Very short-lived halogens amplify recent and future ozone depletion trends in the tropical lower stratosphere.

Recent observational evidences show ongoing net ozone depletion in the tropical lower stratosphere (LS) since the late 20^th century, in contrast to the overall stratospheric ozone recovery following controls in the Montreal Protocol to limit the production of long-lived ozone depleting substances. Such behavior is currently thought to be driven by dynamical transport accelerated by global warming. In contrast, the role of chemistry, i.e., the enhanced ozone depletion due to emissions of halogenated ozone-depleting very short-lived substances (VSLS) has been considered to be unimportant. Here we employ a chemistry-climate model with a comprehensive chemical scheme to demonstrate that VSLS chemistry accounts for around a quarter of the observed tropical LS negative ozone trend in 1998-2018. We attribute such an effect to chemical reactions with VSLS from natural and anthropogenic emissions in concert. Future projections show the persistence of the currently unaccounted for contribution of VSLS to ozone loss throughout the 21^st century in the tropical LS, the only region of the global stratosphere not projecting an ozone recovery by 2100. Our results show evidence for the need of mitigation strategies for regulating anthropogenic VSLS emissions to preserve the present and future ozone layer in low latitudes.