the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Measurement report: Airborne measurements of NOx fluxes over Los Angeles during the RECAP-CA 2021 campaign
Clara M. Nussbaumer
Bryan K. Place
Qindan Zhu
Eva Y. Pfannerstill
Paul Wooldridge
Benjamin C. Schulze
Caleb Arata
Ryan Ward
Anthony Bucholtz
John H. Seinfeld
Allen H. Goldstein
Abstract. Nitrogen oxides (NOx ≡ NO + NO2) are involved in most atmospheric photochemistry, including the formation of tropospheric ozone (O3). While various methods exist to accurately measure NOx concentrations, it is still a challenge to quantify the source and flux of NOx emissions. We present airborne measurements of NOx and winds used to infer the emission of NOx across Los Angeles. The measurements were obtained during the research aircraft campaign RECAP-CA (Re-Evaluating the Chemistry of Air Pollutants in CAlifornia) in June 2021. Geographic allocations of the fluxes are compared to the NOx emission inventory from the California Air Resources Board (CARB). We find that the NOx fluxes have a pronounced weekend effect and are highest in the Eastern part of the San Bernardino valley. The comparison of the RECAP-CA and the modeled CARB NOx fluxes suggest the modeled emissions are too high near the coast and in downtown Los Angeles and too low further inland in the Eastern part of the San Bernardino valley.
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Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
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Supplement
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(3452 KB) - Metadata XML
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Supplement
(3542 KB) - BibTeX
- EndNote
- Final revised paper
Journal article(s) based on this preprint
Clara M. Nussbaumer et al.
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2023-601', Anonymous Referee #1, 30 May 2023
Clara M. Nussbaumer et al. presented the NOx fluxes from airborne measurements in Los Angeles during the aircraft campaign RECAP-CA. They showed both NOx concentrations and fluxes were higher in the weekdays and lower in the weekend. They also showed the difference between their calculated NOx fluxed and NOx emissions from the CARB inventory. The observations are valuable and very useful to the emission community. The paper is generally well rewritten. However, I still have some minor concerns before it can be published.Â
line 94: please add what is NOy, what species are included in the NOy ?
line 160-162: it was mentioned that the values of the NOx flux are dominated by the atmospheric variability. Can you explain a little more about it?
line 174 you are using the boundary layer height, where did you get the boundary layer height? Is it measured or modeled boundary layer height? What is the uncertainty of the boundary layer height?
Line 177 ‘the fit’ is the the linear fit of Fz and z/zi. Please mention it here.
Line 187. Please make it more clear what is the sensitivity study. Can you also provide a figure of the vertical divergence versus the dimensionless which excluding data points within the upper 20 % of the boundary layer? I get very confused by looking at Figure s4 and Figure s5. It would be nice if you also use different colors to indicate the density of the points.
Line 195-199: the footprint calculation is dependent on many variables and using the KL04 model. What are the meteo input for the model? Do you use measured data or data from meteo models?
Figure 4. What do the black lines indicate in figure 4? Are they the flight paths? Please mention it in the caption.
Line 300, what are ‘area emissions’?
Line 310-313, I don’t understand this part. The airport emissions were not captured by the measurements. How about comparing your NOx fluxes with the CARB emissions excluding aircraft emissions?
Line 325-330: In Figure 6 and Figure s10, NOx fluxes are quite different. Which one shows better results? Is it necessary to include the correction of vertical divergence in the flux calculation? Why are the emissions enhanced over Downtown Los Angeles and the inland highways in San Bernardino, but lower in the coastal region and Santa Ana? Please Add more discussion about the influence of vertical divergence.
Line 332 change ‘in-situ’ to ‘airborne’
Section 4: The conclusion section is only a short summary of the results. Please also indicate the implication of the study. What can we learn from the difference between the estimated NOx fluxes and the CARB inventory? What is your conclusion after investigating the influence of vertical divergence. Â Also discuss the limitation of the study and recommendations for future study.Â
Citation: https://doi.org/10.5194/egusphere-2023-601-RC1 - AC1: 'Reply on RC1', Clara M. Nussbaumer, 10 Aug 2023
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RC2: 'Comment on egusphere-2023-601', Glenn Wolfe, 02 Jun 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-601/egusphere-2023-601-RC2-supplement.pdf
- AC2: 'Reply on RC2', Clara M. Nussbaumer, 10 Aug 2023
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2023-601', Anonymous Referee #1, 30 May 2023
Clara M. Nussbaumer et al. presented the NOx fluxes from airborne measurements in Los Angeles during the aircraft campaign RECAP-CA. They showed both NOx concentrations and fluxes were higher in the weekdays and lower in the weekend. They also showed the difference between their calculated NOx fluxed and NOx emissions from the CARB inventory. The observations are valuable and very useful to the emission community. The paper is generally well rewritten. However, I still have some minor concerns before it can be published.Â
line 94: please add what is NOy, what species are included in the NOy ?
line 160-162: it was mentioned that the values of the NOx flux are dominated by the atmospheric variability. Can you explain a little more about it?
line 174 you are using the boundary layer height, where did you get the boundary layer height? Is it measured or modeled boundary layer height? What is the uncertainty of the boundary layer height?
Line 177 ‘the fit’ is the the linear fit of Fz and z/zi. Please mention it here.
Line 187. Please make it more clear what is the sensitivity study. Can you also provide a figure of the vertical divergence versus the dimensionless which excluding data points within the upper 20 % of the boundary layer? I get very confused by looking at Figure s4 and Figure s5. It would be nice if you also use different colors to indicate the density of the points.
Line 195-199: the footprint calculation is dependent on many variables and using the KL04 model. What are the meteo input for the model? Do you use measured data or data from meteo models?
Figure 4. What do the black lines indicate in figure 4? Are they the flight paths? Please mention it in the caption.
Line 300, what are ‘area emissions’?
Line 310-313, I don’t understand this part. The airport emissions were not captured by the measurements. How about comparing your NOx fluxes with the CARB emissions excluding aircraft emissions?
Line 325-330: In Figure 6 and Figure s10, NOx fluxes are quite different. Which one shows better results? Is it necessary to include the correction of vertical divergence in the flux calculation? Why are the emissions enhanced over Downtown Los Angeles and the inland highways in San Bernardino, but lower in the coastal region and Santa Ana? Please Add more discussion about the influence of vertical divergence.
Line 332 change ‘in-situ’ to ‘airborne’
Section 4: The conclusion section is only a short summary of the results. Please also indicate the implication of the study. What can we learn from the difference between the estimated NOx fluxes and the CARB inventory? What is your conclusion after investigating the influence of vertical divergence. Â Also discuss the limitation of the study and recommendations for future study.Â
Citation: https://doi.org/10.5194/egusphere-2023-601-RC1 - AC1: 'Reply on RC1', Clara M. Nussbaumer, 10 Aug 2023
-
RC2: 'Comment on egusphere-2023-601', Glenn Wolfe, 02 Jun 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-601/egusphere-2023-601-RC2-supplement.pdf
- AC2: 'Reply on RC2', Clara M. Nussbaumer, 10 Aug 2023
Peer review completion
Journal article(s) based on this preprint
Clara M. Nussbaumer et al.
Data sets
Supporting data for: Measurement report: Airborne measurements of NOx fluxes over Los Angeles during the RECAP-CA 2021 campaign Clara M. Nussbaumer, Bryan K. Place, Qindan Zhu, Eva Y. Pfannerstill, Paul Wooldridge, Benjamin C. Schulze, Caleb Arata, Ryan Ward, Anthony Bucholtz, John H. Seinfeld, Allen H. Goldstein, and Ronald C. Cohen https://doi.org/10.5281/zenodo.7786409
Clara M. Nussbaumer et al.
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(3452 KB) - Metadata XML
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Supplement
(3542 KB) - BibTeX
- EndNote
- Final revised paper