as wind/air mass changes.
There are still a few minor changes required before the paper can be published.

Specific comments

The comparison between filters and Xact has been extended in Table S1, but the description (lines 234-239) is not consistent with the new data. The background values have been dropped from the table, as well as the comparison between the filter types. The quoted values on line 237 refer to the very first version of the table. This should be updated. I still do not buy the explanation of the Cr and Ba slopes depending on the background values. If the background values in the original version of Table S1 were correct, than all cellulose acetate filter background values were smaller than the glass filter background values, in contradiction to the statement. Perhaps the authors leave out that part of the sentence (lines 238-239). Table S1 needs more information in the caption, e.g. explain the asterisks (*, **) and the n values.
In Section 2.1.1. only winter is described. I recommend to add the sequence from the first revision (with my additions):
“Winters are chilly and damp, with northwesterly winds from Siberia sometimes causing nighttime temperatures to drop below freezing. In summer, airflow carries moist air from the Pacific Ocean to mainland China, which will also bring the main precipitation. The city is also susceptible to typhoons in summer and the beginning of autumn.”

Technical corrections
Table 1, L376, L377 make city names consistent
L572 Fig. S14 (not S13)

In supplement
Table S1: explain ‘n’ and the asterisks in the table
Table S2: Replace ‘Text’ with ‘Table’, and insert ‘events ‘ after ‘precipitation’
Caption of Fig. S10: L3 delete ‘of the diagonal’

Hide

RR by Anonymous Referee #6 (13 Apr 2018)

Suggestions for revision or reasons for rejection

The paper “First long-term and near real-time measurement of trace elements in China’s urban atmosphere: temporal variability, source apportionment, and precipitation effect” is based on a huge and interesting data set. Nevertheless, the paper still includes some points that need revision.
Briefly, here is a list of the issues that authors should address for the publication of the paper:
- To the best of my knowledge, Xact can also quantify Al, S, Cl, and Ti: why were these elements not taken into account?
- Still on Xact: what do you mean with “reactive filter tapes” (line 128)? Referees had already asked this question.
- There is quite some confusion between V/Ni and Ni/V ratios: please report only V/Ni ratio values, as this is the main way to report these data. Please revise the abstract (line 41) and figure 6.
- Lines 347-352: the issue of oxides versus reconstructed mass is addressed in a quite simplistic way: could the authors explain the formulas they used for the calculation of the oxides and, mainly, how was the data for total PM2.5 mass obtained? The cited reference helps under the methodological point of view, but it would be helpful to know some more specific details (how did the authors calculate EC/OC, sulphate, nitrate etc. for the reconstruction of the mass).
- Line 450: which is the V/Ni value of the PMF factor? The factor is obviously characterized by the same ratio throughout the year; there is an unclear mix among PMF factor data and raw chemical data.
- Figure 7, CPF and BPP analysis: I suggest the authors to correlate wind data with the factors/sources, while they did it with elements. This would give more powerful information on sources, even thought a single element could have contributions from different sources.
- Section 3.3, “Precipitation effect”. The topic is interesting, but authors should comment their results somehow more critically: e.g., how do they explain the fact that Au and Cr increase during the rainfall? I find this result quite strange... Further, no comment is given on the ferrous metal smelting pattern (fig. 11 e). Last, comparing the effect of a rainfall to the expected one for street-washing appear quite simplistic, as in the first case the whole “air column” is washed, while with street washing only the street surface is cleaned.
- Line 555: in the reference list one more paper by Karanasiou et al. is reported (published in 2011).
- Supplementary material, table S1. Actually, the inter-comparison between ICP-MS and Xact gives not excellent results for some elements (e.g., As, Cd, Ba, Pb, for which a slope of roughly 2 is observed): this issue should be discussed in more detail. Further, with respect to Fe: could the authors check the regression lines? I find strange that the intercept for all glass filters and all cellulose filters are negative but, then, the intercept for all the filters is positive. Last, what do “*” and “**” stand for?
- Supplementary material, figure S4. Wind directions are not reported: please add the panel or change the caption.

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ED: Publish subject to minor revisions (review by editor) (14 May 2018) by Willy Maenhaut

The manuscript has been substantially improved with the PMF results. The aspect of precipitation scavenging is also presented in a better way, but there are still problems with it as indicated in the report of Anonymous Referee #6. The comments and corrections of both Anonymous Referees need to be fully addressed. I also have several comments and corrections, which are listed below, and need to be taken into consideration. Consequently, substantial revision is still needed before this manuscript can be accepted for publication in ACP.

Main comments for the Main text:
1. The language and grammar of the manuscript are fair, but there is very much room for improvement. Many alterations are suggested under "Further comments" below.
2. Line 41: The ratio of 0.31 is too low for a V/Ni ratio in shipping emissions. Does the 0.31 perhaps indicate the Ni/V ratio? If so, replace it by the V/Ni ratio. See also the comment of Anonymous Referee #6 on this topic.
3. Lines 215-216: Since the Micromatter standards were used for calibration, it is unclear to me how one can then derive independent measured and standard masses from them.
4. Line 248: Abbreviations and acronyms (here "USEPA" and "QA/QC") should be defined (written full-out) when first used. Since the acronyms are only used here, "USEPA" can simply be replaced by "United States Environmental Protection Agency" and "QA/QC" by "Quality Assurance / Quality Control".
5. Line 249: It is unclear what is meant by "upscale values".
6. Line 269: The phrasing of "with all elements missed" is somewhat unclear. I suggest to replace "with all elements missed" by "with missing data".
7. Page 13, within Figure 2 (and on various other occasions in the manuscript, e.g., in Table 1, data for this study; in line 334; within Figure 4; in line 408; in line 426): The concentration data contain too many significant figures. Two significant figures suffice in case the first significant figure is larger or equal than 2, and when the first significant figure equals 1, three significant figures can be used.
8. Page 20, Figure 6: Please, replace this figure by one with V in the ordinate and Ni in the abscissa, and provide thus regression lines with V in the y-axis. See also the comment of Anonymous Referee #6 on this topic.
9. Lines 492-494: Literature references are needed for the statements in these two sentences.
10. There are several problems with the References.
The following references to which is referred within the text are not in the Reference list:
Line 256: Paatero and Tapper, 1994.
Line 271: Kim et al., 2005; Kim and Hopke, 2007.
Lines 278-279: Norris et al., 2014.
Line 279: Brown et al., 2015; Paatero et al., 2014; Wang et al., 2017.
Line 414: Hjortenkrans et al., 2007.
Line 416: Thorpe et al., 2008.
Line 435: Chang et al., 2016a. Should the "2016a" perhaps be replaced by "2016"?
Line 520: Wang et al., 2013. There are "Wang et al., 2013a" and "Wang et al., 2013b" in the Reference list.
Line 555: Karanasiou et al., 2014. There is "Karanasiou, 2014" in the Reference list.
The is no reference made within the text to the following references that are in the Reference list:
Amato et al., 2011.
Khalaf et al., 1982.
Zhao et al., 2015.
The references in the Reference list are not always in the appropriate order:
"Carslaw et al., 2006" should come after "Carslaw and Ropkins, 2012".
"Dall'Osto et al., 2016" should come after "Dall'Osto et al., 2013".
"Hueglin et al., 2005" should come after "Huang, W. et al., 2012".
In case "Karanasiou, 2014" is correct, it should come before "Karanasiou et al., 2012".
"Liu, S. et al., 2014" should come before "Liu, Z. et al., 2015".
"Lu et al., 2008" should come after "Lough et al., 2005".
Furthermore:
Line 520: Replace "Suess et al." by "Suess".
Line 791: Replace "R. A., and" by "R. A. and".

Further comments for the Main text:
Line 25: Replace "at Shanghai" by "at the Shanghai".
Line 28: Replace "Elements related" by "Element-related".
Line 30: Replace "atmospheric" by "the atmospheric".
Line 33: Replace "of elements in" by "of the elements in the".
Line 34: Replace "in brackets" by "in parentheses".
Line 35: Replace "melting" by "smelting".
Line 37: Replace "Contributed by exhaust and non-exhaust vehicle emissions," by "The contribution from the exhaust and non-exhaust vehicle emissions, i.e., the".
Line 38: Replace "shows strong" by "shows a strong".
Line 39: Replace "during rush" by "during the rush" and replace "Shipping" by "The shipping".
Line 40: Replace "almost" by "are almost".
Line 41: Replace "transported from East" by "transported from the East" and replace "fallen" by "falls".
Line 42: Replace "V/Ni in" by "V/Ni ratios in".
Line 43: Replace "K were derived" by "the K was derived".
Line 45: Replace "to trace" by "to the trace".
Line 47: Replace "of trace" by "of the trace".
Line 48: Replace "lower" by "lower the concentration of the".
Line 50: Replace "in urban" by "in the urban".
Line 61: Replace "refers" by "referring".
Line 63: Replace "with unique" by "unique".
Line 67: Replace "on aerosol" by "on the aerosol".
Line 69: Replace "elements components" by "elemental components".
Line 70: Replace "exerted a" by "exert a".
Line 77: Replace "elements species" by "elemental species".
Line 87: Replace "of elemental" by "of the elemental".
Line 92: Replace "in ambient" by "in the ambient".
Line 96: Replace "trace elements" by "trace element".
Line 102: Replace "for elements" by "for elemental".
Line 108: Replace "ambient elements" by "ambient elemental".
Line 109: Replace "trace elements" by "trace element".
Line 120: Replace "National" by "the National".
Line 124: Replace "and Xact" by "and the Xact".
Line 126: Replace "ambient elements" by "ambient elemental".
Line 128: Replace "reactive filter tapes" by "a moving filter tape" and replace "by US" by "by the US".
Line 138: Replace "trade, which has" by "trade and has".
Line 141: Replace "trace elements" by "trace element".
Line 147: Replace "elements species" by "elemental species".
Line 159: Replace "of trace elements will be investigated to examine if water spay" by "of the trace elements was investigated to examine if water spray".
Line 160: Replace "trace elements" by "trace element".
Lines 182 and 183: Replace "Pudong" by "the Pudong".
Line 184: Replace "Pudong" by "The Pudong".
Line 185: Replace "For PEMC" by "For the PEMC".
Line 188: Replace "indicted in Fig. 1c, PEMC" by "indicated in Fig. 1c, the PEMC" and replace "emissions sources" by "emission sources".
Line 193: Replace "PEMC" by "the PEMC".
Lines 212-213: Replace "of Xact" by "of the Xact" and replace "on blank Nuclepore" by "on a blank Nuclepore filter".
Line 228: Replace "elemental analysis" by "the elemental analysis".
Line 233: Replace "using" by "using the".
Line 238: Replace "collected by the" by "for the".
Line 242: Replace "by Shanghai" by "by the Shanghai".
Line 243: Replace "PEMC" by "the PEMC".
Line 260: Use superscript for "th" in "kth".
Line 268: Replace "elements in" by "elements in the".
Line 276: Replace "et al. 1998" by "et al., 1998".
Line 284: Replace "with BS" by "with the BS".
Line 293: Replace "with similar" by "with a similar".
Line 312: Replace "has described" by "has been described".
Line 316: Replace "of hourly" by "of the hourly".
Line 317: Replace "at PEMC" by "at the PEMC".
Line 323: Replace "summaries" by "summary".
Line 325: Replace "are also shown" by "are shown".
Line 331: Replace "ambient average mass concentrations of elemental" by "the ambient average mass concentrations of the elemental".
Line 332: Replace "between detection" by "between the detection".
Line 342: Replace "airborne" by "the airborne".
Line 345: Replace "on total" by "for the total".
Line 350: Replace "concentration as" by "concentration was", replace "which accounting" by "accounting", and replace "of total" by "of the total".
Line 363: Replace "although a huge" by "a huge".
Line 365: Replace "were given" by "was given".
Line 372: Replace "trace elements" by "trace element".
Line 374: Replace "an order or two" by "one or two".
Line 375: Replace "ranged in the same level as industrialized city" by "were of the same level as in industrialized cities".
Lines 376 and 377 and within Table 1: Use the same city name, either Gwangju or Kwangju.
Line 377: Replace "that of" by "those at".
Line 381: Replace "trace elements" by "trace element".
Line 382: Replace "elements species" by "elemental species".
Line 384: Replace "trace elements" by "trace element".
Line 390: Replace "of the constant" by "of a constant".
Line 392: Replace "explained by" by "obtained with".
Line 403: Replace "to factor" by "to the factor" and replace "sources to" by "sources to the".
Line 408: Replace "the variation" by "the concentration".
Line 410: Replace "In urban" by "In the urban".
Line 415: Replace "tracers for" by "tracers for a".
Lines 417-418: Replace "origins typically" by "origin is typically".
Line 425: Replace "assigned to" by "assigned to a".
Line 432: Replace "of trace" by "of the trace".
Line 434: Replace "hours are" by "hours that are".
Line 435: Replace "of traffic" by "of the traffic".
Line 438: Replace "comes almost" by "come almost".
Line 443: Replace "from east" by "from the east".
Line 444: Replace "from costal" by "from the coastal".
Line 447: Replace "Recent" by "A recent".
Line 450: Replace "in urban" by "in the urban" and replace "with slightly" by "with slight".
Line 458: Replace "during four" by "during the four".
Line 459: Replace "of trace elements in Shanghai" by "of the trace elements in the Shanghai".
Line 460: Replace "its share" by "their share" and replace "in harbor" by "in the harbor".
Line 461: Replace "Shanghai and its" by "Shanghai and the".
Line 463: Replace "in main engines of ships" by "in the main engines of the ships".
Line 464: Replace "on air" by "on the air".
Line 469: Replace "form of" by "forms of".
Line 471: Replace "during roasting" by "during the roasting".
Line 475: Replace "to total" by "to the total".
Line 483: Replace "shows Au" by "shows that Au".
Line 484: Replace "that different from Ag" by "which is different from that for Ag".
Line 487: Replace "Therefore, element" by "Therefore, the element".
Line 491: Replace "the variation" by "the concentration" and replace "and unexpected" by "and an unexpected".
Line 495: Replace "norther China" by "northern China".
Line 502: Replace "from norther China can transport air" by "from northern China transporting air".
Line 503: Replace "to Shanghai" by "to the Shanghai".
Line 505: Replace "of PM2.5" by "of the PM2.5".
Line 507: Replace "elements concentrations" by "elemental concentrations".
Line 509: Replace "was considered to be originated" by "is considered to originate".
Line 511: Replace "of element K in urban Shanghai were" by "of the element K in urban Shanghai was".
Line 512: Replace "maybe that" by "may be that".
Line 514: Replace "has high" by "has a high".
Line 519: Replace "contained relatively" by "contained a relatively".
Lines 520-521: Replace "in which they detected" by "who observed".
Line 522: Replace "i.e." by "i.e.,".
Line 523: Replace "ATOFMS" by "the ATOFMS".
Line 526: Replace "the explained variation" by "the concentration".
Line 530: Replace "of world" by "of the world".
Line 536: Replace "Since element Cr is reported to be transported over distances by air" by "Since the element Cr is reported to be transported over substantial distances by the air".
Line 540: Replace "of PM2.5" by "of the PM2.5".
Line 550: Replace "particles on the road surface" by "particles".
Line 551: Replace "atop tall" by "atop a tall".
Line 555: Replace "influence PM" by "influence the PM".
Line 556: Replace "of precipitation" by "of the precipitation".
Line 557: Replace "elements concentration" by "the elemental concentrations".
Line 560: Replace "of trace" by "of the trace".
Line 561: Replace "The precipitation" by "A precipitation".
Lines 563 and 564: Replace "should less" by "should be less".
Line 567: Replace "treated as" by "treated as a".
Line 568: Replace "with the duration" by "with a duration".
Line 572: Replace "Fig. S13" by "Fig. S14".
Lines 572-573: Replace "scavenge and remove" by "scavenges and removes".
Line 574: Replace "should lower" by "should be lower".
Line 576: Replace "ambient elements mass" by "the ambient elemental mass".
Line 578: Replace "lasted" by "which lasted".
Line 582: Replace "The variation" by "Variation".
Line 585: Replace "decrement rate of Zn" by "decrease of the Zn".
Line 588: Replace "were aggregated" by "was aggregated" and replace "Before" by "Before the".
Lines 589-590: Replace "than that during" by "than those during the".
Line 591: Replace "reduce PM2.5" by "reduce the PM2.5" and replace "After precipitation" by "After the precipitation".
Line 593: Replace "than that during" by "than during the" and replace "potential" by "a potential".
Line 595: Replace "as the most" by "as a most" and replace "reflect the" by "reflects the".
Line 597: Replace "decrement rate of Zn concentration and" by "decrease of the Zn concentration and the".
Line 599: Replace "lower ambient" by "lower the ambient".
Line 601: Replace "3.3.1" by "3.3.2".
Line 610: Replace "source mainly includes" by "sources mainly include".
Line 611: Replace "road surface" by "road surfaces".
Line 612: Replace "of coal" by "of the coal".
Line 613: Replace "and Hg have" by "and Hg having a".
Line 614: Replace "of coal" by "of the coal".
Line 616: Replace "different from traffic-related source, coal" by "different from the traffic-related source, the coal".
Line 619: Replace "kept quite" by "remained quite".
Line 626: Replace "The variation" by "Variation".
Line 632: Replace "from Eastern" by "from the Eastern".
Line 633: Replace "to urban" by "to the urban".
Line 638: Replace "from Eastern China sea and then accumulated in" by "from the Eastern China sea which then accumulated in the".
Line 641: Replace "China can" by "China which can".
Line 643: Replace "in Shanghai" by "in the Shanghai".
Line 646: Replace "roses plots" by "roses".
Line 648: Replace "bracket" by "parentheses".
Line 652: Replace "multi-metal monitor" by "multi-metals monitor".
Line 661: Replace "of metal related species comprised" by "of the metal related species amounted to".
Line 664: Replace "measurement and" by "and".
Line 667: Replace "melting" by "smelting".
Line 669: Replace "of ambient" by "of the ambient".
Line 672: Replace "in urban" by "in the urban".
Lines 674-675: Replace "sources of emission" by "emission sources".

Comments for the Supplement:
The Supplement would benefit from numbering the pages.
Page 2: The regression data in Table S1 contain too many significant figures. Two significant figures suffice in case the first significant figure is larger or equal than 2, and when the first significant figure equals 1, three significant figures can be used.
Page 3, first line: Replace "Text S2" by "Table S2" and replace "precipitation chosen" by "precipitation events chosen".
Page 4, line 1: Replace "Text 1" by "Text S1".
Page 4, line 13: Replace "Table below" by "Table S3" and replace "95 of BS" by "95 of the BS".
Page 4, line 14: Replace "50 of BS" by "50 of the BS".
Page 4, line 15: Replace "and other" by "and the other" and replace "95 of BS" by "95 of the BS".
Page 4, line 6 from bottom: Replace "perform PMF" by "performs PMF".
Page 4, line 3 from bottom: Replace "Table below" by "Table S4".
Page 5, line 1 below Table S4: Replace "of BS and DISP method" by "of the BS and DISP methods".
Page 5, line 5 below Table S4: Replace "for PMF" by "for the PMF".
Page 5, line 6 below Table S4: Replace "When factor" by "When the factor".
Page 5, line 7 below Table S4: Replace "than from 4- to 5-factor" by "than is the case when going from the 4- to the 5-factor" and replace "However, a" by "The".
Page 5, line 8 below Table S4: Replace "predetermined" by "selected".
Page 6, line 10: Replace "781" by "781-797".
Page 7, line 1 of figure caption: Replace "Figure 2. Seasonal variations" by "Figure S2. Seasonal variation".
Page 9: I do not see any wind direction information in Figure S4. Should ", and wind directions" not be deleted in the figure caption?
Page 15, line 3 of caption of Figure S10: Replace "Below the diagonal of the diagonal" by "Below the diagonal".
Page 18, caption of Figure S13: Replace "The distribution of precipitation" by "Distribution of precipitation events".
Page 19, line 1 of caption of Figure S14: Replace "The variation" by "Variation".

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AR by Yunhua Chang on behalf of the Authors (29 May 2018) Author's response Manuscript

ED: Publish subject to minor revisions (review by editor) (21 Jun 2018) by Willy Maenhaut

The authors could have addressed some of the comments of the two Anonymous Referees and of myself in a better way.
The comments of Anonymous Referee #6 about "Precipitation effect" should be properly taken into consideration, in particular, "how do the authors explain that Au and Cr increase during the rainfall"; consequently, revision is needed within section 3.3.1.
Also my comment about significant figures was definitely not properly addressed.
Furthermore, the authors failed to address several corrections, which I listed in my previous report. They are listed again. Besides, I have a few new corrections, including regarding the wording and grammar in the new sections of text.
Consequently, additional revision is needed before this manuscript can be accepted for publication in ACP.

Main comments for the Main text:
1. Page 13, within Figure 2 (and on various other occasions in the manuscript, e.g., in Table 1, data for this study; in line 339; within Figure 3; in line 409; in line 427): The concentration data contain too many significant figures (digits). Two significant figures suffice in case the first significant figure is larger than (or equal to) 2, and when the first significant figure equals 1, three significant figures can be used. For example, in Table 1 the authors' data should become as follows: Ba 24, Ca 192, Fe 410, K 390, Mn 32, Pb 27, Si 640, Zn 120.
2. There are still problems with the References.
The following references to which is referred within the text are not in the Reference list:
Line 261: Paatero and Tapper, 1994.
Line 281: Polissar et al., 1998.
There is no reference made within the text to the following reference that is in the Reference list:
Pentti and Unto, 1994.
The references in the Reference list are not always in the appropriate order:
"Karanasiou, 2014" should come before "Karanasiou et al., 2011".
"Liu, S. et al., 2014" should come before "Liu, Z. et al., 2015".
Furthermore:
Line 960: Replace "L., and" by "L. and".

Further comments for the Main text:
Line 28: Replace "Elements-related" by "Element-related".
Line 48: Replace "of trace" by "of the trace".
Line 59: Replace "Pope III et al., 2002; Pope III et al., 2009" by "Pope III et al., 2002, 2009".
Line 110: Replace "trace elements" by "trace element".
Line 115: Replace "Visser et al., 2015b; Visser et al., 2015a" by " Visser et al., 2015b, 2015a).
Line 142: Replace "trace elements" by "trace element".
Line 174: Replace "airflow" by "the airflow".
Line 175: Replace "which will" by "and it will".
Line 187: Replace "Pudong New" by "the Pudong New".
Line 237: Replace "using" by "using the".
Line 238: Replace "different methods" by "different measurement methods".
Line 239: Replace "to measure and different filters (glass filter vs. cellulose filter) to collect trace elements" by "and different collection substrates (glass filter vs. cellulose filter)".
Line 240: Replace "were reported in Table S2. In general, elements" by "are reported in Table S1. In general, the data for elements" and replace "Au were" by "Au".
Line 446: Replace "costal port" by "coastal port".
Line 457: Replace "20014" by "2014".
Line 568: Replace "should less" by "should be less".
Line 598: Replace "than that during" by "than during".
Line 603: Replace "and rainfall" by "and the rainfall".
Line 666: Replace "accounted to" by "amounted to".

Comments for the Supplement:
The Supplement would benefit from numbering the pages.
Page 2: The regression data in Table S1 contain too many significant figures (digits). Two significant figures suffice in case the first significant figure is larger than (or equal to) 2, and when the first significant figure equals 1, three significant figures can be used.
Page 5, line 1 below Table S4: Replace "DISP method" by "DISP methods".
Page 5, lines 5-6 below Table S4: Replace "Figure below" by "Figure S1".
Page 5, line 7 below Table S4: Replace "from 4- to 5-factor" by "from the 4- to the 5-factor".
Page 5, line 8 below Table S4: Replace "predetermined" by "selected".
Page 6, line 10: Replace "781-791" by "781-797".
Page 18, caption of Figure S13: Replace "The distribution of precipitation" by "Distribution of precipitation events".
Page 19, line 1 of caption of Figure S14: Replace "Figure 14" by "Figure S14" and replace "The variation" by "Variation".

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AR by Yunhua Chang on behalf of the Authors (14 Jul 2018) Author's response Manuscript

ED: Publish subject to minor revisions (review by editor) (28 Jul 2018) by Willy Maenhaut

AR by Yunhua Chang on behalf of the Authors (29 Jul 2018) Author's response Manuscript

ED: Publish as is (06 Aug 2018) by Willy Maenhaut

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Short summary

We continuously performed a one-year and hourly-resolved measurement of 18 atmospheric elements in PM_2.5 in Shanghai megacity. Here our high time-resolution observations over a long-term period provide baseline data with high detail, which are of great use for examining acute exposure of morbidity and mortality risk in association with PM_2.5 metal species in China's megacities.