Three‐Dimensional Distributions and Seasonality of Interannual Trends in the Stratospheric Contribution to Tropospheric Ozone Over China: A 37‐Year Modeling Study
Abstract
Stratospheric ozone (O3S) is a key natural source of tropospheric ozone, yet its vertical structure, seasonality, and interannual changes remain poorly characterized over China and surrounding regions. Leveraging 37 years of CESM2 simulations, which are rigorously evaluated against multi‐model ensembles and observational data sets for both horizontal and vertical ozone distributions, this study characterizes the three‐dimensional spatial distribution of O3S and quantifies its contribution to tropospheric ozone, with focused analysis on seasonal cycles and interannual trends across China and adjacent Asia. Results reveal that O3S concentrations decrease equatorward, peaking in the upper troposphere during winter and contributing over 70% to ozone concentration in northeastern China. O3S concentrations decline downward, and near‐surface O3S contribution reaches a maximum (∼60%) in winter and a minimum (∼10%) in summer over eastern China, demonstrating strong seasonality. Over the 37‐year period, O3S concentration exhibits significant positive trends in the mid‐to‐upper troposphere. However, its relative contribution to tropospheric ozone shows insignificant increasing trends in the free troposphere and even declines in the mid‐latitude subregions. Near the surface, interannual trends in O3S contribution display a pronounced seasonal pattern over eastern China with +0.6%·yr−1 in winter and −0.1%·yr−1 in summer. The vertical distribution of O3S concentration and contribution to the troposphere varies markedly across regions and seasons, reflecting the combined effects of multiscale atmospheric processes, including stratosphere–troposphere exchange, large‐scale transport, and terrain forcing. These findings provide a quantitative baseline for disentangling the distinct role of stratospheric intrusions in shaping tropospheric ozone changes over China.