Emissions of biogenic volatile organic compounds and subsequent formation of secondary organic aerosols in a <I>Larix kaempferi</I> forest

Mochizuki, T.; Miyazaki, Y.; Ono, K.; Wada, R.; Takahashi, Y.; Saigusa, N.; Kawamura, K.; Tani, A.

doi:https://doi.org/10.5194/acp-15-12029-2015

Articles | Volume 15, issue 20

https://doi.org/10.5194/acp-15-12029-2015

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

Special issue:

Integrated Land Ecosystem-Atmosphere Processes Study (iLEAPS)...

https://doi.org/10.5194/acp-15-12029-2015

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

Articles | Volume 15, issue 20

Research article

|

29 Oct 2015

Research article |

| 29 Oct 2015

Emissions of biogenic volatile organic compounds and subsequent formation of secondary organic aerosols in a Larix kaempferi forest

T. Mochizuki, Y. Miyazaki, K. Ono, R. Wada, Y. Takahashi, N. Saigusa, K. Kawamura, and A. Tani

Download

Final revised paper (published on 29 Oct 2015)
Preprint (discussion started on 14 Apr 2015)

Interactive discussion

Status: closed

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

- Printer-friendly version

- Supplement

RC C2566: 'review', Anonymous Referee #1, 14 May 2015
- AC C6074: 'Response to Referee#1', Yuzo Miyazaki, 20 Aug 2015
RC C3828: 'Review of Mochizuki et al.', Anonymous Referee #2, 19 Jun 2015
- AC C6075: 'Response to Referee#2', Yuzo Miyazaki, 20 Aug 2015

Peer-review completion

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

AR by Yuzo Miyazaki on behalf of the Authors (20 Aug 2015) Author's response Manuscript

ED: Referee Nomination & Report Request started (20 Aug 2015) by Alex B. Guenther

RR by Anonymous Referee #2 (30 Aug 2015)

Suggestions for revision or reasons for rejection

Further Comments:

Before I can recommend publication of this article, there are still some remaining issues that the authors need to further resolve.

1.) TSP sampling: I understand now that the authors sampled with TSP due to previously seeing some BSOA tracers in the coarse mode. The authors use the word "some" to quantify this. How much have you seen previously in the coarse mode? I suspect this is very small fraction of the total as most of the biogenic SOA (like from isoprene-derived oxidation products) should reside in the fine aerosol mode based on the fact that sulfate is also predominant there and provides the necessary sites for heterogeneous chemical reactions.

It is good to see the authors noted the potential of positive and negative artifacts. I want to stress, I'm not a big fan of TSP sampling for SOA tracers, especially if the filter isn't covered, etc. It has been my experience in the past that TSP samplers don't do a lot to ensure debris, dust from work area, etc. deposit onto the filter. Also, it has been my experience the aerosol is not well protected. I don't mean to nit-pick on this issue, but just pointing out that I think PM10 or PM2.5 samplers in my experience do a better job in protecting the integrity of the aerosol sample. I'm certainly not saying that the PM10 and PM2.5 samplers are the best, as they have their problems due to the positive and negative artifacts that the authors have now discussed and added to the manuscript.

2.) Compounds used for quantification of BSOA tracers: The description is much improved now as it is clear how this was done. I still think the authors need to add a cautionary note in the discussion that the absolute concentrations are still tentative due to the use of surrogate standards.

3.) Determination of aerosol pH from water extraction of quartz filters: Although the authors clearly had good intentions to address my original suggestion to estimate aerosol pH, extracting filters in water to estimate aerosol pH is not appropriate as the pH of the extract solution doesn't represent the "true" aerosol pH. The aerosol pH is only representative of the aqueous layer on the inorganic/organic mixed aerosol. The best way to estimate the "true" aerosol pH is by using an inorganic thermodynamic model, such as ISORROPIA-II (Fountoukis and Nenes, 2007) or E-AIM (see papers by Wexler and Clegg). The groups at GA Tech have had some recent papers discussing this important issue in ACP (Guo et al., 2015; Hennigan et al., 2015). Don't the authors have aerosol sulfate, nitrate, and ammonium data at least from their measurements? In the ideal case, they might also have gaseous ammonia data to better constrain the model estimate. If they don't, then it might make sense as to why they extracted the filters to address this previous comment I raised in my last review. The authors should note that work from the southeastern U.S. has shown at two different sites that aerosol pH is acidic (pH <2) but doesn't vary much during summertime conditions, and thus, doesn't seem to be the controlling variable due to the lack of variation in this parameter (Xu et al. 2015, PNAS; Budisulistiorini et al., 2015, ACP). I wonder if you would find the same thing if the aerosol pH is estimated using one of these thermodynamic models?

4.) Other GC/MS tracers for isoprene SOA:

Did the authors not observe the known C5-alkene triols from isoprene oxidation (or really from reactive uptake of IEPOX) (Wang et al., 2005, Rapid Communications in Mass Spectrometry; Lin et al., 2012, ES&T)? These compounds should be seen by GC/MS with prior trimethylsillylation (as they use here) and are typically as abundant as the 2-methyltetrols. You can easily check the data for the C5-alkene triols by using the extracted ion chromatogram (EIC) of m/z 231. I'm assuming you saw no dimers of IEPOX previously seen by Surratt et al. (2006, J. Phys. Chem. A) or Lin et al. (2012, ES&T) using the EIC of m/z 335?

I should point out if you don't see the C5-alkene triols that is kind of interesting, as a recent paper by Riva et al. (2015, Atmos. Environ.) showed that isoprene ozonolysis in the presence of acidic sulfate aerosol only produced the 2-methyltetrols but no C5-alkene triols were produced, suggesting an alternative mechanism from IEPOX uptake chemistry that leads to 2-methyltetrol formation.

5.) Filter sampling size: Since the authors state clearly "that the goal of this study is to investigate controlling factors of BSOA formation from BVOC in a forest environment located near anthropogenic sources," I must state that I'm still cautious by the limited filter sampling used in this study. The paper kind of reads that this research activity was an afterthought to the flux measurements. Since the filter data is used for the PMF analyses, it seems the PMF results can only be interpreted with extreme caution. It would have been better of course if the authors had considered conducting longer sampling of filters, especially if you wanted to capture more variability in biogenic only vs. biogenic influenced by anthropogenic pollutants. Although the authors now argue this is the right time of year for biogenic emissions based on previous measurements, how do you conclude 5 days of sampling is enough for measuring the trends of BSOA tracers versus other co-located data? I realize the authors cannot go back and make more measurements, but I think the authors must acknowledge that extreme caution must be used with how to interpret the PMF results. I noted the other reviewer shared some of my concerns with the PMF.

Hide

ED: Reconsider after major revisions (06 Sep 2015) by Alex B. Guenther

AR by Yuzo Miyazaki on behalf of the Authors (25 Sep 2015) Author's response Manuscript

ED: Referee Nomination & Report Request started (28 Sep 2015) by Alex B. Guenther

RR by Anonymous Referee #2 (09 Oct 2015)

ED: Publish as is (11 Oct 2015) by Alex B. Guenther

Short summary

Simultaneous measurements of concentrations and above-canopy fluxes of isoprene and α-pinene in a forest, along with their oxidation products in aerosols, suggest that the inflow of anthropogenic precursors/aerosols enhanced the formation of both isoprene- and α-pinene-derived secondary organic aerosol (SOA) within the forest canopy even when the flux was low. We also emphasize the role of vegetation/soils near the forest floor as important sources of isoprene and α-pinene in the forest.