the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
25 Jan 2021
25 Jan 2021
Central role of nitric oxide in ozone production in the upper tropical troposphere over the Atlantic Ocean and West Africa
- 1Atmospheric Chemistry Department, Max Planck Institute for Chemistry, Mainz, Germany
- 2Institute of Energy and Climate Research, IEK-8: Troposphere, Forschungszentrum Jülich GmbH, Jülich, Germany
- 3Karlsruhe Institute of Technology, Karlsruhe, Germany
- 4Earth System Physics section, The Abdus Salam International Centre for Theoretical Physics, Trieste, Italy
- 5Flight Experiments, German Aerospace Center (DLR), Oberpfaffenhofen, Germany
- 6Climate and Atmosphere Research Center, The Cyprus Institute, Nicosia, Cyprus
- 1Atmospheric Chemistry Department, Max Planck Institute for Chemistry, Mainz, Germany
- 2Institute of Energy and Climate Research, IEK-8: Troposphere, Forschungszentrum Jülich GmbH, Jülich, Germany
- 3Karlsruhe Institute of Technology, Karlsruhe, Germany
- 4Earth System Physics section, The Abdus Salam International Centre for Theoretical Physics, Trieste, Italy
- 5Flight Experiments, German Aerospace Center (DLR), Oberpfaffenhofen, Germany
- 6Climate and Atmosphere Research Center, The Cyprus Institute, Nicosia, Cyprus
Abstract. Mechanisms of tropospheric ozone (O3) formation are generally well understood. However, studies reporting on net ozone production rates (NOPRs) directly derived from in-situ observations are challenging, and are sparse in number. To analyze the role of nitric oxide (NO) in net ozone production in the upper tropical troposphere above the Atlantic Ocean and the West African continent, we present in situ trace gas observations obtained during the CAFE-Africa (Chemistry of the Atmosphere: Field Experiment in Africa) campaign in August and September 2018. The vertical profile of in situ measured NO along the flight tracks reveals lowest NO mixing ratios of less than 20 pptv between 2 and 8 km altitude and highest mixing ratios of 0.15–0.2 ppbv above 12 km altitude. Spatial distribution of tropospheric NO above 12 km altitude shows that the sporadically enhanced local mixing ratios (> 0.4 ppbv) occur over the West African continent, which we attribute to episodic lightning events. Measured O3 shows little variability in mixing ratios at 60–70 ppbv, with slightly decreasing and increasing tendencies towards the boundary layer and stratosphere, respectively. Concurrent measurements of CO, CH4, OH and HO2 and H2O enable calculations of NOPRs along the flight tracks and reveal net ozone destruction at −0.6 to −0.2 ppbv h−1 below 6 km altitude and balance of production and destruction around 7–8 km altitude. We report vertical average NOPRs of 0.2–0.4 ppbv h−1 above 12 km altitude with NOPRs occasionally larger than 0.5 ppbv h−1 over West Africa coincident with enhanced NO. We compare the observational results to simulated data retrieved from the general circulation ECHAM/MESSy Atmospheric Chemistry (EMAC) model. Although the comparison of mean vertical profiles of NO and O3 indicates good agreement, local deviations between measured and modelled NO are substantial. The vertical tendencies in NOPRs calculated from simulated data largely reproduce those from in situ experimental data. However, the simulation results do not agree well with NOPRs over the West African continent. Both measurements and simulations indicate that ozone formation in the upper tropical troposphere is NOx-limited.
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Ivan Tadic et al.
Status: closed
-
CC1: 'Comment on acp-2021-52, ozone measurement technique', Florian Obersteiner, 29 Jan 2021
concerning the measurement techniques, I'd like to add the info that the chemiluminescence data is calibrated by the data from the UV photometer.
So on p.6, we should change l.169 to read as "O3 was quantified with a chemiluminescence detector calibrated by a UV photometer (Fast AIRborne Ozone Instrument; [...]"
...and in table 1 (p.7, l.184ff), in the "Technique / method" column, that would be a change to "UV photometry / chemiluminescence".
Thanks to Andreas Zahn for pointing me to info missing. The reference Zahn et al. 2012 only addresses the chemiluminescence detector and not the whole FAIRO instrument.
- AC1: 'Reply on CC1', Ivan Tadic, 08 Feb 2021
-
RC1: 'Comment on acp-2021-52', Anonymous Referee #1, 08 Mar 2021
The manuscript presents original and valuable experimental results accompanied by global model calculations. Furthermore, it is generally well written and presented. I suggest acceptance of the manuscript for publication, but I have a few minor comments to be considered before the final acceptance.
Comments
1) line 35: The wording "NOx is a toxic gas" sounds rather odd as NOx is not a single gas. To avoid misunderstandings the wording could be revised.
2) line 41: The sentence needs revision.
3) line 84: You may also add some earlier references on NOx-VOC sensitivity of ozone production by Sillman.
3) lines 85-86: Please add a reference for the lifetime of NOx.
4) There are a number of NOPR studies based on in situ HOx or ROx measurements by aircraft or at high altitude stations which could be also considered e,g, Cantrell et al., 1996, Zanis et al., 2000, Cantrell et al. (2003a, Ren et al. (2008), Olson et al. (2012).
5) line 211: Should rather be "is practically one or unit" instead of unity.
6) line 211: Should be Tadic et al. (2017).
7) line 235: You may also add some earlier references for the calculation of net ozone production (e.g. Lin et al., 1988).
8) lines 242-243: You may add a reference for the selection of the 100 ppbv criterion for stratospheric ozone. For example, see Prather et al., 2011. Other model intercomparison studies generally utilized a chemical tropopause defined at the 150 ppbv (Young et al., 2013).
9) lines 251-253: The attribution of high NOx above 12 km to lightning NOx rather than NOx rich stratospheric air is rather speculative, unless if there are some indications from the model results or references for that. Mind also the simultaneous relatively smooth increase of both NO and O3 (as you also mention in page 10) which may point influence of stratospheric air.
10) line 264: At around 6 km it seems that there is an ozone layer of possible stratospheric origin. You may check this with relevant model diagnostics (e.g. specific humidity, potential vorticity or O3S if it is available from the simulation).
11) lines 280-281: This does not necessarily mean that you totally exclude the influence of mixing with air of stratospheric origin.
12) line 308: “ …is shown..” should be deleted.
13) line 368: Although the effect of humidity can be implied from factor α of Eq.4 maybe it is also interesting adding in the supplementary material the observed and simulated specific humidity values.
14) line 379: Should rather be : “ ... is from a factor of 2-3 (below 3 km altitude) to a factor of 10 (above 12 km altitude) stronger ... “
15) Figure 7 is interesting showing the NO dependence of NORP as well as the ozone compensation point (the NO level at which NORP is roughly zero). One possibly limitation is the fact that the aggregated bins correspond to different atmospheric layers with different atmospheric characteristics which can possibly induce the spiky signal in the figure.
16) line 441: You may also take into consideration the ozone compensation point which was derived in previous experimental studies in the free troposphere and which agrees well with these values (see e.g. Zanis et al., JGR, 2000).
- AC2: 'Reply on RC1', Ivan Tadic, 17 Mar 2021
- RC2: 'Comment on acp-2021-52', Anonymous Referee #2, 23 Mar 2021
Status: closed
-
CC1: 'Comment on acp-2021-52, ozone measurement technique', Florian Obersteiner, 29 Jan 2021
concerning the measurement techniques, I'd like to add the info that the chemiluminescence data is calibrated by the data from the UV photometer.
So on p.6, we should change l.169 to read as "O3 was quantified with a chemiluminescence detector calibrated by a UV photometer (Fast AIRborne Ozone Instrument; [...]"
...and in table 1 (p.7, l.184ff), in the "Technique / method" column, that would be a change to "UV photometry / chemiluminescence".
Thanks to Andreas Zahn for pointing me to info missing. The reference Zahn et al. 2012 only addresses the chemiluminescence detector and not the whole FAIRO instrument.
- AC1: 'Reply on CC1', Ivan Tadic, 08 Feb 2021
-
RC1: 'Comment on acp-2021-52', Anonymous Referee #1, 08 Mar 2021
The manuscript presents original and valuable experimental results accompanied by global model calculations. Furthermore, it is generally well written and presented. I suggest acceptance of the manuscript for publication, but I have a few minor comments to be considered before the final acceptance.
Comments
1) line 35: The wording "NOx is a toxic gas" sounds rather odd as NOx is not a single gas. To avoid misunderstandings the wording could be revised.
2) line 41: The sentence needs revision.
3) line 84: You may also add some earlier references on NOx-VOC sensitivity of ozone production by Sillman.
3) lines 85-86: Please add a reference for the lifetime of NOx.
4) There are a number of NOPR studies based on in situ HOx or ROx measurements by aircraft or at high altitude stations which could be also considered e,g, Cantrell et al., 1996, Zanis et al., 2000, Cantrell et al. (2003a, Ren et al. (2008), Olson et al. (2012).
5) line 211: Should rather be "is practically one or unit" instead of unity.
6) line 211: Should be Tadic et al. (2017).
7) line 235: You may also add some earlier references for the calculation of net ozone production (e.g. Lin et al., 1988).
8) lines 242-243: You may add a reference for the selection of the 100 ppbv criterion for stratospheric ozone. For example, see Prather et al., 2011. Other model intercomparison studies generally utilized a chemical tropopause defined at the 150 ppbv (Young et al., 2013).
9) lines 251-253: The attribution of high NOx above 12 km to lightning NOx rather than NOx rich stratospheric air is rather speculative, unless if there are some indications from the model results or references for that. Mind also the simultaneous relatively smooth increase of both NO and O3 (as you also mention in page 10) which may point influence of stratospheric air.
10) line 264: At around 6 km it seems that there is an ozone layer of possible stratospheric origin. You may check this with relevant model diagnostics (e.g. specific humidity, potential vorticity or O3S if it is available from the simulation).
11) lines 280-281: This does not necessarily mean that you totally exclude the influence of mixing with air of stratospheric origin.
12) line 308: “ …is shown..” should be deleted.
13) line 368: Although the effect of humidity can be implied from factor α of Eq.4 maybe it is also interesting adding in the supplementary material the observed and simulated specific humidity values.
14) line 379: Should rather be : “ ... is from a factor of 2-3 (below 3 km altitude) to a factor of 10 (above 12 km altitude) stronger ... “
15) Figure 7 is interesting showing the NO dependence of NORP as well as the ozone compensation point (the NO level at which NORP is roughly zero). One possibly limitation is the fact that the aggregated bins correspond to different atmospheric layers with different atmospheric characteristics which can possibly induce the spiky signal in the figure.
16) line 441: You may also take into consideration the ozone compensation point which was derived in previous experimental studies in the free troposphere and which agrees well with these values (see e.g. Zanis et al., JGR, 2000).
- AC2: 'Reply on RC1', Ivan Tadic, 17 Mar 2021
- RC2: 'Comment on acp-2021-52', Anonymous Referee #2, 23 Mar 2021
Ivan Tadic et al.
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Central role of nitric oxide in ozone production in the upper tropical troposphere over the Atlantic Ocean and West Africa Ivan Tadic and Horst Fischer https://doi.org/10.5281/zenodo.4442616
Ivan Tadic et al.
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