Insights into characteristics, sources, and evolution of submicron aerosols during harvest seasons in the Yangtze River delta  region, China

Zhang, Y. J.; Tang, L. L.; Wang, Z.; Yu, H. X.; Sun, Y. L.; Liu, D.; Qin, W.; Canonaco, F.; Prévôt, A. S. H.; Zhang, H. L.; Zhou, H. C.

doi:https://doi.org/10.5194/acp-15-1331-2015

Articles | Volume 15, issue 3

https://doi.org/10.5194/acp-15-1331-2015

© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/acp-15-1331-2015

© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 15, issue 3

Research article

|

06 Feb 2015

Research article |

| 06 Feb 2015

Insights into characteristics, sources, and evolution of submicron aerosols during harvest seasons in the Yangtze River delta region, China

Y. J. Zhang, L. L. Tang, Z. Wang, H. X. Yu, Y. L. Sun, D. Liu, W. Qin, F. Canonaco, A. S. H. Prévôt, H. L. Zhang, and H. C. Zhou

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Final revised paper (published on 06 Feb 2015)
Supplement to the final revised paper
Preprint (discussion started on 04 Apr 2014)
Supplement to the preprint

Interactive discussion

Status: closed

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

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RC C2083: 'Review of “Insights into characteristics, sources and evolution of submicron aerosols during harvest seasons in Yangtze River Delta (YRD) region, China” by Zhang Y.J. et al.', Anonymous Referee #2, 05 May 2014
RC C4922: 'Review for Zhang et al.', Anonymous Referee #3, 15 Jul 2014
AC C6633: 'Response to the two referees’ comments', Lili Tang, 07 Sep 2014

Peer-review completion

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

AR by Lili Tang on behalf of the Authors (07 Sep 2014) Author's response Manuscript

ED: Reconsider after major revisions (27 Sep 2014) by Willy Maenhaut

The language and grammar of the authors’ replies to the referee comments are rather weak. Therefore, the replies are somewhat difficult to follow. Anyway, referee #3 had very major comments for the ACPD version and I feel that he should be invited to have a look at the authors’ replies and at the revised version to decide whether his comments were properly addressed and to assess to which extent the revised manuscript needs further revision. Also referee #2 of the ACPD version and new referees are invited to review the revised version.

Furthermore, I have several comments and technical corrections myself, so that further revision is definitely needed.

Main text:
The language and grammar should certainly be improved.
Lines 38-39: It is not clear what BBOA represents here. Is it only “fresh biomass burning OA” or the sum of “fresh biomass burning OA” and “biomass burning-influenced OA”?
Line 49: “Ge et al., 2011” is not in the reference list.
Line 54: “Bougiatioti et al., 2013” is not in the reference list.
Line 66: Replace “identify the sources apportionment” by “identify and apportion the sources”.
Line 75: Replace “were developed” by “was developed”.
Line 95: Replace “is resolved” by “are analyzed”.
Line 103: Replace “of about” by “of”.
Line 110: Replace “In this study, the” by “The”.
Line 116: Replace “negligible” by “ negligibly”.
Line 123: Acronyms and abbreviations (here “NR”) should be defined (written full-out) when first used.
Line 135: Replace “detection limits” by “detection limit”.
Line 157: Replace “And the pure” by “Pure”.
Line 162: Replace “a RIE” by “the RIE”.
Line 175: Replace “was also applied” by “was applied”.
Line 178: Replace “combing” by “combining”.
Line 199: “Young et al., 2014” is not in the reference list.
Line 263: Replace “shown in” by “seen in”.
Line 263: Replace “presents the” by “presents”.
Lines 280-281: “This means the non-volatile and character” should be rephrased.
Line 376: Replace “were characterized” by “ was characterized”.
Line 379: Replace “mass spectrums” by “mass spectra”.
Line 388: “Zhang et al., 2005c” is not in the reference list.
Line 393: Replace “thorough the” by “through the”.
Line 393: Replace “slightly increase” by “slight increase”.
Line 404: Replace “mass spectrums” by “mass spectra”.
Line 431: It is unclear what is meant by “the increase of temperature condition”.
Line 440: Replace “show a similar trend with” by “shows a similar trend as”.
Line 442: Replace “recent filed” by “recent field”.
Line 444: “Robinson et al., 2007” is not in the reference list.
Line 457: Replace “Pear River Delata” by “Pearl River Delta”.
Line 475: “to some discusses in” should be reworded.
Line 476: Replace “than that in” by “than in”.
Line 480: “Lathem et al., 2013” is not in the reference list.
Line 485: Replace “than that in” by “than in”.
Line 492: Replace “are much” by “is a much”.
Line 493: Replace “have also been” by “have been”.
Line 499: Replace “maintained at a” by “remained at a”.
Line 530: “for explaining the OOA-BB loadings depended on” should be rephrased.
Line 540: Replace “equations of” by “equation of”.
Line 557: Replace “have also been” by “have been”.
Line 594: Acronyms and abbreviations (here “BTs”) should be defined (written full-out) when first used.
Line 611: Replace “associated” by “is associated”.
Line 618: Replace “that a” by “a”.
Line 621: Replace “sources emission play” by “sources play”.
Line 651: Replace “than that” by “than”.
Line 662: Replace “to the sulfate” by “to that of sulfate”.
Line 667: Replace “equations of” by “equation of”.
Line 676: Replace “are mainly” by “is mainly”.
Lines 691-692: “Andreae and Merlet, 2001” should come after “Allan et al., 2010”.
Lines 693-695: “Alfarra et al., 2007” should come after “Aiken et al., 2010”.
Lines 875-877, lines 881-882, lines 897-899, lines 918-920, lines 926-927, lines 969-971, and lines 993-994: The title of journal articles should be in lower case instead of in title case.
Lines 878-880: “Lipsky et al., 2007” should come after “Li et al., 2017”.
Line 1048: Replace “Averagely relative” by “ Average relative”.
Line 1050: Replace “Pear River” by “Pearl River”.
Line 1060: Replace “(orange) harvests” by “harvest (orange)”.
Line 1076: Replace “are represented for” by “indicate”.

Supplementary Information:
Table S4, second line of heading: Replace “showed in” by “showed” and replace “will be” by “are”.
Table S5, second line of heading: Replace “showed in” by “showed” and replace “will be” by “are”.
Figure S1, third line of caption: Replace “1km” by “1 km”.
Figure S4, first line of caption: Replace “plots show the” by “plots of the”.

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AR by Lili Tang on behalf of the Authors (16 Oct 2014) Author's response Manuscript

ED: Referee Nomination & Report Request started (16 Oct 2014) by Willy Maenhaut

RR by Anonymous Referee #2 (24 Oct 2014)

RR by Anonymous Referee #4 (27 Oct 2014)

Suggestions for revision or reasons for rejection

General Comments

1. Overall, the language and grammar could be improved, as I found a number of instances were I could not quite understand the sentence. I have highlighted a number of these below however the authors are advised to thoroughly check the whole manuscript.

2. My main comment is regarding the manuscript is that the authors appear to not consider local or other sources of biomass burning apart from agricultural residue burning. While the authors state that there is negligible local biomass burning, based on their findings I am not sure that the authors can discount local source influences. I realize that the measurements were taken during summer and autumn and so the contribution from domestic heating would be minimal, however this does not exclude local emissions.
The authors identify with PMF a fresh and an oxidized BBOA source factor, and while I am convinced that are two distinct BBOA sources, I am not sure about attributing the source of both of these factors to the agricultural residue fires.
How far away are the harvest fires from the sampling site, as they appear to be a considerable distance from Nanjing in Figure S1?
As the authors mention in the manuscript, primary BBOA emissions will rapidly oxidize in the atmosphere and if the fires are a fair distance, would not the BBOA have been mostly oxidized by the time they reach the receptor site? Or to put it another way, how can you ‘see’ fresh biomass burning aerosols from these agricultural residue fires?
Furthermore, as mentioned by the authors in the manuscript, differing fuel, burn conditions and efficiency will affect the chemical composition of primary BBOA. In previous work with aerosol mass spectrometry, the differing fuels and burning conditions was put forward as the reason for finding two biomass burning source factors (e.g. Young et al. 2014). Therefore rather than fresh and aged BBOA from the same source (agricultural fires), could not the BBOA factor be more from local emissions of a different source (with differing fuel, etc.) and the OOA-BB more related to the agricultural fires?

3. I think that the title should be changed slightly to reflect that the focus of the work is on biomass burning emissions of agricultural waste during the harvest season.

Specific comments
1. Page 3, line 61. The authors state that farmers burning agricultural residues may result in BB emissions, surely this WILL result in biomass burning emissions?

2. Page 4, line 82-83. Suggest rewording this sentence as it is difficult to follow.

3. Page 9, line 218-220. Perhaps the meteorological values (e.g. WS, WD, etc) could go in Table 1, for clarity.

4. Page 10 line 230. “An over estimation was previously suggested by Huang et al. (2011)”.
What was the extent of this over estimation found by Huang et al.? The authors may wish to comment on how much this could have affected the observed correlation between measured and reconstructed PM1 based on Huang et al. findings.

5. Page 10, line 242. “Overall, those species also show a similar contribution between summer and autumn harvest”. To which species are you referring to here? It is not clear in the text, please clarify.

6. Page 11, line 260-1. “This speculation is consistent with the highest loadings of K+, BBOA, OOA-BB, chloride and BC during the summer harvest”.
When were these highest loadings observed? During case 1? Please clarify.

7. Page 11, line 263. From figure 1, case 2 and 3 appear to be at times when the wind came from different directions, from the NW and E, respectively. Earlier in the paragraph it is stated that the agricultural fires are located to the NW of Nanjing, so case 3 also in the direction of agricultural fires? The authors should perhaps clarify this in the text,

8. Page 12, line 280. “This means the non-volatile character of sulfate and its more regional pollution in the YRD region during the summer and autumn harvest.” Please re-word.

9. Page 15, line 366. The peak of the diurnal profile for BBOA is around 8pm, which is usually characteristic of domestic burning, so as mentioned in an earlier comment could this not indicate local emissions?

10. Page 19, line 447-451. “As shown in Figure S4, for the BB-emissions related OA (including BBOA and OOA-BB), they show a very similar wind rose pattern with high concentration from southeasterly wind during the summer harvest, and from northerly wind during the autumn harvest. This further supports that the production of OOA-BB is related to the BB plumes.”
From Figure S1, the main concentration of agricultural fires appear to be to the NW of Nanjing during the summer, how does corroborate with highest concentrations coming from the SE, particularly for BBOA? A similar trend is also observed in the autumn, with the highest BBOA and OOA-BB concentrations coming from SE whereas the fires mainly appear to be concentrated in the west (Fig S1). How
A more useful analysis may be to also include wind speed, such as a polar plot (where concentrations are plotted as a function of both wind direction and speed), which could indicate the whether local or regional emissions were contributing and their direction.

11. Page 20, line 475. “This is also corresponding to some contention discussed in section3.2.3.” Please re-word, to what contention are you referring?

12. Page 20, line 489. “. Therefore, these findings indicate that BB contributes more fractions on organics than that on the secondary inorganic aerosols in the transported pollution air masses.” Please re-word, not quite sure what you are trying to say.

13. Page 21, line 496. I am not sure what Fig 8 adds to the analysis based on the discussion that it not already shown in Fig 7 and so Fig 8 could perhaps be removed but will leave that for the authors to decide.

14. Page 23, line 5559-562. How is a higher f44 a factor for the observed higher oxidation levels during summer? Is not the f44 a measure of OA oxidation and so how can the f44 be a factor for the observed higher oxidation levels during summer?

15. Page 25, line 616, “The contributions of BC, HOA + COA, and BB related OA (BBOA and OOA-BB) to PM1 are rather high in the WC BTs”. However, my understanding of Fig 13 is that the % contributions for these species did not change that much during the summer harvest and perhaps the authors may wish to clarify this statement.
Overall, I found the discussion in Section 3.6 a little hard to follow and would recommend that the authors review this section.

16. Page 27, line 659-661. “This suggests that OOA-BB may be quickly oxidized a bit and condensed on the particle phase during the nighttime with the high RH and low T conditions.” Please re-word.

17. Figure 3. Why have you used results by Crippa at al. (2013) from Paris as reference mass spectra and not those obtained locally such as He et al. (2010) or Huang et al. (2013)?

18. Included in Fig 9 are measurements taken during July 2013, as they are considered to have no biomass burning influence. However, I found no mention of these measurements in the Methods. Were these taken at the same location and with the same instrument? Please include a brief description in the methods. Furthermore, to give some context to the measured PM masses during the harvest season in Nanjing, it may be worth including a comparison of the measured PM1 masses during the July measurements.

References
Crippa,M., DeCarlo,P.F., Slowik,J.G., Mohr,C., Heringa,M.F., Chirico,R., Poulain,L., Freutel,F., Sciare,J., Cozic,J., DiMarco,C.F., Elsasser,M., Nicolas,J.B., Marchand,N., Abidi,E., Wiedensohler,A., Drewnick,F., Schneider,J., Borrmann,S., Nemitz,E., Zimmermann,R., Jaffrezo,J.-L., Prévôt,A.S.H., and Baltensperger,U.: Wintertime aerosol chemical composition and source apportionment of the organic fraction in the metropolitan area of Paris, Atmos. Chem. Phys., 13, 961-981, doi:10.5194/acp-13-961-2013, 2013.
He,L.-Y., Lin,Y., Huang,X.-F., Guo,S., Xue,L., Su,Q., Hu,M., Luan,S.-J., and Zhang,Y.-H.: Characterization of high-resolution aerosol mass spectra of primary organic aerosol emissions from Chinese cooking and biomass burning, Atmos. Chem. Phys., 10, 11535-11543, doi:10.5194/acp-10-11535-2010, 2010.
Huang,X.-F., Xue,L., Tian, D.-X., Shao, W.-W.,Sun,T.-L., Gong, Z.-H., Ju, W.-W., Jiang, B., Hu, M., and He,L.-Y.: Highly time-resolved carbonaceous aerosol characterization in Yangtze River Delta of China: Composition, mixing state and secondary formation, Atmos. Environ., 64, 200-207, 2013.
Young, D. E., Allan, J. D., Williams, P. I., Green, D. C., Harrison, R. M., Yin, J., Flynn, M. J., Gallagher, M. W., and Coe, H.: Investigating the two-component model of solid fuel organic aerosol in London: processes, PM1contributions, and seasonality, Atmos. Chem. Phys. Discuss., 14, 20845-20882, doi:10.5194/acpd-14-20845-2014, 2014.

Referee Report: PDF

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RR by Anonymous Referee #3 (04 Nov 2014)

Suggestions for revision or reasons for rejection

In their manuscript “Insights into characteristics, sources and evolution of submicron aerosols during harvest seasons in Yangtze River Delta (YRD) region, China” Zhang and coworkers present results from two two-week measurement periods in summer and autumn 2013 using an Aerodyne ACSM for non-refractory sub-micrometer aerosol components together with a MARGA to measure potassium ions in the aerosol and additional instruments to measure PM1 and black carbon in PM2.5.
The authors discuss characteristics of the ambient aerosol measured during the two periods with a focus on the biomass burning contribution to ambient PM pollution. Diurnal patterns, individual pollution events and contributions from different source regions are discussed. PMF is used to separate four different types of organic aerosol: oxygenated organic aerosol (aged secondary organic aerosol), biomass-burning oxygenated organic aerosol (likely secondary organic aerosol from biomass burning-related precursors), biomass burning organic aerosol (primary organic aerosol from biomass burning), and hydrocarbon-like organic aerosol from traffic and cooking activities. Also for these organic aerosol types diurnal patterns and source regions are discussed to obtain a more complete picture of the harvest-related biomass burning contribution to ambient PM pollution during the harvest times.
This is the second version of the manuscript that was submitted to ACPD which includes major changes compared to the first version. The authors improved the manuscript significantly regarding the two major points in my review for the first version: The current version of the manuscript is much more focused compared to the first version and many conclusions that were not based on the presented data have been changed or removed. Even though the authors focused their work much more than in the previous version, this manuscript is still quite long, especially with a very large number of figures. In my first review I wrote that the manuscript has 13 Figures with additional 5 Figures in the supplementary information which were also referenced in the text. Now the manuscript has 13 Figures with 15 (!) additional Figures in the supplement.
Most of the comments in the first review have been answered and treaded satisfactorily. Nevertheless, there are still many shortcomings of the manuscript in many locations of the text. However, these issues are much less serious compared to the previous version of the manuscript. Since the manuscript is now much better focused and since generally the data are well analyzed and the results are well founded on the data, I think that it can be published in ACP with only minor (although not really few) revisions after the detailed comments below are taken into account. Generally, I suggest that the authors ask a native English speaker to proofread the text. There are still many sections in the text that are confusing.

Detailed comments:
P1L4-5: While the content of the manuscript did not change a lot and mainly PMF has been re-done, ending up with a different selection of factors, the authors list grew by two persons from PSI, Switzerland. Such a contribution to one detail of the content of a manuscript could also be honored in the acknowledgements.

P2L29: According to the authors Nanjing has 8 million inhabitants. This is below the threshold of 10 million above which a city is called “megacity”. (also: P5L103)

P2L35: OOA-BB does not dominate 80% of total BBOA but contributes 80% to total BBOA.

P2L37-38: High RH and low T do not facilitate the formation of semi-volatile species (this is a chemical process) but supports the partitioning of such species into the particle phase.

P2L40-41: “The OA mass decreases with the aging of BB plumes, indicating that the fresh BB plumes contribute to the OA burden significantly.” How is this conclusion an inevitable result of these findings?

P2L43: Change “… high BB pollutants are linked …” into: “… high BB pollutant concentrations are linked …”. Not only BB pollutants are linked to these source areas, also other pollutant concentrations are increased for air masses from these continental source areas (as expected) compared to marine source areas. This is not necessarily a result of biomass burning.

P3L58: Change “… a large number of agricultural crop residue …” into “… a large amount of agricultural crop residue …”

P3L61: Change “… which may result in BB emission.” into “… which results in BB emissions.”

P3L61-63: “The understanding of the compositions, sources and processes of atmospheric aerosol particles during harvest seasons is urgently needed to design measures to improve the quality of air in China.” It probably would be much more efficient to simply reduce biomass burning by the farmers on the fields in order to improve air quality.

P4L80-81: “However, limited information is available for estimating the source apportionment of BBOA.” What is the information of this sentence?

P5L98-99: “source” and “origin” is twice almost the same.

P5L112ff: These sentences need some major rewording. In addition: There are no agricultural fields in the urban Nanjing area. This means that all BB emissions are transported “dozens to hundreds of kilometers” before reaching the measurement site. With the average wind speed of 2.5 m/s this means that the transport time is in the order of 11 hours (for one hundred km). So a significant delay in the maxima of pollutants from BB burning would be expected compared to the times when the fires are burning (during night). This is not observed in the diurnal patterns.

P6L127: Use “l min-1” instead of “L min-1” (also line 135) and use “cm3” instead of “cc”.

P6L129: Is the mass spectrometer really scanned with a rate of 500 ms amu-1 ? This means that a single scan takes 70 seconds.

P6L135-138: Be consistent in how to name instruments. In line 135 you write “The MET ONE BAM-1020” while in line 138 you write “… a gas analyzer (Thermo Scientific, Model 48i).”

P6L140: What is a ground meteorology station?

P7L157-158: I assume NH4NO3 particles are not used for “quantitative measurements” but for the calibration of the instrument.

P7L162: Explain what “response factor” is.

P8L177-178: What do you mean with the sentence “Furthermore, the OA …”?

P8L180: PMF was not restricted to m/z 120 but “up to m/z 120” or “to m/z 10 – 120”.

P8L182-183: Fpeaks were not varied in steps of 0.1 during the summer and autumn harvest but fpeaks were varied in steps of 0.1 for the data of the summer and autumn harvest.

P9L197: How can the 4-factor solution be “valid”? PMF cannot separate different types of organic aerosol that in reality exist. PMF can only be used to describe the organic aerosol using different factors, i.e. types of organic aerosols. These factors are never “valid”, they can just describe the total aerosol better or worse. Therefore the PMF solution of the previous version of the manuscript was not “wrong” or “invalid” and this solution is now not “valid”, but this solution describes the total OA better than the previous one and provides more information.

P9L208: Why were back trajectories calculated for 500 m arrival height while the measurements were performed at 18 m above ground level? Are there significant differences in back trajectories calculated for ground level and for 500 m?

P10L227-230: Why may PM1 be overestimated due to the uncertainties in the conversion of the measured signals into mass concentrations? It also could be underestimated.

P10L233-236 and L238-240: The first of these two sections is in contradiction to the second one. According to the second of these sections OA is similar during both harvest seasons while for the other species except nitrate during summer the fractions are smaller. According to the first of these sections all species are similar for both harvest seasons with the exception of BC, for which during autumn harvest a larger fraction was found.

P10L240f: What is consistent with the findings in these other papers? The dominance of OA in ambient PM1 is consistent all over the world (e.g. Jimenez et al., Science, 2009).

P11L246ff: Wind direction is also an important meteorological factor affecting PM. This should be named not only in line 246 but also in line 249 as an important factor that can cause dramatic changes in PM load. What is “dilution of the atmosphere” (line 249)?

P11L256-262: The explanation provided for case 1 provides little evidence for such a sharp, short and intense peak as observed in the data.

P11L262-265: Again this explanation fails in explaining what causes these sharp and intense peaks.

P11L265-267: How is this a conclusion from the previous sentences? There is no reasonable explanation for the sharp and intense peaks. There is also no reasonable explanation what biomass burning has to do with these peaks.

P12L275: Check the times of the peaks in the diurnal patterns (also P13L299-300). How can the OA peak around 19:00-22:00 be “in agreement with the emission behaviors of pollution sources, i.e. (…) BB emissions”? BB emissions are during the night. Transport times for the average wind speed and the typical distance of the sources is in the order of 10 hours or more. So they should arrive not before the early morning.

P12L279 and L282: Sulfate does not show any significant diurnal trend and not a “weaker diurnal variation” (L279). Therefore a “similar diurnal trend” (L282) does not make sense.

P12L282-285: The lower nitrate concentrations during the day and higher values during the night is not necessarily a harvest-related feature. This is probably due to the partitioning of nitrate between gas- and particle phase and is related to RH and T.

P13L298-306: For the identification of the BB contribution to the ambient PM burden and to separate it from the contribution from other sources it would be very helpful to have diurnal patterns for the non-harvest times between the two harvest seasons. As it is right now the discussion on the BB contribution is to a large degree speculation – especially if one takes into account the large travel times (and related unknown delays in arrival time) BB emissions need to reach the sampling site.

P14L335-339: This is a strange result. Does this mean that the location of the main traffic and cooking sources changed from summer until autumn?

P14L343: How do you know that m/z 60 is almost all C2H4O2+ without any high resolution mass spectra?

P15L345-356: Check the language of this paragraph.

P15L359: Change “… this factor might be fresh/primary BBOA …” into “… this factor might be associated with fresh/primary BBOA …”. You cannot identify a PMF factor with a certain type of organic aerosol, it can only be a reasonable representation of OA.

P15L364: Do you have an explanation why the correlation between BBOA and K+ is so different during the two harvest seasons?

P15L365: Add “(Fig. 3)” between “… at nighttime” and “which is …”.

P16L372: “means” seems too strong. I suggest replacing with “suggests”.

P16L376: Replace “Fig. 3d” with “Fig. 3c and d”

P16L379: The statement on m44 is a repetition of a similar statement two lines above.

P16L384: Replace “As shown in Figure 4d …” with “In Figure 4d …”

P16L386: Do you think that R2 of 0.46 describes still a “good correlation”?

P16L390&393: What is a “stable variation”?

P17L395: OOA is not formed by photochemical processing during the daytime only during the harvest seasons but also during other seasons.

P17L404: Add “and identified” between “… has been resolved” and “as oxidized …”

P17L405: What are “oxidized signals”?

P17L406-407: Replace “… which correlates well with BB-emission …” with “… which correlate well with those of BB-emission …”. Otherwise you state that the m60 correlates with OOA2-BBOA.

P17L417: Replace “burn phase” with “burning conditions”

P18L419-P19L451: This paragraph is not really well structured and leaves the reader with quite a bit of confusion. Here comparisons of the OOA-BB factor mass spectrum with several other mass spectra from the literature are presented. After reading this text the reader is likely confused about the actual meaning of the OOA-BB factor: It could be BBOA mixed with OOA, it could be aged BBOA, it could be secondary OA from gaseous biomass burning-related precursors, it could be BBOA from smoldering. Either this paragraph is better structured to extract solid information on the (likely) nature of OOA-BB or it is clearly stated that the nature of OOA-BB is unknown.
In addition, there are again several statements within this paragraph which are not well based on the data and are more or less speculation or assumptions. This should be marked clearly. If ozonolysis and NO3 reactions are assumed to be the processes that generate OOA-BB from precursors it would be helpful if O3 and NO3 concentrations or relationships between their concentrations and OOA-BB formation would be presented.

P18L432: The OOA-BB time series strongly correlates with “the time series of“ K+ and Delta m/z 60 … (insert “the time series”). Please provide R2 for these correlations to support the “strong”.

P19L449-450: Change “… high concentration from southeasterly wind … and from northerly wind …” into “… high concentration during times with southeasterly wind … and with northerly wind …” or something like this.

P19L459-460: What were the criteria for the separation? What do the percentages mean?

P20L490-493: I suggest changing “contribution” to “fraction”.

P21L499: I do not agree with this statement. According to Figure 8 the total OA fraction does NOT remain at a stable level: It increases from about 15% to 40% and from 30% to 45% during summer and autumn, respectively.

P21L500ff: How many percent is the “significant” increase of OOA-BB and BBOA? Here the impression is given that only an increase of the fraction of a certain particle component with increasing total PM concentration shows a contribution to increased PM. Also components that have constant fractions for all total PM levels contribute to the increase of total PM.

P21L515: “The BBOA mass loadings during the harvest season were estimated using a simple method.” I suggest inserting “a posteriori” between “estimated” and “using” to make clear that this was a calculation that was done after the data analysis was finished. However, it would be more honest not to write that BBOA mass loadings were “estimated”, but to write that Delta m/z60 concentrations correlate with PMF BBOA. Here this correlation is shown once again, BBOA is not estimated.

P22L519: Change “background level” into “background fraction” (also L521 and L523: “value”). What is “little/negligible” BB-influence – how is it defined?

P22L531: What is “mathematically mixing”? The whole sentence is hard to understand.

P22L535-539: If Delta m/z60 correlates with BBOA (as was shown in the text above) it is not surprising that Delta m/z60 multiplied by the ratio of BBOA/Delta m/z60 agrees well with BBOA. This is a trivial result and no Figure is needed to present this. Therefore I suggest removing Figure 10.

P23L545: Explain what Delta CO is and how it was calculated.

P23L549f: This ratio can only remove the effect of dilution of the plume in regional air if there is no other CO source and the dilution air is CO-free. Is this the case?

P23L560: Explain what Delta f44 is.

P23L559-562: Here in two consecutive sentences the same information is given twice. The second sentence is not a consequence of the first one it just repeats the information.

P23L543-562: It is not really clear to me what the reader learns from Figure 11.

P23L566: What is the “result observed by Crippa et al. (2013)” ?

P23L567: HOW does this “further demonstrate(s) that BBOA represents mainly the primary BBOA”? How is this conclusion based on the previous text?

P24L571-576: Where is the evidence in the data that BBOA wanders up the triangle when aging?

P24L578-580 and P24L587: While in the first of the two locations in the text it is clearly stated (and I agree with this) that in Figure 12b no evidence for a dominance of either aging or dilution is presented, in the second location (line 587) only “aging” is named as the underlying process. This is not what the data show!

P23L543-P24L591: All the results presented here show no clear evidence for aging processes of the BB plume! All the effects observed here can also be explained by dilution of the plume only. This should clearly be stated.

P25L594-595: Not back trajectories for every 2 hours are presented in Figure 13 as stated here, but only the cluster back trajectories.

P25L606: Are “the total PM1 loadings” the average PM1 concentrations for the whole cluster-related time intervals?

P25L611: Which “continental-related cluster”? State clearly.

P25L606-613: This finding is similar to what is found almost everywhere on the world. Ambient measurements are typically impacted by the source region of the air that is measured. How are the large concentrations measured for some of the trajectory clusters related to the fire locations?

P25L616-617: I do not completely agree with this statement: According to Figure 13 BC fractions are not larger in WC compared to the other clusters, OOA-BB and HOA/COA are similar in WC and SEM, HOA/COA is less in WC than in EM.

P26L621f: The statement “local sources play an important role in the relatively low PM pollution” sounds quite strange.

P26L624-627: I do not understand what is meant here in this paragraph. In addition: did you confuse “chloride” with “nitrate” in the list of aerosol components in parenthesis?

P26L630-631: I do not understand this sentence.

P26L631-636: The result that marine air masses (EM, NEM) have higher PM concentrations than continental air masses (NC) during autumn is surprising and different to the summer result. This should be discussed.

P27L647-649: The similar diurnal patterns of the secondary species during summer and autumn are probably due to similar chemical processing as stated, but also due to physical processes like gas-particle partitioning which is similar independent of season. I do not think that source emission patterns need to be similar since for this type of aerosol the sources are largely de-coupled from the aerosol measured days later.

P27L659-661: I cannot follow the argument here completely. Do you suggest that OOA-BB is oxidized precursor material that is condensed onto primary BB particles? This is quite unclear here. It could also be oxidized primary particles.

P27L662: Change “reflecting their regional pollution” into “reflecting their regional origin”

P28L667-668: This simple estimate of BBOA using m/z60 was already presented several times. It would be interesting how well this method used here would work in other environments.

P28L671-674: Low pollution levels were associated with marine air masses only during the summer harvest.

Table 1: In this table not the mass concentration of PM1 is shown but the concentrations of the species and OA types within PM1.

Figure 1: The letters (“a)”, “b)”, ..) are missing in the Figure. I have the impression the unit for precipitation is not correct. Is it really “mm”, not “mm/h”?

Figure 3: How well do the mass spectra correlate? R2-values would be interesting. Are the reference spectra from ACSM or from AMS? Do you have an explanation why the spectra from this work show so much more m44 and m28 compared to the reference spectra? Especially for the spectra in b) the reference spectrum is systematically lower than the measured spectra. How can this be if both spectra are normalized to total signal?

Figure 7: All the information on composition in other cities is not discussed in the text. Either discuss this information or remove it from the graph.

Figure 11: While the fits are probably the best approximations of the data points using this fit function, they do not represent the data and the behavior of the data at all.

Figure 12: The yellow scale in panel b) is not very useful since almost all data points have the same color.

Figure 13: The Figure only shows the average (is this correct?) cluster back trajectory. There is no information on the individual trajectories that contribute to the averages. How well do the averages represent all these trajectories within the clusters? Is it possible to visualize this somehow? E.g. instead of showing a single trajectory showing the range of trajectories that is spanned by the individual trajectories within a cluster?

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ED: Reconsider after minor revisions (Editor review) (10 Nov 2014) by Willy Maenhaut

The comments of the three referees should be taken into consideration for preparing a revised version. Besides, I have a number of comments and corrections myself, which have to be addressed.

Main text:
Line 41: Replace “masses back-trajectory” by “mass back-trajectories”.
Line 47: “Ramanathan et al., 2001” is not in the Reference list.
Lines 89-91: This sentence is unclear; it needs to be rephrased.
Lines 113-114: There is something wrong with this sentence; it needs to be rephrased.
Line 189: Replace “is difficult to distinguish the” by “has difficulties distinguishing the”.
Line 198: Replace “found the highly” by “ found highly”.
Line 222: Replace “were shown” by “are shown”.
Line 300: Replace “As previous studies” by “As in previous studies”.
Line 311: Replace “were presented” by “are presented”.
Line 318: Replace “from mass spectrum were characterized as the components” by “ from the mass spectrum were characterized as components”.
Line 368: POA has not been defined; acronyms and abbreviations should be defined (written full-out) when first used.
Line 384: Replace “As shown in Figure 4d, the” by “In Figure 4d the”.
Line 428: Replace “as it will be” by “as they will be”.
Line 430: Replace “shows the relatively” by “ shows relatively”.
Line 442: Replace “filed” by “field”.
Line 444: “Lipsky et al., 2006” is not in the Reference list; there is “Lipsky and Robinson, 2006” in that list, to which no reference is made within the text.
Line 456: Replace “Shanghai), suburban/remote” by “Shanghai) and suburban/remote”.
Lines 506-509: This sentence is unclear; it needs to be rephrased.
Line 623: Replace “account the” by “provide”.
Line 629: It is unclear what “the others” denote.
Line 671: Replace “Air masses” by “Air mass”.
Line 793: Titles of journal articles should be in lower case and not in title case.
Lines 955-959: There is not referred to this reference within the text.

Supplementary Information:
Figure S6a: Replace in the abscissa “Number of factor” by “Number of factors”.
Figure S11a: Replace in the abscissa “Number of factor” by “Number of factors”.
Figure S11, second line of caption: Replace “summer harvest” by “autumn harvest”.

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AR by Lili Tang on behalf of the Authors (20 Nov 2014) Author's response Manuscript

ED: Reconsider after minor revisions (Editor review) (13 Dec 2014) by Willy Maenhaut

AR by Lili Tang on behalf of the Authors (13 Dec 2014) Author's response Manuscript

ED: Publish as is (17 Dec 2014) by Willy Maenhaut

AR by Lili Tang on behalf of the Authors (18 Dec 2014) Manuscript

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Short summary

The chemical composition, sources, and evolution processes of PM1 were investigated with an Aerodyne ACSM during harvest seasons in the Yangtze River delta, China. Two biomass burning organic aerosol (BBOA) factors derived from PMF model were assessed. The oxidized BBOA contributes ~80% of the total BBOA loadings in the BB plumes. Evidence that BBOA may be oxidized to more aged and less volatile organics during the aging process was suggested.