Causes of growing middle-to-upper tropospheric ozone over the northwest Pacific region
<p>Long-term ozone (O<span class="inline-formula"><sub>3</sub></span>) changes in the middle-to-upper troposphere are critical to climate radiative forcing and tropospheric O<span class="inline-formula"><sub>3</sub></span> pol...
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| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2025-01-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/25/943/2025/acp-25-943-2025.pdf |
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| Summary: | <p>Long-term ozone (O<span class="inline-formula"><sub>3</sub></span>) changes in the middle-to-upper troposphere are critical to climate radiative forcing and tropospheric O<span class="inline-formula"><sub>3</sub></span> pollution. Yet, these changes remain poorly quantified through observations in East Asia. Concerns also persist regarding the data quality of the ozonesondes available at the World Ozone and Ultraviolet Radiation Data Centre (WOUDC) for this region. This study aims to address these gaps by analyzing O<span class="inline-formula"><sub>3</sub></span> soundings at four sites along the northwestern Pacific coastal region over the past 3 decades and by assessing their consistency with an atmospheric chemistry–climate model simulation. Utilizing the European Centre for Medium-Range Weather Forecasts (ECMWF) Hamburg (ECHAM)/Modular Earth Submodel System (MESSy) Atmospheric Chemistry (EMAC) nudged simulations, it is demonstrated that trends between model and ozonesonde measurements are overall consistent, thereby gaining confidence in the model's ability to simulate O<span class="inline-formula"><sub>3</sub></span> trends and confirming the utility of potentially imperfect observational data. A notable increase in O<span class="inline-formula"><sub>3</sub></span> mixing ratio around 0.29–0.82 ppb a<span class="inline-formula"><sup>−1</sup></span> extending from the middle troposphere to the upper troposphere is observed in both observations and model simulations between 1990 and 2020, primarily during spring and summer. The timing of these O<span class="inline-formula"><sub>3</sub></span> tongues is delayed when moving from south to north along the measurement sites, transitioning from late spring to summer. Investigation into the drivers of these trends using tagged model tracers reveals that O<span class="inline-formula"><sub>3</sub></span> of stratospheric origin (O<span class="inline-formula"><sub>3</sub></span>S) dominates the absolute O<span class="inline-formula"><sub>3</sub></span> mixing ratios over the middle-to-upper troposphere in the subtropics, contributing to the observed O<span class="inline-formula"><sub>3</sub></span> increases by up to 96 % (40 %) during winter (summer), whereas O<span class="inline-formula"><sub>3</sub></span> of tropospheric origin (O<span class="inline-formula"><sub>3</sub></span>T) governs the absolute value throughout the tropical troposphere and contributes generally much more than 60 % to the positive O<span class="inline-formula"><sub>3</sub></span> changes, especially during summer and autumn. During winter and spring, a decrease in O<span class="inline-formula"><sub>3</sub></span>S is partly counterbalanced by an increase in O<span class="inline-formula"><sub>3</sub></span>T in the tropical troposphere. This study highlights that the enhanced downward transport of stratospheric O<span class="inline-formula"><sub>3</sub></span> into the troposphere in the subtropics and a surge of tropospheric O<span class="inline-formula"><sub>3</sub></span> in the tropics are the two key factors driving the enhancement of O<span class="inline-formula"><sub>3</sub></span> in the middle-to-upper troposphere along the northwest Pacific region.</p> |
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| ISSN: | 1680-7316 1680-7324 |