What the study found
The study found that global atmospheric chlorine inventories declined over 2004–2024, with the total amount approaching parts per billion in 2024. The authors report that the decline was partly slowed by chlorine-containing very short-lived substances and HCFC-22, while the Montreal Protocol is described as having a significant impact on reducing emissions of ozone-depleting substances and greenhouse gases.
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. They also note that the measured chlorine-containing substances include both ozone-depleting and greenhouse gases.
What the researchers tested
The researchers calculated atmospheric chlorine inventories over 21 years, from 2004 to 2024, across five latitude bands and altitudes from the surface to 61 km. They used Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) version 5.3 measurements of 13 chlorine-containing species, and supplemented the data where needed with the TOMCAT chemical transport model, Aura Microwave Limb Sounder observations, and ground-based measurements from NOAA and AGAGE.
What worked and what didn't
The inventories showed that source gases dominated total chlorine in the troposphere and lower stratosphere. At lower altitudes, chlorofluorocarbons, chlorocarbons, and increasingly chlorine-containing very short-lived substances were important contributors, while at higher altitudes chlorine monoxide became the dominant contributor, reaching up to 99% of total chlorine by 61 km. The global mean total chlorine time series decreased by an amount given in the abstract as ppt/year, with values approaching ppb in 2024.
What to keep in mind
The abstract does not provide the numerical values for some reported quantities, so those are not fully recoverable here. It also does not describe detailed uncertainties, and the summary available here is limited to the abstract and title.
Key points
- Global atmospheric chlorine inventories were estimated for 2004–2024 across five latitude bands and altitudes up to 61 km.
- Total chlorine decreased over time, with the global mean time series approaching ppb in 2024.
- Source gases dominated chlorine in the troposphere and lower stratosphere, while chlorine monoxide dominated at higher altitudes.
- Cl-containing very short-lived substances and HCFC-22 partially slowed the reduction in atmospheric chlorine.
- The authors say the findings show the Montreal Protocol had a significant impact on reducing emissions.
Disclosure
- Research title:
- Global atmospheric chlorine inventories declined over 2004–2024
- 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
- OpenAlex record:
- View
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