Higher measured than modeled ozone production at increased NO<sub><i>x</i></sub> levels in the Colorado Front Range

Baier, Bianca C.; Brune, William H.; Miller, David O.; Blake, Donald; Long, Russell; Wisthaler, Armin; Cantrell, Christopher; Fried, Alan; Heikes, Brian; Brown, Steven; McDuffie, Erin; Flocke, Frank; Apel, Eric; Kaser, Lisa; Weinheimer, Andrew

doi:https://doi.org/10.5194/acp-17-11273-2017

Articles | Volume 17, issue 18

https://doi.org/10.5194/acp-17-11273-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/acp-17-11273-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 17, issue 18

Research article

|

25 Sep 2017

Research article |

| 25 Sep 2017

Higher measured than modeled ozone production at increased NO_x levels in the Colorado Front Range

Bianca C. Baier, William H. Brune, David O. Miller, Donald Blake, Russell Long, Armin Wisthaler, Christopher Cantrell, Alan Fried, Brian Heikes, Steven Brown, Erin McDuffie, Frank Flocke, Eric Apel, Lisa Kaser, and Andrew Weinheimer

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Final revised paper (published on 25 Sep 2017)
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Preprint (discussion started on 04 Jan 2017)
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Status: closed

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

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RC1: 'Referee's report', Anonymous Referee #2, 18 Jan 2017
- AC2: 'Response to Reviewer #2', Bianca Baier, 19 May 2017
RC2: 'Baier et al.', Anonymous Referee #1, 27 Jan 2017
- AC1: 'Response to Reviewer #1', Bianca Baier, 19 May 2017

Peer-review completion

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

AR by Bianca Baier on behalf of the Authors (23 May 2017) Author's response Manuscript

ED: Referee Nomination & Report Request started (13 Jun 2017) by Frank Keutsch

RR by Anonymous Referee #1 (01 Jul 2017)

RR by Anonymous Referee #2 (07 Jul 2017)

Suggestions for revision or reasons for rejection

Introduction, pg 4, lines 15 – 35: I found this revised section a little misleading. I think this could be rectified if the magnitudes of modelled to measured HO2 (and modelled to measured p(O3)) disagreement are compared in absolute terms. In the Tan et al (2017) study, modelled and measured HO2 agree within uncertainty at 6 ppbv NO. By eye, (but the authors can provide an accurate number) at 6 ppbv NO in this study P(O3) measured is ~20 ppb hr-1 greater than modelled. The Tan et al (2017) study does not support the magnitude of the P(O3) discrepancy reported in this work and this needs to be reflected in the Introduction.

The authors have made some attempts to improve the corrections applied to the raw MOPS data by limiting times when RH was below 70%. It is not obvious from looking at the latest time-series in Figure 1 that the MOPS data coverage presented has reduced. Was this threshold RH already applied before the initial submission?

There is still a lot of uncertainty associated with all the corrections applied, however. The authors state that the negative ozone production rates are ‘roughly correlated with temperature, relative humidity, or actinic flux’. Could the authors provide an equation of the form:

Artificial signal = Temperature × a(±b) + RH × c(±d) + hν × e(±f)

This will provide some confidence in the corrections applied.

Related to this point, the authors discuss the days chosen for the zero measurements: ‘zeros that were taken only on days with diurnal patterns and absolute values of relative humidity that are similar to most MOPS measurements days’. The authors need to be specific here, what do they mean by ‘similar’ and ‘most’? Furthermore, this statement begs the question, how similar was temperature and actinic flux on these days also given the correlation with these parameters too?

It is not clear in Figure S2 which line relates to which RH?

Section 3.3 is much improved from the initial submission, however, a couple of modifications are needed:

Pg 12, line 32: ‘either all of these measurements methods contain similar artifacts..’ this argument does not hold. Why, if this is an instrumental problem rather than missing chemistry does this have to relate to a similar artifact? Rather, the MOPS artificial signal may derive from heterogeneous production of radicals or radical precursors whilst the previous FAGE measurements could be influenced by an RO2 interference. This sentence needs to be modified to reflect this.

The authors argue that the positive excursion in P(O3) is apparent even before the zero correction is applied and use this as evidence that the positive excursion is not an instrumental artefact (pg 12, lines 22 – 27). I do not agree with this reasoning. It may be true that the zero correction is not inducing this positive P(O3) observed in the mronings, but other artifacts, for example, artifacts induced by heterogeneous NO2 reactions in the chamber could be contributing to this signal. The authors mention on Pg 7, line 25 ‘excess HONO of up to five times ambient values was measured in the MOPS chambers’ and that the ‘production mechanism has not been identified’ Really, systematic laboratory studies are needed to determine the absolute magnitude of this heterogeneous HONO production as a function of NOx. Failing that, the authors should at least modify the discussion in section 3.3.1 to reflect the fact that the model measurement discrepancy at high NOx could be caused by a currently unidentified HONO (or radical) production mechanisms in the MOPS that may not necessarily scale with NOx as assumed in section 3.3.1.

Figure 6, Some comment is needed about why P(O3) in the MCM3.3.1 RO2=0.0005x[NOx] scenario is lower (despite [RO2] concentrations being higher) than the base MCM case in the afternoon.

Also the scenario where RO2+NO  HO2 + NO2 is not shown in Figure 6 as indicated in lines 27, 28, pg 16 (unless it is represented by the green dashed line, in which case the legend needs correcting).

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ED: Reconsider after minor revisions (Editor review) (15 Jul 2017) by Frank Keutsch

AR by Bianca Baier on behalf of the Authors (27 Jul 2017) Author's response Manuscript

ED: Publish as is (03 Aug 2017) by Frank Keutsch

AR by Bianca Baier on behalf of the Authors (12 Aug 2017)

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Short summary

Ozone production rates were measured using the Measurement of Ozone Production Sensor (MOPS). Measurements are compared to modeled ozone production rates using two different chemical mechanisms. At high nitric oxide levels, observed rates are higher than those modeled, prompting the need to revisit current model photochemistry. These direct measurements can add to our understanding of the ozone chemistry within air quality models and can be used to guide government regulatory strategies.

Higher measured than modeled ozone production at increased NOx levels in the Colorado Front Range

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Higher measured than modeled ozone production at increased NO_x levels in the Colorado Front Range