Impact of isoprene and HONO chemistry on ozone and OVOC formation in a semirural South Korean forest

Kim, S.; Kim, S.-Y.; Lee, M.; Shim, H.; Wolfe, G. M.; Guenther, A. B.; He, A.; Hong, Y.; Han, J.

doi:https://doi.org/10.5194/acp-15-4357-2015

Articles | Volume 15, issue 8

https://doi.org/10.5194/acp-15-4357-2015

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

Special issue:

Atmospheric impacts of Eastern Asia megacities

https://doi.org/10.5194/acp-15-4357-2015

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

Articles | Volume 15, issue 8

Research article

|

29 Apr 2015

Research article |

| 29 Apr 2015

Impact of isoprene and HONO chemistry on ozone and OVOC formation in a semirural South Korean forest

S. Kim, S.-Y. Kim, M. Lee, H. Shim, G. M. Wolfe, A. B. Guenther, A. He, Y. Hong, and J. Han

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Final revised paper (published on 29 Apr 2015)
Preprint (discussion started on 24 Jun 2014)

Interactive discussion

Status: closed

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

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SC C5010: 'choice of scenarios and parameter alpha', J.-F. Müller, 17 Jul 2014
RC C5041: 'rural concentrations and air chemistry reactions rather than urban-rural interactions in a South Korean forest', Anonymous Referee #1, 17 Jul 2014
RC C6108: 'comments', Anonymous Referee #2, 21 Aug 2014
AC C7316: 'Responses to the comments', Saewung Kim, 22 Sep 2014

Peer-review completion

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

AR by Saewung Kim on behalf of the Authors (22 Sep 2014) Manuscript

ED: Referee Nomination & Report Request started (22 Sep 2014) by Klaus Schaefer

RR by Anonymous Referee #2 (02 Oct 2014)

RR by Anonymous Referee #1 (09 Oct 2014)

Suggestions for revision or reasons for rejection

Comments to modifications

The presentation of results has considerably improved and at least the online source of the model and the urban data are now presented. Wording is also better but still problematic in parts, particularly towards the end of the manuscript, therefore, I am now more specific in my detailed comments (see below). I still think that the 'urban-rural part' of the title is misleading although this is not a major point since I can follow the argumentation of the authors. Similarly, I agree that the merging of results and discussion is not uncommon for ACP although the chapter gets very long. However, at least the headline should be changed from 'results' into 'results and discussion'.

The diurnal cycle of the monoterpene concentrations and the obvious difference to isoprene concentration is still not explained or sufficiently discussed. I also pity the opinion of the authors that suggested literature is not relevant to discuss while the manuscript still presents discussion parts that seem not to be essential. Spaulding et al. 2003 is still missing in the reference list and uncertainties in the measurements are still not shown. The term KST has to be explained at first appearance (Fig. 1 not 2).

Some more specific comments

Line 116: An 'evolution of thought' cannot be derived from only one previous statement.

Line 125: missing 'at' before low

Line 131: 'for' instead of 'in'

L132: 'regarding' or similar instead of 'in'

L142: replace 'alarming' by 'underlined' or similar

L166-168: not 'Methods'

L252: What specific parameters are listed where?

L278-285: I don't see the context of these lines (delete?)

L298: The MT is not highest during night but in the morning (sunset?) this could hardly be explained by the planetary boundary layer.

L299/300: repetition

L301/302: I don't see how branch enclosure measures that were only done around midday could indicate how the emissions develop throughout the day.

L311: replace 'suppresses' with 'masks' or similar

L313-315: So what? (delete?)

L321/322: Neither done nor shown (delete)

L327-331: Rather introduction than discussion. Is any of the investigated oaks relevant here? (if not delete?)

L334: delete 'observed'

L338: does MEK count as AVOC?

L356/357: More investigations are always required. If this statement is considered important, please specify specifically why and what for!

L372/373: Introduction

L374-378: Repetition and not modeling results (delete)

L381: insert 'simulations with' (or similar) before 'observed'

L383-385: the mechanism is constrained by scenarios? (new wording)

L388: 2.6 what? (new wording!)

L395: 6 (not 5) Scenarios are shown in Fig. 3! (5 are shown in Fig. 3 top row)

L412: delete 'is'

L414: delete 'Most', add 'in the' before 'model'

L419-421: This sentence is unclear and I don't see the logic in it. It also sounds as a conclusion, not a discussion point (delete)

L423: bold letters

L437-439: unclear (new wording!)

L448: replace 'conspicuous' by 'apparent' or similar

L458: R7, not R6

L472-484: This paragraph makes a lengthy statement about relatively well known facts ending in the conclusion that isoprene is important for ozone formation – what has also been shown in previous studies. In my opinion this should be radically shortened or deleted at all.

L498: delete 'evaluation'

L500: If ozone formation is always VOC limited, why is it then obvious to investigate the radical chemistry to determine ozone production – at least in this case? Please refine argumentation.

L504-507: No, this paper doesn't address the difficulties of policy implementation at all (delete or reformulate considerably).

L514/517: 'Most' studies are all presented in 'Sinha et al. 2010'? (check)

L519: replace 'as' by 'are the'

L523: Paragraph end after compounds? Where is the link between the sentences?

L543-545: SOA formation is not discussed previously and is not the topic here. Thus conclusions about this are misplaced (delete).

L547: The summary should be in the abstract (stay with conclusions)

L556: Again, I don't see any indication of aerosol formation from aged pollution in this paper.

L565: replace 'twice' by 'twofold'

L569: What is meant by 'indicate contrary results'?

L572-574: More studies are always required. If this statement is considered important, please specify specifically why and what for!

L582: R7, not R6

L590: What is meant by 'morning and afternoon show a very strong contrast with morning'?

L593-596: No, these results don't indicate that uncertainties in photochemistry propagate policy making processes. It is even quite uncertain if they should. Do you want to argue that NOx should be reduced because then trees would be less damaged by ozone? Since this is a strongly VOC limited regime measures would have to be unrealistically severe. (delete or strongly reword)

Fig. 1: KST not explained. Please give also weather information (at least temperature, possibly radiation and wind speed). Please show uncertainty ranges or explain why this is not possible.

Fig. 2: Put xylene at the top of the panel to match the order of compounds in the figure

Fig. 6: needs better indication of a) and b). Such a differentiation should be applied for figures 3 and 4 too.

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ED: Reconsider after major revisions (09 Oct 2014) by Klaus Schaefer

AR by Saewung Kim on behalf of the Authors (30 Oct 2014) Manuscript

ED: Referee Nomination & Report Request started (31 Oct 2014) by Klaus Schaefer

RR by Anonymous Referee #3 (26 Nov 2014)

RR by Anonymous Referee #4 (06 Dec 2014)

Suggestions for revision or reasons for rejection

This manuscript describes the photochemical box model simulations constrained to observations of ozone precursors to explore radical photochemistry and ozone production regimes at the Taehwa forest site in South Korea. The impact of isoprene chemistry mechanism and elevated concentrations of HONO was studied.

I find that critical comments and recommendation given by the previous two reviewers are often not taken into account by the authors seriously and that the points that the authors noticed important are not adequately discussed even in the latest revised manuscript. The most fatal three points are as follows:

1) Although Dr. Mueller warned that the OH yield of 2.6 is not any more the consensus of the research community and recommended more than 10 times lower value, the authors just continued to use the original value that is outdated. Also, it is nonsense that combination of (1) OH recycle from the isoprene peroxy radical + HO2 reaction and (2) HPALD chemistry is tested (Scenario IV). The two mechanisms are separately proposed in the past to explain high OH levels observed during GABRIEL campaign (likely affected by interference) and therefore the combination should overpredict OH even for the GABRIEL measurements. The interference issue in the used instrument (e.g., Novelli et al., AMT, 2014) also needs to be taken into account seriously.

2) If the authors still believe that such high OH yield takes place, RO2 + HO2 reaction rates, likely dominated by isoprene peroxy radical + HO2 reaction, need to be categorized to "radical recycling" process in section 3.3. The authors seem to have recognized this issue because they mentioned in the latest manuscript (lines 495-497) that "we may need to reconsider R4 as a radical recycling process"; surprisingly however, they continued to follow the conventional classification in the analysis. The logic here is clearly self-inconsistent.

3) The authors used photostationary state analysis for NO and NO2 (line 524 of the latest manuscript) trying to explain observed [NO]/[NO2] ratio that is extraordinary low (<0.1, calculated from [NO]=0.6 ppb and [NO2]= 6 ppb at around 10 KST as read from Figure 1). When I assume that the JNO2 value is about 5 x 10-3 s-1 (for which no observational or simulation information is provided in the manuscript!) and the [O3], [HO2], and [RO2] levels shown in Figure 1 and Table 4, the [NO]/[NO2] ratio can be 0.25 for the morning period, but not as low as 0.1. Only if the JNO2 value is as low as 2 x 10 -3 s-1 (as UV actinic flux is highly blocked by the forest?), the observed low [NO]/[NO2] might be reproduced. The even lower [NO]/[NO2] ratio in the afternoon (around only 0.016, as calculated from [NO]=0.05 ppb and [NO2]=3 ppb at around 14 KST shown in Figure 1) is much more difficult to be reconciled with the photostationary state theory. The authors should have used the equation (labeled as R7, although this is not chemical reaction!) to test their hypothesis given in the lines 526-534 quantitatively. I may suspect that the NO2 measurements suffered from interference from NOz species. The authors at least need to describe which type of converter was used in the NOx measurements. If NO2 measurements are incorrect, all calculation of the radical concentrations and the regime determination may be false. To remove my doubt, the authors need to provide information of J value measurements and their treatment in the model, the type of converter is used for NO2 measurements, and quantitative explanation why the observed [NO]/[NO2] ratios were so low.

Besides the above three points, I still find two more critical issues.
First point is on the judgment criteria of the ozone production regime. The authors cite Tonnesen and Dennis (2000) and used the ratio range (PH2O2/PHNO3) of 0.35 as the border range. However, I only found in Tonnesen and Dennis (2000) that the border lies with the ratio (PH2O2/PHNO3) of 0.06-0.07 in the daytime. The authors need to clarify this first. Also, such value determined for a different site and different season could not be valid for the campaign studied in this manuscript, because of the strong influence from the types of VOCs present in the atmosphere and J values. Especially, I do not understand why the regimes can be determined with the same criteria for scenarios II, IV, and V, where the isoprene chemistry mechanism was severely modified. Clearly different approach (e.g., model sensitivity experiments of ozone production rates on the amount of NOx or VOCs) is recommended.

Second, nighttime isoprene concentration levels as high as 1 ppbv have rarely been reported and thus more explanation should be provided. The cited literatures (Apel et al., 2002; Bryan et al., 2012) reported much lower nighttime levels. The authors need to discuss possibility of interference in the PTR-MS measurements during night and similar artifact in the daytime isoprene measurements.

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RR by Anonymous Referee #2 (09 Dec 2014)

ED: Reconsider after major revisions (09 Dec 2014) by Klaus Schaefer

AR by Saewung Kim on behalf of the Authors (26 Jan 2015) Author's response Manuscript

ED: Referee Nomination & Report Request started (26 Jan 2015) by Klaus Schaefer

RR by Anonymous Referee #4 (11 Feb 2015)

Suggestions for revision or reasons for rejection

The manuscript has been improved mainly by employing up-to-date consensus knowledge of the HOx-isoprene chemistry. However still some revision is necessary:

1. Title: Although isoprene chemistry is heavily studied here, roles of anthropogenic hydrocarbon are almost unstudied. Therefore, "urban-rural interactions govern ... " in the current title is too much. "Impact of isoprene and HONO chemistry on ozone and OVOC formation in a semirural South Korean forest" might be better.

2. My previous request to mention observation or assumption of J values is neglected. Please include some explanation.

3. Now the authors conclude that impact of isoprene chemistry on OH/HO2/RO2 radicals is less important than the impact of the HONO treatment. But still, most description in Introduction is on isoprene chemistry, and HONO is almost unmentioned. More balanced Introduction section is necessary.

4. Line 153. Maybe 2012?

5. How will the possible interference of PANs etc in the NO2 measurement, now mentioned in sections 2.2 and 3.1, affect the discussion on 2P(H2O2)/P(HNO3)? P(HNO3) should be largely affected. Discussion on this point is also critical.

6. line 402. four different model scenarios

7. lines 448-449. In Table 3 the authors discussed that HO2 is slightly increased and RO2 is decreased. Why the RO2+HO2 reaction rates increased here?

8. line 452. Considering relatively high NOx concentrations at TRF, this is surprising …

9. lines 499. For more rural condition at the top of Mt. Tai, China, Kanaya et al. (ACP 2009) mentioned that ozone production is basically NOx limited.

10. line 519. Some more explanation is necessary for the lower P(peroxide)/P(HNO3). Previously in Figure 4, the authors mentioned that P(peroxide) is increased in Scenario 2. Here, the authors mean that P(HNO3) is MORE ENHANCED because of high OH in this scenario, resulting in the LOWER P(peroxide)/P(HNO3)?

11. line 558. Where did the author discuss on the "factor of 2-3" missing OH reactivity for this campaign?

12. line 560, SOA, not VOCs

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RR by Anonymous Referee #2 (25 Feb 2015)

RR by Anonymous Referee #5 (16 Mar 2015)

Suggestions for revision or reasons for rejection

This mnuscript presensted an detailed analysis on radicals levels at a rural site around Seoul based on a pbservational dataset and box models. The observational data on HONO and VOCs is interesting, and gave valuable insight into the HONO cncentration in Kirea. The results gave lend insight into radical recycle. This manuscript shoeld be of interest to ACP readers and would be suitable for publication with minor revisons.
1. Line 170-172. The author used a Thermo 42i TL to observe NO/NOx. I am afraid that NO2 measurements systematically overestimate the true value because of interferences of these compounds especially when Sampling photochemically aged air masses. THe Mo converter could other oxidized nitrogen compounds such as peroxyacetyl nitrate and nitric acid are also partly converted to NO. The author should discuss the uncertaities on results caused by NO/NO2 obervations.
2. The author mentioned that TRF is not directly influenced by Seoul pollution plume by comparing NO2 concentrations at two sites. This is not enough. In some cases, although NO2 is not tranported, other chemical compounds like PAN and nitrate are likely tranported a longer distance. The author had better examine the wind direction and velocity.If the manuscript can provide TRF is not located in the downwinded site of Seoul bt prevailed winds, the statement willl be more evident.
3. Previous studies found that he Heterogeneous chemistry on HONO and HNO3 is important on NOx and O3 chemistry. In particular, radicals like OH and HO2 are mostly affected by O3 and NOx. Thus, discussion on Heterogenous chemistry should be discussed.
4. Page 396 . "is about 40 times" should be "are about 40 times".
5. Line 389 "the impacts to" should be "the impacts on"

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ED: Reconsider after minor revisions (Editor review) (17 Mar 2015) by Klaus Schaefer

AR by Saewung Kim on behalf of the Authors (27 Mar 2015) Manuscript

ED: Publish as is (27 Mar 2015) by Klaus Schaefer

AR by Saewung Kim on behalf of the Authors (02 Apr 2015)