Isoprene and monoterpene emissions in south-east Australia: comparison of a multi-layer canopy model with MEGAN  and with atmospheric observations

Emmerson, Kathryn M.; Cope, Martin E.; Galbally, Ian E.; Lee, Sunhee; Nelson, Peter F.

doi:https://doi.org/10.5194/acp-18-7539-2018

Articles | Volume 18, issue 10

https://doi.org/10.5194/acp-18-7539-2018

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

https://doi.org/10.5194/acp-18-7539-2018

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

Articles | Volume 18, issue 10

Research article

|

31 May 2018

Research article |

| 31 May 2018

Isoprene and monoterpene emissions in south-east Australia: comparison of a multi-layer canopy model with MEGAN and with atmospheric observations

Kathryn M. Emmerson, Martin E. Cope, Ian E. Galbally, Sunhee Lee, and Peter F. Nelson

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Final revised paper (published on 31 May 2018)
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Preprint (discussion started on 18 Oct 2017)
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Interactive discussion

Status: closed

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

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RC1: 'Reviewer comments', Anonymous Referee #1, 17 Nov 2017
- AC1: 'Response to reviewer #1', Kathryn Emmerson, 14 Feb 2018
RC2: 'Anonymous review: “Isoprene and monoterpene emissions in Australia: comparison of a multi-layer canopy model with MEGAN and with atmospheric concentration observations”', Anonymous Referee #2, 26 Nov 2017
- AC2: 'Response to reviewer 2', Kathryn Emmerson, 14 Feb 2018
AC3: 'Author comment to the editor', Kathryn Emmerson, 14 Feb 2018

Peer-review completion

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

AR by Kathryn Emmerson on behalf of the Authors (15 Feb 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (28 Feb 2018) by Janne Rinne

RR by Anonymous Referee #1 (27 Mar 2018)

RR by Anonymous Referee #2 (29 Mar 2018)

Suggestions for revision or reasons for rejection

I thank the authors for their thorough response to my (and the first reviewer’s) comments. The textual changes have substantially improved the clarity of the methodology, results and conclusions. While I still have reservations with regard to their justification for the use of ABCGEM study and their over-emphasis of the importance of their conclusions regarding land cover, I am satisfied that the manuscript is now suitable for publication in ACPD.

Specific comments:
I am particularly pleased that the authors have conducted a sensitivity test on the light-dependency of monoterpene emissions from Australian eucalypt ecosystems. The findings of this additional test are well-presented, well-explained and, to my mind, reach a conclusions that does mark a clear step forward in emissions modelling. Importantly this is a finding that is globally applicable and relevant.

Likewise, the extended uncertainty analysis demonstrating the consistency between top-down and bottom-up estimates of the uncertainty in emission rates makes a valuable contribution. As the authors point out, what is now needed is a long-term comprehensive series of atmospheric and leaf-level measurements to further constrain uncertainties.

I thank the authors for the extended description of the various measurement sites and campaigns. I find this makes the comparisons and model evaluations much more meaningful and far easier to follow.

I still feel that the authors place far too much emphasis on their conclusion that modelled landscape scale emissions are critically dependent on the landcover maps used to drive the mode. Regardless of whether or not it is the first time this has been published for Australia it is NOT a novel finding. There is a canon of literature from all world regions (e.g. Arneth et al. (2011; global); Langford et al. (2010; SE Asia), Warneke et al. (2010; US), Huang et al. (2015; US), Zhao et al. (2016; US), Otter et al., 2003; Africa)) to demonstrate precisely that.

The authors state that they have chosen to confront the MEGAN model with ABCGEM because MEGAN in its “default” setting proved to perform poorly over Australia. Emmerson et al. (2016) concluded that the reason for that poor fit was the use of incorrect emission factors but the authors now seem to be arguing that in fact it is a more fundamental problem: that Australia’s unique isolation and environmental conditions have resulted in the evolution of different emissions mechanisms. There is certainly a wealth of evidence that VOC synthesis has evolved independently in numerous lines of vegetation at different times. However, the emissions algorithms in ABCGEM are based on the original Guenther et al (1993) empirical formulations, as are those in MEGAN. This study can not therefore be claimed to be investigating any such fundamental difference in VOC synthesis. The authors need to make this entirely clear.

Finally, I still find the authors to be muddled in their description of emission factors. Until the emission factors in ABCGEM have been scaled up to the landscape scale they are NOT comparable with the gridded emission factors that are used with MEGAN. However, overall I find the discussion of emission factors and emissions much clearer and thank the authors for clarifying their terminology.

Overall, I now feel that this is a robust and substantial study and strongly recommend publication in its present form.

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ED: Publish subject to minor revisions (review by editor) (18 Apr 2018) by Janne Rinne

AR by Kathryn Emmerson on behalf of the Authors (26 Apr 2018) Author's response Manuscript

ED: Publish as is (08 May 2018) by Janne Rinne

AR by Kathryn Emmerson on behalf of the Authors (09 May 2018) Author's response Manuscript

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Short summary

We compare the CSIRO in-house biogenic emissions model (ABCGEM) with the Model of Emissions of Gases and Aerosols from Nature (MEGAN), for eucalypt-rich south-east Australia. Differences in emissions are not only due to the emission factors, but also how these emission factors are processed. ABCGEM assumes monoterpenes are not light dependent, whilst MEGAN does. Comparison with observations suggests that Australian monoterpenes may not be as light dependent as other vegetation globally.