What the study found
The study found that global atmospheric chlorine inventories decreased from 2004 to 2024 across five latitude bands and altitudes from the surface to 61 km. It also found that source gases dominated chlorine profiles in the troposphere and lower stratosphere, while total chlorine at higher altitudes was dominated by source gases, reaching up to 99% by 61 km.
Why the authors say this matters
The authors conclude that these findings demonstrate the significant impact of the Montreal Protocol, an international agreement to phase out ozone-depleting substances, in reducing emissions of substances that are both ozone-depleting and greenhouse gases.
What the researchers tested
The researchers calculated atmospheric chlorine inventories over 21 years, from 2004 to 2024, using Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) version 5.3 retrievals of volume mixing ratios for 13 chlorine-containing species. They examined five latitude bands and altitudes from the surface to 61 km, and supplemented ACE-FTS data where needed with the TOMCAT 3-D chemical transport model, the Aura Microwave Limb Sounder, and ground-based measurements from NOAA and AGAGE.
What worked and what didn't
Total chlorine profiles were dominated by source gas contributions in the troposphere and lower stratosphere. At lower altitudes, chlorofluorocarbons, chlorocarbons, and increasingly in recent years chlorine-containing very short-lived substances were the main contributors; at higher altitudes, total chlorine became the dominant contributor, reaching up to 99% by 61 km. The global mean time series decreased by 2004-2024, with values approaching ppb in 2024, and the authors note that Cl-VSLS and HCFC-22 partially slowed the reduction achieved by the phase-out of CFC production and consumption.
What to keep in mind
The abstract does not describe detailed uncertainty estimates, and it does not provide full numerical values for the decrease in the text provided. It also summarizes results for the latitude bands and altitude range studied, so the findings are limited to those regions and the 2004-2024 period.
Key points
- Global atmospheric chlorine inventories decreased between 2004 and 2024.
- The analysis covered five latitude bands and altitudes from the surface to 61 km.
- Source gases dominated chlorine in the troposphere and lower stratosphere.
- At higher altitudes, total chlorine became the dominant contributor, reaching up to 99% by 61 km.
- Cl-VSLS and HCFC-22 partly slowed the decline in atmospheric chlorine.
Disclosure
- Research title:
- Global atmospheric chlorine declined from 2004 to 2024
- Authors:
- Neil Raymond, P. F. Bernath, C. Boone, M. P. Chipperfield
- Institutions:
- National Centre for Earth Observation, Old Dominion University, University of Leeds, University of Waterloo, University of Waterloo, University of Waterloo
- Publication date:
- 2026-03-09
- DOI:
- 10.1029/2025jd045176
- OpenAlex record:
- View
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