Chemical characterization of submicron aerosol and particle growth events at a national background site (3295 m a.s.l.) on the Tibetan Plateau

Du, W.; Sun, Y. L.; Xu, Y. S.; Jiang, Q.; Wang, Q. Q.; Yang, W.; Wang, F.; Bai, Z. P.; Zhao, X. D.; Yang, Y. C.

doi:https://doi.org/10.5194/acp-15-10811-2015

Articles | Volume 15, issue 18

https://doi.org/10.5194/acp-15-10811-2015

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

Special issue:

Study of ozone, aerosols and radiation over the Tibetan Plateau...

https://doi.org/10.5194/acp-15-10811-2015

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

Articles | Volume 15, issue 18

Research article

|

29 Sep 2015

Research article |

| 29 Sep 2015

Chemical characterization of submicron aerosol and particle growth events at a national background site (3295 m a.s.l.) on the Tibetan Plateau

W. Du, Y. L. Sun, Y. S. Xu, Q. Jiang, Q. Q. Wang, W. Yang, F. Wang, Z. P. Bai, X. D. Zhao, and Y. C. Yang

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Final revised paper (published on 29 Sep 2015)
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Preprint (discussion started on 11 May 2015)
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Interactive discussion

Status: closed

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

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RC C3265: 'Reviewer 1', Anonymous Referee #2, 05 Jun 2015
RC C3385: 'Interactive Comment on “Chemical characterization of submicron aerosol and particle growth events at a National Background Site (3295 m a. s. l.) in the Tibetan Plateau” by W. Du et al.', Anonymous Referee #1, 09 Jun 2015
AC C5995: 'Reply to the two reviewers' comments', Yele Sun, 18 Aug 2015

Peer-review completion

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

AR by Yele Sun on behalf of the Authors (18 Aug 2015) Author's response Manuscript

ED: Referee Nomination & Report Request started (18 Aug 2015) by Xiaobin Xu

RR by Anonymous Referee #2 (25 Aug 2015)

RR by Anonymous Referee #1 (09 Sep 2015)

Suggestions for revision or reasons for rejection

The manuscript entitled, “Chemical characterization of submicron aerosol and particle growth events at a National Background Site (3295 m a. s. l.) on the Tibetan Plateau” by W. Du et al., presents non-refractory plus black carbon (BC) aerosol chemical composition and particle size distribution data from a remote location on the northeastern region of the Tibetan Plateau. This paper is of interest to many readers of Atmospheric Chemistry and Physics and it is important that it is published there.

The authors put much effort and care into responding to the first round of reviewers' comments. The manuscript has improved with this revision. Thank you for making many changes and thank you to the other reviewer for focusing on details that I did not address.

It is apparent that my suggestion to provide an analysis of air mass histories at the site is beyond the scope of this manuscript. The assertion that the air was regionally-transported to the site was not backed by more information on how air was actually getting there on average. Hopefully, data from this paper will be analyzed further by someone who can study the large scale modeling and meteorology. Overall, the manuscript is pretty close to being ready to publish in ACP.

To help put these results in a broader context and make it easier for the global atmospheric community to use, I strongly recommend some simple changes be incorporated into the present manuscript.

1) In lieu of an analysis of air mass histories in the present paper, it would be extremely helpful if there is a paper discussing the meteorology at the site that could be referenced in section 2.1 or perhaps references to other measurements that have been taken at the site in the past, if available.
2) The maps in Figs. 1 and S3 do not show scales - for example, how many km are represented in each of them? Please add that information.
3) For Figure 1, please add to the caption text that the pie charts show data from AMS (non-refractory composition only) plus black carbon. Also, please add to the caption an explanation for the dotted blue lines. Along the same lines, please indicate in the caption for table S1 that all the measurements were using an AMS and in some cases with black carbon.
4) Please put the two altitude profiles of the back trajectories back into the SI, along with an indication of where Xining is on the “Clean 1” trajectory of altitude as function of time back. Please add a note in the caption that the black line is ground level, if that is what it means.
5) The diurnal plots of the meteorological data in the SI are very important, especially when combined with the aerosol and gas phase measurements. The winds appear to be changing from the west to from the south, just at the time that the new particles are detected. If possible, it would be worthwhile to classify these air mass histories. This could be important in further interpreting the new particle formation events.
6) The building was at a higher temperature than ambient and the air sampled by the instrument was in the inlet for about 5 seconds. Please add a comment in the text on the how much ammonium nitrate (and other semi-volatile species) could have evaporated before sampling. Could this be another reason why nitrate levels were lower for the present study compared to sites in eastern China?
7) I respectfully disagree with the authors’ choice of units for the aerosol mass and number concentrations in the present paper. I understand that previous data from the region was reported for ambient conditions and that the present results are reported for ambient conditions for consistency. It is unfortunate that the prior data from this region were not reported for standard conditions, especially since some sites are very high in altitude. Also, I realize that converting the current data into standard units is somewhat trivial if the ambient conditions are also reported (here sampling temperature was about 23 degrees C and the ambient pressure was not reported and is not readily apparent). However, when working with data sets at pressures significantly different from standard conditions (such as high altitude or aircraft data or global/regional modeling results and comparing the current results to sites at sea level like most listed in Figure 1 and Table S1), it is significantly easier to compare data if it is all reported using standard conditions. Because the site was relatively high in altitude (3295 m a. s. l.), the ambient pressure is roughly 0.67 times sea level pressure, resulting in a correction of a factor of 1.5. Correcting for sampling temperature to standard temperature of 273.15 K will be another factor of 1.08. Please clearly add a sentence (or a two) in the text that mentions the conversion to standard units is roughly a factor of 1.6 (or the average for the ambient conditions), so that the data reported for standard conditions can be quickly estimated if needed.
8) I also respectfully disagree with the authors’ choice of units for the gas phase species. While it may be convenient for aerosol scientists to report gas phase data in micrograms per cubic meter, these units for gas phase species are not commonly used in atmospheric science and gas phase data are virtually always reported as volume mixing ratios (and what does micrograms per cubic meter mean for NOx?). Again, it is difficult to compare the data reported in this paper without recalculating the gas phase data into units of mixing ratio – for the species here “ppbv” is the most convenient. Please convert all reported gas phase data into mixing ratios of ppbv and change them in the figures and tables.

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ED: Publish subject to technical corrections (09 Sep 2015) by Xiaobin Xu

AR by Yele Sun on behalf of the Authors (13 Sep 2015) Author's response Manuscript

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Short summary

A fall field campaign was conducted at a national background site (3295m a.s.l.) over the Tibetan Plateau. The submicron aerosol was dominated by organics (43%) and sulfate (28%). Secondary organic aerosol (SOA) dominated OA (85%), 17% of which being aged biomass burning OA. New particle formation and growth events were frequently observed, with an average particle growth rate of 2.0nm per hour. The important role of organics in particle growth in the Tibetan Plateau was also demonstrated.