Distinct sub-period trends in tropospheric ozone column over the East Asian outflow region during 1990-2019

Abstract Tropospheric ozone, an important greenhouse gas and pollutant, has increased over East Asia in recent decades. However, how this increase evolves temporally remains unclear. Here, we construct a global tropospheric ozone column (TrOC) dataset based on the Trajectory-mapped Ozonesonde dataset for the Stratosphere and Troposphere (TOST). This dataset reveals distinct TrOC sub-period trends over 1990-2019 in the East Asian outflow region: a slow increase (0.07 DU/year, 1990–2002), a rapid increase (1.26 DU/year, 2002–2008), and a non-significant decrease (2008–2019). While lower-tropospheric ozone continues to increase, declining ozone in higher layers drives the TrOC transition after 2008. Ensemble modeling, trajectory analysis, and tagged stratospheric ozone simulations attribute these TrOC changes to increasing chemical production and shifting stratospheric intrusion (SI) from increasing to decreasing, underscoring joint chemical and dynamical roles in shaping regional TrOC, particularly SI variability. Beyond this study, the observationally-constrained and spatially-explicit TOST TrOC would enable broader applications.