Convective injection into stratospheric intrusions alters tropopause chemical structure

Tropopause chemical structure (TCS) is influenced by the stratosphere-troposphere exchange (STE) and plays a role in Earth’s climate. Yet, this role is still not fully resolved in East Asia where active STE and high anthropogenic emissions coexist. Using airborne measurements of trace gases including O₃, CO and H₂O, we reveal the variations in TCS during two consecutive cut-off lows (COL), an important trigger of STE. We demonstrate the important roles of two-way STE and long-range transport processes in delivering natural and anthropogenic signatures in the TCS. The former COL case shows a normal pattern of TCS, consisting of stratospheric and tropospheric air and mixture of them. The latter, as a novel type of STE, exhibits an anomalous and complex structure, due to the deep convective injection into stratospheric intrusions, and advection of remote marine air. The distinct mixture of stratospheric air and anthropogenic pollution alters the TCS, with a horizontal and vertical scale estimated to be 200 km and 1 km, respectively. Moreover, air of maritime origins is also identified there, which is convectively transported and strongly dehydrated during the long-range transport. Such a complex TCS can produce unique chemical environments modulating cloud physics and atmospheric radiation. From a climatological perspective, events of these anomalous airmasses are nonnegligible in terms of their frequency and chemical impact revealed by multi-year observations. These new insights advance our understanding of the mixing of natural and anthropogenic species that shapes the TCS in East Asia, and have implications for climate change.