Chlorinated very short-lived substances offset the long-term reduction of inorganic stratospheric chlorine

Dubé, Kimberlee and Tegtmeier, Susann and Bourassa, Adam and Laube, Johannes C. and Engel, Andreas and Saunders, Laura N. and Walker, Kaley A. and Hossaini, Ryan and Bednarz, Ewa M. (2025) Chlorinated very short-lived substances offset the long-term reduction of inorganic stratospheric chlorine. Communications Earth & Environment, 6 (1): 487. ISSN 2662-4435

Abstract

Over the past few decades, a reduction in chlorinated long-lived ozone-depleting substance emissions due to the regulations imposed by the Montreal Protocol has led to a global decrease in stratospheric chlorine. At the same time, emissions of chlorinated Very Short-Lived Substances, which are unregulated, have increased. Here we show that observed changes of inorganic stratospheric chlorine are inconsistent with changes in the tropospheric abundances of long-lived ozone-depleting substances. Satellite observations of stratospheric chlorine species from the Atmospheric Chemistry Experiment—Fourier Transform Spectrometer during 2004–2020 reveal that the observed decrease in inorganic stratospheric chlorine is 25%–30% smaller than expected based on trends of long-lived ozone-depleting substances alone. At mid-latitudes in the lower stratosphere, this can be explained by the chlorinated Very Short-Lived Substances increase, which offsets the long-term reduction of stratospheric chlorine by up to 30%.