Sensitivity of biogenic volatile organic compound emissions to leaf area index and land cover in Beijing

Wang, Hui; Wu, Qizhong; Liu, Hongjun; Wang, Yuanlin; Cheng, Huaqiong; Wang, Rongrong; Wang, Lanning; Xiao, Han; Yang, Xiaochun

doi:https://doi.org/10.5194/acp-18-9583-2018

Articles | Volume 18, issue 13

https://doi.org/10.5194/acp-18-9583-2018

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

https://doi.org/10.5194/acp-18-9583-2018

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

Articles | Volume 18, issue 13

Research article

|

09 Jul 2018

Research article |

| 09 Jul 2018

Sensitivity of biogenic volatile organic compound emissions to leaf area index and land cover in Beijing

Hui Wang, Qizhong Wu, Hongjun Liu, Yuanlin Wang, Huaqiong Cheng, Rongrong Wang, Lanning Wang, Han Xiao, and Xiaochun Yang

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Final revised paper (published on 09 Jul 2018)
Supplement to the final revised paper
Preprint (discussion started on 15 Dec 2017)

Interactive discussion

Status: closed

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

- Printer-friendly version

- Supplement

RC1: 'review of MS acp-2017-945', Anonymous Referee #2, 21 Dec 2017
- AC2: 'Response to Referee #2', Qizhong Wu, 24 Mar 2018
RC2: 'Review of Beijing BVOC and landcover study', Anonymous Referee #1, 07 Jan 2018
- AC1: 'Response to Referee #1', Qizhong Wu, 24 Mar 2018

Peer-review completion

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

AR by Qizhong Wu on behalf of the Authors (28 Mar 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (20 Apr 2018) by Frank Keutsch

RR by Anonymous Referee #1 (25 Apr 2018)

RR by Anonymous Referee #2 (03 May 2018)

Suggestions for revision or reasons for rejection

I recognized that the authors made some efforts to improve the presentation of their results, and they now include more details regarding used datasets and their modeling approach. These are helpful.

I still have several major concerns as follows:

1. The authors tried really hard to dig some trend in BVOC emissions during 1998-2013 based on information in Table 6. I do not see a clear increasing trend from the contents in Table 6. I am not convinced that results from these independent studies are directly comparable to produce a trend estimate. This is because these studies used different approaches and/or focused on different areas, and uncertainty of BVOC emissions from this study is unknown (also see my major concern 4 regarding impact from WRF modeling and evaluation). The authors argue that the increasing forest cover contributed to an increase in BVOC emissions, but they do not discuss the impact of meteorology and climate on BVOC emissions during this period. Does a growing forest cover decrease air temperature, which would compensate the emission changes due to the increase in source area and intensity?
2. The authors state that the BVOC estimates represent year 2013. The WRF fields and LAI data are based on 2013, but three of the five experiments used FROM land cover, which is based on year 2010. So please use more accurate language about the year your BVOC emissions represent.
3. The authors should be careful when drawing conclusions that BVOC emissions are insensitive to LAI but sensitive to PFT. Based on my observation, the three LAI products over forest areas differed by ~1.0 in maximum in warm seasons, when the absolute values are 3-5. The spatial patterns of the LAI from three products look consistent as well. The relative differences among PFT data are much larger according to Figure 6. Is the smaller sensitivity to used LAI products (than to PFT products) due to the smaller discrepancy among used LAI products? Can the absolute sensitivities be normalized by LAI or PFT discrepancies?
4. WRF simulations: I wonder why the authors evaluated WRF T2 using hourly observations (Table 3 in author response file) but did not want to include those results in the revised manuscript. There are some differences between those results in that Table and current Table 2. In fact, the current presentation of WRF evaluation is not satisfactory. Specifically,
1) All evaluation statistics are reported for the whole year whereas the BVOC emissions are presented month by month, and an obvious seasonal cycle is seen from the MEGAN BVOC emissions. A clearer way to present your model performance is to show time series plots of the statistical metrics.
2) The authors speculate that the largest cold biases are due to unrealistic land use data in WRF, why don’t you show clearly how WRF land use input looks like over the Beijing area? And why not try to correct them before running WRF? Are there other factors that could contribute to model biases (e.g., FNL, physics, terrain representation, vertical resolution)?
3) The authors should consider adding discussions on how these T2 biases may have introduced uncertainty to their BVOC estimates (e.g., adding a sensitivity run, or cite previous studies on these topics suitably). How does this uncertainty affect their conclusions on BVOC emission trends?
4) Radiation evaluation is only available at Beijing station, where BVOC emissions are low. Not quite useful information.

Line-by-line
P1:
Abstract:
L13-14: “Forest coverage rose from 20.6% to 35.8% from 1998 to 2013 in Beijing according to the National Forest Resource Survey (NFRS).” I suggest to write a concise sentence to emphasize accurate representations of land cover for recent years is important to estimating biogenic emissions and addressing air quality issues.
L21: what is the “baseline” calculation? There is no prior definition in abstract for this.
L22: delete “the” before “isoprene”
L25: “The different PFT inputs strongly influenced the spatial distribution of BVOC emissions, which is determined by the spatial distribution of PFTs.” ->consider shortening it.

P2:
L24: why is mountain mentioned here? Perhaps the authors meant the terrain influences on meteorology that drives BVOC emissions? If so, say that clearly.
L25: “it is necessary to investigate and evaluate the impact of biogenic sources on local air pollution.” -> needs to be reworded. You are not quantitatively evaluating BVOC impacts on air pollution in this study; you only produce BVOC emissions for future evaluations of their impact on air quality.

P5:
L7: clearly say 31 layers included 4 layers of soil from the Noah land surface model. In most publications, WRF model layer does not include soil layers.
L20-23: Causes of these negative biases are not well explained. See also my major comment 4.
Sect 2.2.2: Some information on the temporal frequency of these PFT and LAI products is necessary. I didn’t notice a little information until the results section about the temporal frequencies of some of these LAI products.

P6:
L5: consider a different word than “regarded”
L9: spell out “TM”, also for the “ETM” in P11

P9:
L5: “Additionally, the emissions differ more between experiments in summer than in winter, indicating that the emission estimates for summer are more uncertain than those for winter.” It is not surprising because summertime emissions are high. Be clear that you refer to the absolute values rather than a normalized metric by absolute emission amounts.
L9-11: starting from “As shown in…”, something is messed up. These are not complete sentences.

Finally, the authors concluded that the use of cross-walking table is important (in abstract and conclusion). Why are related results only be shown in the supplement?

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ED: Reconsider after major revisions (07 May 2018) by Frank Keutsch

AR by Qizhong Wu on behalf of the Authors (17 May 2018) Manuscript

ED: Referee Nomination & Report Request started (18 May 2018) by Frank Keutsch

RR by Anonymous Referee #2 (19 May 2018)

Suggestions for revision or reasons for rejection

The authors quickly made some changes according to my comments. I find the responses to my line-by-line comments are generally satisfactory. To address my major concerns, the authors added additional figures showing time series of temperature and radiation at the Beijing station. They also included detailed discussions or caveats. I find some of these changes can be further improved.

One of the major limitations of this paper is that the calculated BVOC emissions are not evaluated by ANY sort of observations or observation-constrained emission estimates. I understand that flux measurements may not be available and making top-down estimates from satellites would be very challenging for this region.

I also understand that this paper concentrates on LAI and PFT, and perhaps that is why the analysis on WRF performance is not quite emphasized. However, as the authors recognized, the WRF performance is important to BVOC calculations. One way to improve your WRF story is to consider reporting temperature and radiation (absolute values from the model) at more sites, or showing the data in maps by season, even though radiation can only be evaluated carefully at the Beijing station. This would allow the readers to discern if they are reasonable, or determine ranges of BVOC emissions based on their own met data and the information given from this paper.

The authors moved cross-walking table related material to the main text, which is helpful. They state in the Abstract that “Adopting the “maximum biomass” table made the CCI-LC relatively consistent with the other two LC products, such that the estimates of BVOC emissions in the Beijing region by the three LC products consistently fell within the range of 28.5–30.5 Gg for isoprene…..”. Similar statements appear in the main text too. Again, I think the authors should be careful asserting that calculations within the range of 28.5–30.5 Gg for isoprene etc are correct/desirable, due to the lack of evaluation on your BVOC emissions.

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ED: Publish subject to minor revisions (review by editor) (05 Jun 2018) by Frank Keutsch

AR by Qizhong Wu on behalf of the Authors (14 Jun 2018)

ED: Publish subject to technical corrections (21 Jun 2018) by Frank Keutsch

Dear authors,

thank you for your detailed response to the reviewer questions and regions to the manuscript.

The manuscript is ready for publication after some technical comments I have for the manuscript.

1. Abstract lin 19. It may be helpful to define PFT before using the acronym.

2. Page 5 line 19: It should be "As shown" not "As showed"

3. Page 5 line 22: Please add "the" between "and" and "simulation"

4. Page 5 line 23. Please change "And the" to "The"

5. Page 5 line 24: I think "exits" should be "exhibits"

6. Page 5 line 26: I think it should be "detailed" not "detail"

7. Page 5 line 27: I suggest deleting "for checking"

8. Page 5 line 30: I suggest changing "where" to "which"

9. Page 6 line 1: I suggest changing "the WRF didn't" to "WRF did not"

10. Page 6 line 2: Please change "And the" to "The"

11. Page 6 line 3: I think it should be "relatively" not "relative"

12. Page 6 line 3: Please change "rural region; thereby" to "the rural region; therefore"

13. Page 6 line 22: Please change "changed" to "change"

14. Page 6 line 22: Please change "were used" to "used"

15. Page 7 line 16: Please change "diverse" to "diversity of"

16. page 10 line 10: Pleas change "oxides of isoprene" to "isoprene oxidation products"

17. P. 15 line 16: Please change "the regional" to "a regional"

18. Please consider adding a comment that it would also be useful to have measurements that could help constrain the model results. One of the reviewers emphasized this as a weakness of the paper. As you have no measurements this is fine, but it would be helpful to point out that these would be very valuable.

Please do not hesitate to contact me if you have any questions.

Best Regards,

Frank Keutsch

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AR by Qizhong Wu on behalf of the Authors (25 Jun 2018) Manuscript

Short summary

The Beijing area has suffered from severe air quality pollution in recent years, including ozone pollution in summer. BVOC emissions play a non-negligible role in air quality and climate. Since the forest cover rate increased from 20.6 % to 35.8 % during 1998–2013 in Beijing, we presented a new estimation of local BVOC emissions in a current scenario based on the latest emission model MEGAN v2.1 and also adopted diverse input datasets for the sensitivities of the model and results.