Asian Summer Monsoon Anticyclone—The Primary Entryway for Chlorinated Very-Short-Lived Substances to the Stratosphere

Rapid growing emissions of dichloromethane (CH₂Cl₂), a chlorinated very-short-lived substance (Cl-VSLS) and an ozone depleting substance (ODS), has raised concerns as this increase offset a part of the stratospheric chlorine (Cl) reduction due to decreasing long-lived ODSs. We have combined simulations of the two most abundant Cl-VSLSs, CH₂Cl₂ and chloroform (CHCl₃) using the NASA GEOS Chemistry Climate Model (GEOSCCM) with Asian Summer Monsoon Chemical and CLimate Impact Project aircraft observations to examine transport of Cl-VSLSs to the stratosphere and to assess their contribution to total stratospheric Cl. With ongoing large emissions (total ∼1,500 Gg yr⁻¹), Cl-VSLSs add about 100 ppt Cl to the stratosphere between 2020 and 2022. The Asian Summer Monsoon plays a primary role in the troposphere-to-stratosphere transport of Cl-VSLSs and delivers double the amount to the stratosphere, about 200 ppt Cl in August 2022. The overall Cl-VSLSs impact on stratospheric chlorine (∼3.3%) and ozone (∼1 DU) remain small.