PAH concentrations simulated with the AURAMS-PAH chemical transport model over Canada and the USA

Galarneau, E.; Makar, P. A.; Zheng, Q.; Narayan, J.; Zhang, J.; Moran, M. D.; Bari, M. A.; Pathela, S.; Chen, A.; Chlumsky, R.

doi:https://doi.org/10.5194/acp-14-4065-2014

Articles | Volume 14, issue 8

https://doi.org/10.5194/acp-14-4065-2014

© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/acp-14-4065-2014

© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 14, issue 8

Research article

|

23 Apr 2014

Research article |

| 23 Apr 2014

PAH concentrations simulated with the AURAMS-PAH chemical transport model over Canada and the USA

E. Galarneau, P. A. Makar, Q. Zheng, J. Narayan, J. Zhang, M. D. Moran, M. A. Bari, S. Pathela, A. Chen, and R. Chlumsky

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Final revised paper (published on 23 Apr 2014)
Supplement to the final revised paper
Preprint (discussion started on 09 Jul 2013)
Supplement to the preprint

Interactive discussion

Status: closed

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

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- Supplement

RC C5313: 'Review of acp-2013-325', Anonymous Referee #2, 29 Jul 2013
- AC C8547: 'Authors' Response to Referee #2', Elisabeth Galarneau, 28 Oct 2013
RC C7022: 'Interactive comment on “PAH concentrations simulated with the AURAMS-PAH chemical transport model over Canada and the USA” by E. Galarneau et al.', Anonymous Referee #1, 17 Sep 2013
- AC C8546: 'Authors' Response to Referee #1', Elisabeth Galarneau, 28 Oct 2013

Peer-review completion

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

AR by Elisabeth Galarneau on behalf of the Authors (28 Oct 2013) Author's response Manuscript

ED: Referee Nomination & Report Request started (29 Oct 2013) by Jan W. Bottenheim

RR by Anonymous Referee #1 (18 Nov 2013)

B) Suggestions for revision or reasons for rejection

Summary: The authors have addressed some of the points raised, but not all of them. The model may be suitable to simulate exposure near the sources, but not in remote areas, which cover certainly more than half of the domain, at least not for semivolatiles, due to insufficient process resolution (air-surface exchange).
I recommend to reject the paper or insist that the results are limited to non-volatile PAHs (as suggested in the review to the submitted version).

Description of model used:
Sufficient in the revised version

Gas-particle partitioning – discussion of unplausible model results:
The authors refuse to discuss, but plan to address in a subsequent publication.

Air-surface exchange and model evaluation by comparison with observed data / choice of monitoring sites:
The authors maintain that the neglect of air-surface exchange is insignificant as these "parametrizations likely have a minor effect in regions subject to ongoing PAH emissions" and "atmospheric PAH burdens in North America are likely not dominated by air-surface exchange".
However, in model study with air-surface exchange considered it was found for two semivolatile PAHs addressed in the Galarneau et al. study (anthracene and fluoranthene) that volatilization from soil exceeds depositions in summer not only in remote areas of North America (the US West, British Columbia, Ontario), but also in areas certainly influenced by sources (the US Midwest, southern Ontario, California) (Fig. S7b in Lammel et al., 2009). The reason is that the characteristic travel distance from the source in combination with lifetimes in soil lead to burdens in soil, decreasing with distance from source, which turn into secondary emissions and may seasonally exceed the deposition of advected primary and secondary emissions and model will underpredict concentrations at remote sites.
The atmospheric levels of fluoranthene and pyrene, respectively, are expected to drop to 37% and 14% (1/e and 1/e², respectively) within characteristic travel distances from the sources of 160-450 km and 320-900 km, respectively. (These ranges conservatively represent upper estimates as based on the climatological 24-hour mean oxidant level, (0.38-1.24)x106 OH cm-3 within the model domain (Spivakovsky et al.. J. Geophys. Res. 2000), while more PAH is emitted during day-time.)
The authors insist that the spatial resolution (42km) is high enough to reproduce the gradients in urban areas. “As seen in Figure 4, the model performance does not differ much between sites.” However, the sites indicating worst model performance (modelled/measured <0.1), WHI and STJ, are remote sites, unlike most other sites tested.

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RR by Anonymous Referee #3 (08 Dec 2013)

ED: Reconsider after major revisions (24 Dec 2013) by Jan W. Bottenheim

AR by Elisabeth Galarneau on behalf of the Authors (11 Feb 2014)

ED: Referee Nomination & Report Request started (13 Feb 2014) by Jan W. Bottenheim

RR by Anonymous Referee #3 (02 Mar 2014)

ED: Publish as is (03 Mar 2014) by Jan W. Bottenheim

AR by Elisabeth Galarneau on behalf of the Authors (04 Mar 2014)

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