Changes in Stratosphere-Troposphere Exchange of Air Mass and Ozone Concentration in CCMI Models From 1960 to 2099

This study investigates changes in stratosphere-troposphere exchange (STE) of air masses and ozone concentrations from 1960 to 2099 using multiple model simulations from Chemistry Climate Model Initiative (CCMI) under climate change scenario RCP6.0. We employ a lowermost stratosphere mass budget approach with dynamic isentropic surfaces fitted to the tropical tropopause as the upper boundary of lowermost stratosphere. The multi-model mean (MMM) trends of air mass STEs are all small over all regions, which are within 0.3 (0.1) % decade(-1) for 1960-2000 (2000-2099). The MMM trends of ozone STE for 1960-2000 are 0.3%, -2.7%, 3.4%, -0.9%, and -2.7% decade(-1) over the Northern hemisphere (NH) extratropics, Southern hemisphere (SH) extratropics, tropics, extratropics, and globe, respectively. The corresponding ozone STE trends for 2000-2099 are 3.0%, 4.3%, 0.8%, 3.5%, and 4.7% decade(-1). Changes in ozone STEs are dominated by ozone concentration changes, driven by climate-induced changes and ozone-depleting substance (ODS) changes. For 1960-2000, small changes in ozone STEs in the NH extratropics are due to a cancellation between effects of climate-induced changes and ODS increases, while the ODS effect dominates in the SH extratropics, leading to a large ozone STE magnitude decrease. Increased ozone transport from tropical troposphere to stratosphere for 1960-2000 is due to increased tropospheric ozone. A decreased global ozone STE magnitude for 1960-2000 was largely caused by ODS-induced ozone loss that is partly compensated by climate-induced ozone changes. For 2000-2099, about two-thirds of global ozone STE magnitude increases are caused by ozone increases in the extratropical lower stratosphere due to climate-induced changes. The remaining one-third is caused by ozone recovery due to the phaseout of ODS.Plain Language Summary Stratosphere-troposphere exchange (STE) of ozone is an important source of tropospheric ozone and can impact the tropospheric air quality. This study investigates changes in STE of ozone concentrations for 1960-2099 using multiple climate model simulations from the Chemistry Climate Model Initiative under the RCP6.0 scenario. It is shown that the trends in global ozone STEs are -2.7% decade(-1) for 1960-2000, and 4.7% decade (-1) for 2000-2099 in. In other words, global ozone STEs are decreased by 11% from 1960 to 2000, but increased by 47% from 2000 to 2099. We separate the contributions from climate change and ozone-depleting substance (ODS) effects to the ozone STE changes. A decreased global ozone STE magnitude for 1960-2000 was caused by ODS-induced ozone loss that is partly compensated by climate-induced ozone changes. For 2000-2099, about two-thirds of the global ozone STE magnitude increases are caused by ozone increases in the extratropical lower stratosphere due to climate changes. The remaining one-third is caused by ozone recovery due to the phaseout of ODS.

Automated summary

This study investigates changes in stratosphere-troposphere exchange (STE) of air masses and ozone concentrations from 1960 to 2099. The results show that global ozone STE decreased by 11% from 1960 to 2000, but increased by 47% from 2000 to 2099. The changes in ozone STE are mainly driven by ozone concentration changes, including climate-induced changes and ozone-depleting substance (ODS) changes.