Causes of growing middle-to-upper tropospheric ozone over the northwest Pacific region
Year: 2025
Type: article
Abstract: Long-term ozone (O 3 ) changes in the middle-to-upper troposphere are critical to climate radiative forcing and tropospheric O 3 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 3 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 3 trends and confirming the utility of potentially imperfect observational data. A notable increase in O 3 mixing ratio around 0.29–0.82 ppb a −1 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 3 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 3 of stratospheric origin (O 3 S) dominates the absolute O 3 mixing ratios over the middle-to-upper troposphere in the subtropics, contributing to the observed O 3 increases by up to 96 % (40 %) during winter (summer), whereas O 3 of tropospheric origin (O 3 T) governs the absolute value throughout the tropical troposphere and contributes generally much more than 60 % to the positive O 3 changes, especially during summer and autumn. During winter and spring, a decrease in O 3 S is partly counterbalanced by an increase in O 3 T in the tropical troposphere. This study highlights that the enhanced downward transport of stratospheric O 3 into the troposphere in the subtropics and a surge of tropospheric O 3 in the tropics are the two key factors driving the enhancement of O 3 in the middle-to-upper troposphere along the northwest Pacific region.
Institutions: China Meteorological Administration, Forschungszentrum Jülich, Nanjing University of Information Science and Technology, National Oceanic and Atmospheric Administration, George Mason University, NOAA National Centers for Environmental Prediction, University of Reading, Deutsches Zentrum für Luft- und Raumfahrt e. V. (DLR)
Language: English
Subfield: Atmospheric Science
Field: Earth and Planetary Sciences
Domain: Physical Sciences
SDG: Climate action
Open Access status: gold
Estimated APC paid: $1,725
OpenAlex ID: W4406852960