25 Jan 2021

25 Jan 2021

Review status: this preprint is currently under review for the journal ACP.

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

Ivan Tadic1, Clara Nussbaumer1, Birger Bohn2, Hartwig Harder1, Daniel Marno1, Monica Martinez1, Florian Obersteiner3, Uwe Parchatka1, Andrea Pozzer1,4, Roland Rohloff1, Martin Zöger5, Jos Lelieveld1,6, and Horst Fischer1 Ivan Tadic et al.
  • 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.

Ivan Tadic et al.

Status: open (until 31 Mar 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on acp-2021-52, ozone measurement technique', Florian Obersteiner, 29 Jan 2021 reply
    • AC1: 'Reply on CC1', Ivan Tadic, 08 Feb 2021 reply

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

Ivan Tadic et al.


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Short summary
Although mechanisms of tropospheric ozone (O3) formation are well understood, studies reporting on ozone formation derived from field measurements are challenging and remain sparse in number. We use airborne measurements to quantify nitric oxide (NO) and O3 distributions in the upper troposphere over the Atlantic Ocean and West Africa and compare our measurements to model simulations. Our results show that NO and ozone formation are greatest over the tropical areas of West Africa.