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  Central role of nitric oxide in ozone production in the upper tropical troposphere over the Atlantic Ocean and West Africa

Tadic, I., Nussbaumer, C., Bohn, B., Harder, H., Marno, D., Martinez, M., et al. (2021). Central role of nitric oxide in ozone production in the upper tropical troposphere over the Atlantic Ocean and West Africa. Atmospheric Chemistry and Physics Discussions, 21. doi:10.5194/acp-2021-52.

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Tadic, Ivan1, Author              
Nussbaumer, Clara1, Author              
Bohn, Birger, Author
Harder, Hartwig1, Author              
Marno, Daniel1, Author              
Martinez, Monica1, Author              
Obersteiner, Florian, Author
Parchatka, Uwe1, Author              
Pozzer, Andrea1, Author              
Rohloff, Roland1, Author              
Zöger, Martin, Author
Lelieveld, Jos1, Author              
Fischer, Horst1, Author              
Affiliations:
1Atmospheric Chemistry, Max Planck Institute for Chemistry, Max Planck Society, ou_1826285              

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 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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Language(s): eng - English
 Dates: 2021-01-25
 Publication Status: Published online
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Type: -
 Identifiers: DOI: 10.5194/acp-2021-52
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Title: Atmospheric Chemistry and Physics Discussions
  Abbreviation : Atmos. Chem. Phys. Discuss.
Source Genre: Journal
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Publ. Info: Katlenburg-Lindau, Germany : European Geophysical Society, Copernicus Publ.
Pages: 24 Volume / Issue: 21 Sequence Number: - Start / End Page: - Identifier: ISSN: 1680-7367
CoNE: https://pure.mpg.de/cone/journals/resource/111076360006006