Characterization of reactive oxidized nitrogen in the global upper troposphere using recent and historic commercial and research aircraft campaigns and GEOS-Chem
<p>Reactive oxidized nitrogen (NO<span class="inline-formula"><sub><i>y</i></sub></span>) in the upper troposphere (UT) influences global climate, air quality, and tropospheric oxidants, but this understanding is limited by knowledge of the relativ...
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| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2025-07-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/25/7925/2025/acp-25-7925-2025.pdf |
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| Summary: | <p>Reactive oxidized nitrogen (NO<span class="inline-formula"><sub><i>y</i></sub></span>) in the upper troposphere (UT) influences global climate, air quality, and tropospheric oxidants, but this understanding is limited by knowledge of the relative contributions of individual NO<span class="inline-formula"><sub><i>y</i></sub></span> components in this undersampled layer. Here, we use sporadic NASA DC-8 aircraft campaign observations, after screening for plumes and stratospheric influence, to characterize UT NO<span class="inline-formula"><sub><i>y</i></sub></span> composition and to evaluate current knowledge of UT NO<span class="inline-formula"><sub><i>y</i></sub></span> as simulated by the GEOS-Chem model. The use of DC-8 data follows confirmation that these intermittent data reproduce NO<span class="inline-formula"><sub><i>y</i></sub></span> seasonality from routine commercial aircraft observations (2003–2019), supporting the use of DC-8 data to characterize UT NO<span class="inline-formula"><sub><i>y</i></sub></span>. We find that peroxyacetyl nitrate (PAN) dominates UT NO<span class="inline-formula"><sub><i>y</i></sub></span> (30 %–64 % of NO<span class="inline-formula"><sub><i>y</i></sub></span>), followed by nitrogen oxides (NO<span class="inline-formula"><sub><i>x</i></sub>≡</span> NO <span class="inline-formula">+</span> NO<span class="inline-formula"><sub>2</sub></span>) (6 %–18 %), peroxynitric acid (HNO<span class="inline-formula"><sub>4</sub></span>) (6 %–13 %), and nitric acid (HNO<span class="inline-formula"><sub>3</sub></span>) (7 %–11 %). Methyl peroxy nitrate (MPN) makes an outsized contribution to NO<span class="inline-formula"><sub><i>y</i></sub></span> (14 %–24 %) over the Southeast US relative to the other regions sampled (2 %–7 %). GEOS-Chem, sampled along DC-8 flights, exhibits much weaker seasonality than the DC-8, underestimating summer and spring NO<span class="inline-formula"><sub><i>y</i></sub></span> and overestimating winter and autumn NO<span class="inline-formula"><sub><i>y</i></sub></span>. The model consistently overestimates peroxypropionyl nitrate (PPN) by <span class="inline-formula">∼</span> 10–16 pptv or 10 %–90 % and underestimates NO<span class="inline-formula"><sub>2</sub></span> by 6–36 pptv or 31 %–65 %, as the model is missing PPN photolysis. A model underestimate in MPN of at least <span class="inline-formula">∼</span> 50 pptv (13-fold) over the Southeast US results from uncertainties in processes that sustain MPN production as air ages. Our findings highlight that a greater understanding of UT NO<span class="inline-formula"><sub><i>y</i></sub></span> is critically needed to determine its role in the nitrogen cycle, air pollution, climate, and the abundance of oxidants.</p> |
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| ISSN: | 1680-7316 1680-7324 |