Ozone Formation Sensitivity to Precursors and Lightning in the Tropical Troposphere Based on Airborne Observations.
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| Title: | Ozone Formation Sensitivity to Precursors and Lightning in the Tropical Troposphere Based on Airborne Observations. |
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| Authors: | Nussbaumer, Clara M.1 (AUTHOR) clara.nussbaumer@mpic.de, Kohl, Matthias1 (AUTHOR), Pozzer, Andrea1,2 (AUTHOR), Tadic, Ivan1 (AUTHOR), Rohloff, Roland1 (AUTHOR), Marno, Daniel1 (AUTHOR), Harder, Hartwig1 (AUTHOR), Ziereis, Helmut3 (AUTHOR), Zahn, Andreas4 (AUTHOR), Obersteiner, Florian4 (AUTHOR), Hofzumahaus, Andreas5 (AUTHOR), Fuchs, Hendrik5 (AUTHOR), Künstler, Christopher5 (AUTHOR), Brune, William H.6 (AUTHOR), Ryerson, Tom B.7 (AUTHOR), Peischl, Jeff8,9 (AUTHOR), Thompson, Chelsea R.8 (AUTHOR), Bourgeois, Ilann8,9,10 (AUTHOR), Lelieveld, Jos1,2 (AUTHOR), Fischer, Horst1 (AUTHOR) |
| Source: | Journal of Geophysical Research. Atmospheres. 7/28/2024, Vol. 129 Issue 14, p1-16. 16p. |
| Subject Terms: | *Trace gases, *Troposphere, *Air pollutants, *Tropospheric ozone, *Nitrogen oxides, Peroxy radicals, Atmospheric models, Tropospheric chemistry |
| Abstract: | Tropospheric ozone (O3) is an important greenhouse gas that is also hazardous to human health. The formation of O3 is sensitive to the levels of its precursors NOx (≡NO + NO2) and peroxy radicals, for example, generated by the oxidation of volatile organic compounds (VOCs). A better understanding of this sensitivity will show how changes in the levels of these trace gases could affect O3 levels today and in the future, and thus air quality and climate. In this study, we investigate O3 sensitivity in the tropical troposphere based on in situ observations of NO, HO2 and O3 from four research aircraft campaigns between 2015 and 2023. These are OMO (Oxidation Mechanism Observations), ATom (Atmospheric Tomography Mission), CAFE Africa (Chemistry of the Atmosphere Field Experiment in Africa) and CAFE Brazil, in combination with simulations using the EMAC atmospheric chemistry—climate model. We use the metric α(CH3O2) together with NO to investigate the O3 formation sensitivity. We show that O3 formation is generally NOx‐sensitive in the lower and middle tropical troposphere and is in a transition regime in the upper troposphere. By distinguishing observations impacted by lightning or not we show that NO from lightning is the most important driver of O3 sensitivity in the tropics. NOx‐sensitive chemistry predominates in regions without lightning impact, with α(CH3O2) ranging between 0.56 and 0.82 and observed average O3 levels between 35 and 55 ppbv. Areas affected by lightning exhibit strongly VOC‐sensitive O3 chemistry with α(CH3O2) of about 1 and average O3 levels between 55 and 80 ppbv. Plain Language Summary: Ozone (O3) in the troposphere is both an air pollutant and a greenhouse gas. It is formed from nitrogen oxides (NOx) and volatile organic compounds (VOCs). The formation can be sensitive to either of these precursors depending on their abundance. Considering the high relevance of O3 in regard to human health and global warming, it is important to understand this sensitivity of O3 formation, which allows to predict future changes in O3. Here, we investigate O3 formation sensitivity toward NOx and VOCs in the tropical troposphere based on aircraft measurements during four research campaigns between 2015 and 2023, and a global model. We include observations of NO, HO2 (hydroperoxyl radicals) and O3 over South America, the Middle East and the Pacific, Atlantic and Indian Ocean. We find that O3 formation is sensitive to NOx in the lower tropical troposphere. In the upper tropical troposphere, lightning events control O3 chemistry and promote strong VOC‐sensitive O3 formation. Key Points: α(CH3O2) correlated with NO is a powerful metric for indicating O3 sensitivity and is valid throughout the troposphereO3 chemistry in the remote tropical lower troposphere is found to be NOx‐sensitiveNO emissions from lightning drive O3 sensitivity in the tropical upper troposphere and induce highly VOC‐sensitive chemistry [ABSTRACT FROM AUTHOR] |
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| Database: | GreenFILE |
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