Measurement report: Source characteristics of water-soluble organic carbon in PM<sub>2.5</sub> at two sites in Japan, as assessed by long-term observation and stable carbon isotope ratio

Suto, Nana; Kawashima, Hiroto

doi:https://doi.org/10.5194/acp-21-11815-2021

Articles | Volume 21, issue 15

https://doi.org/10.5194/acp-21-11815-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-21-11815-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 21, issue 15

Measurement report

|

09 Aug 2021

Measurement report |

| 09 Aug 2021

Measurement report: Source characteristics of water-soluble organic carbon in PM_2.5 at two sites in Japan, as assessed by long-term observation and stable carbon isotope ratio

Nana Suto and Hiroto Kawashima

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Final revised paper (published on 09 Aug 2021)
Supplement to the final revised paper
Preprint (discussion started on 16 Nov 2020)
Supplement to the preprint

Interactive discussion

Status: closed

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

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RC1: 'Rewiew on: Measurement report: Source characteristics of water-soluble organic carbon in PM2.5 at two sites in Japan, as assessed by long-term observation and stable carbon isotope ratio', Anonymous Referee #1, 10 Dec 2020
- AC1: 'Reply on RC1', Nana Suto, 23 Feb 2021
RC2: 'Review of the manuscript entitled “Measurement report: Source characteristics of water-soluble organic carbon in PM2.5 at two sites in Japan, as assessed by long-term observation and stable carbon isotope ratio” by N. Suto and H. Kawashima', Andrius Garbaras, 02 Jan 2021
- AC2: 'Reply on RC2', Nana Suto, 23 Feb 2021

Peer-review completion

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

AR by Nana Suto on behalf of the Authors (23 Feb 2021) Author's response Author's tracked changes Manuscript

ED: Reconsider after major revisions (01 Mar 2021) by Rupert Holzinger

ED: Referee Nomination & Report Request started (02 Mar 2021) by Rupert Holzinger

RR by Anonymous Referee #1 (16 Mar 2021)

Suggestions for revision or reasons for rejection

2. Review on:

Measurement report: Source characteristics of water-soluble organic carbon in PM2.5 at two sites in Japan, as assessed by long-term observation and stable carbon isotope ratio by Suto and Kawashima

The revised manuscript shows that the authors considered only some of the recommendations suggested by the reviewers. Therefore, there are still open points to be reconsidered.

The major criticism was unfortunately not reviewed: since only TC isotopic ratios of WSOC and whole aerosol particles were measured, comparison with compound specific d13C are superfluous (to illustrate this, two extremes should be considered, i.e. 3.8% levoglucosan originates from the combustion of corn plant only (d13C=-12 permille) or a C3 wood only (mean d13C=-24 permille). Keeping the rest unchanged, a difference in the bulk d13C of 0.46 permille would result, which is in the uncertainty range of some compound specific analyses). The same is valid for process examination. One of prerequisites to employ mass balance calculations for single mixture components /photo chemical decay is to possess their emissions d13C and the reaction specific KIE. Even then, the complexity of atmospheric processing cannot be solved by just adding up some numbers.

Yet, there are numerous ambient studies on WSOC/TC isotope ratios (see Gensch et al. IJMS2014 and references therein), describing ranges for these compound classes. A sound comparison gives first information on sources. The authors claim that: ‘When C3 plants are burned in the laboratory, there is no significant δ13C difference between the produced particles and original C3 plants’. Still, isn’t sounder to compare the measurements with WSOC/TC d13C in combustion aerosol particles and not in plant tissues (whose δ13C values are −34 to −24‰ for C3 plants and −19 to −6‰ for C4 plants, respectively (Smith and Epstein, 1971) and not −32 to −20‰ for C3 plants and −17 to −9‰ for C4 plants, as given in the present manuscript), since this information already exists?

1) To get some additional information from this impressive dataset, I recommend to the authors to use the existing isotopic tools, such as combining isotope ratios with concentration data (remote sources for Yurihonjo, higher contribution of local/regional emissions to the samples for Tsukuba?). The authors claim in Lines 275-279: ‘From February to April 2019, d13CWSOC became heavier with increasing WSOC concentrations (Fig. 1b and Fig. 275 2b). Although C4 plants such as corn and grass showed heavy d13C, there was no evidence of burning of C4 plants around during this period. The heavy d13CWSOC during this period cannot be explained only by the effect of biomass burning. Aerosol photochemical aging during long-range transport selectively enriches the 13C content in organic aerosols, leading to heavier d13C values in the remaining aerosol’. A simultaneous increase in concentration and d13C is rather an indication for heavy sources than aging... especially during periods of low photo chemical activity.
2) To either prove or reject this hypothesis, the authors should at least roughly (HYSPLIT?) determine the origin of the air masses. In the lines 282-284 the authors state: ‘Uranishi et al. (2020) concluded that biomass burning in northeast China was transported in Akita prefecture regions of Japan in February and March 2019 from Community Multiscale Air Quality model results’. Noticeably here, China’s north-eastern part is belonging to the so called ‘corn belt’. As a result of this farming type, it is expected that local heating with corn briquettes and traditional cooking using corn cobs strongly contribute to the aerosol burden. Subsequently, due to long-range transport, this would contribute to the investigated samples, leading to an increase in d13C.

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RR by Andrius Garbaras (19 Mar 2021)

ED: Reconsider after major revisions (19 Mar 2021) by Rupert Holzinger

AR by Nana Suto on behalf of the Authors (30 May 2021) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (08 Jun 2021) by Rupert Holzinger

RR by Anonymous Referee #1 (22 Jun 2021)

ED: Publish subject to minor revisions (review by editor) (22 Jun 2021) by Rupert Holzinger

AR by Nana Suto on behalf of the Authors (28 Jun 2021) Author's response Author's tracked changes Manuscript

ED: Publish as is (29 Jun 2021) by Rupert Holzinger

AR by Nana Suto on behalf of the Authors (01 Jul 2021) Manuscript

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Short summary

The sources and seasonal trends of water-soluble organic carbon (WSOC) in PM_2.5 on long-term trends at two sites in Japan are investigated by carbon isotope ratio (δ¹³C) of WSOC. At the rural site, the δ¹³C of WSOC from autumn to spring was concluded to reflect mainly the biomass burning of rice straw. The heaviest δ¹³C of WSOC from February to April 2019 might reflect long-range transport of particles resulting from the overseas burning of C₄ plants such as corn.