Emissions of ozone depleting substances used as feedstocks: scenarios
A recent paper by S. Reimann et al. “Continuing industrial emissions are delaying the recovery of the stratospheric ozone layer” [1] reports a scenario where the emission rates of ozone depleting substances used as feedstock continues as business as usual (BAU) until 2100, without any improvement in emission rates which occur during the production and use of feedstocks. This is compared to low emission rate (LOW) and zero emission rate (ZERO) scenarios. All the scenarios initially use BAU trends (growth or decrease depending on the feedstock) with feedstock use out to 2100 based on the authors considered likely trends. The authors then use the scenarios (BAU, LOW and ZERO) to estimate the effect on the recovery of the ozone layer and conclude that the elevated emission scenario (BAU) could delay the recovery of the mid-latitude stratospheric ozone layer by 7 (6 – 11) years from 2066 to 2073. The ZERO and LOW emission rate scenarios result in ozone layer recovery in 2065 and 2066 respectively.
The authors conclude that without additional measures, these elevated emissions (BAU) could delay the recovery of the mid-latitude stratospheric ozone layer and furthermore, limiting ODS feedstock emissions would also reduce their effect on direct radiative forcing and on climate change.
The BAU emission rate used by the authors is 3.6% [2], estimated by using bottom-up data, which is a combination of emissions from production (2.5%), distribution (0.5%), and the conversion of the ODS feedstocks into the final product (0.6%). This emission fraction of 3.6% is used as the default for the business-as-usual (BAU) scenario for ODS feedstocks (except CCl4) over the period 2024–2100. For CCl4, the slightly higher emission rate of 4.3% is applied. The LOW emission rate is 0.5% of production from 2024 onward, a 1994 estimate of feedstock-related emissions from existing well-designed and managed facilities [3]. The ZERO scenario is identical to the LOW scenario but assumes zero feedstock-related emissions from 2024 onward.
Explanatory Notes
Although the paper discusses scenarios for future feedstock use and emission rates, it is worth noting that according to TEAP 2026 Progress Report Vol.1 [4], reported ODS feedstock production, and use, as ODP tonnes, was at a maximum in 1993, reached a minimum in 1998 and in 2022, the quantity peaked at less than that reported in 1993. The large increase in ODS as metric tonnes since 1993 is due to the increased use of ODS feedstocks with lower ODPs, such as HCFC-22.
For the EU, according to the Ozone Depleting Substances 2025 report, in 2024 the emission rate from feedstock uses was 0.03% of the reported make-up. The 2024 average emission rate was slightly lower than the emission rate in 2023 (0.04%) and also marginally lower than the average emission rate obtained from earlier years (2016 to 2023) [5].
The EU share of global reported feedstock production and use for all controlled substances (ODS and HFCs) under the Montreal Protocol was < 5% in 2024. Lower emission rates in the EU would have only a minimal effect on overall global emission rates.
Emission rates. The paper discusses the selection of emission rates, commenting that emission rates (except of CCl4) were estimated to be 2–4%, based on the ratio of global emissions, derived from atmospheric measurements, against production reported to UNEP Ozone regulation. “For 1,1,1-trichloroethane, relative emissions are assessed at 2%, related to the 2019 ratio of global emissions against reported global production, 1,1,1-trichloroethane is an excellent tracer for generally estimating feedstock losses, because emissions from banks can be neglected, as it was historically used only as a solvent. For all other feedstock chemicals (except CCl4), emissions of 2–4% relative to their production were estimated, which covers the range between 2% and the Tier 1 default emissions factor of 4% for fluorochemical production (IPCC, 2019)” [6]. A recent paper by Wang et al. (2025) concluded that their results suggest the ocean has shifted from a net sink to a net source of 1,1,1-trichloroethane around 2005, outgassing 500 tonnes/year in the 2010s (up to 30% of inferred 1,1,1-trichloroethane emissions from atmospheric monitoring) [7]. It might be concluded from this paper that the emission rate of 2% in 2019 from feedstock use of 1,1,1-thichloroethane may be overstated. The BAU emission rate used by the authors is 3.6%, which is the most likely emission rate for modern-day, regulated manufacturing from production, supply chain, and use of feedstock (by weight of production). This is the mean of the most likely emission range (1.5% to 6.1%) which is meant to have general applicability across all substances and conditions for modern and well-maintained facilities [8].
EU Ozone Regulation 2024/590 requirements for feedstock use. In addition to Article 21. 1 “The intentional release of ozone-depleting substances into the atmosphere, including when contained in products and equipment, shall be prohibited where the release is not technically necessary for the intended uses permitted under this Regulation” there are specific reporting requirements for feedstock use. Annex VI.6. Each undertaking using ozone-depleting substances as feedstock or process agents shall communicate the following data, separately for each substance:
(a) any quantities used as feedstock or process agents;
(b) any stocks held at the beginning and the end of the reporting period;
(c) the types of feedstock uses and processes and any emissions, including those linked to transport and storage, including the transfer from one container to another.
References
[1] Reimann, S., Western, L.M., Lickley, M.J. et al. Continuing industrial emissions are delaying the recovery of the stratospheric ozone layer. Nat Commun 17, 3190 (2026). https://www.nature.com/articles/s41467-026-70533-w
[2] TEAP. Report of the Technology and Economic Assessment Panel, Volume 1: Progress Report. (2024). Available at Technology and Economic Assessment Panel (TEAP) | Ozone Secretariat
[3] TEAP. Report of the Technology and Economic Assessment Panel, Chapter 9. (1994).
[4] 2026 TEAP Progress Report – Volume 1 available on the ozone secretariat website as a pre-session document for the 48th meeting of the Open-ended Working Group of the Parties TEAP-May2026-Progress-Report-vol1.pdf
[5] European Environment Agency Ozone-depleting substances - 2025 | Climate change mitigation: reducing emissions | European Environment Agency (EEA)
[6] Daniel, J. S. et al. Scenarios and Information for Policymakers. World Meteorological Organization, Ozone Research and Monitoring –GAW Report No. 278, Scientific Assessment of Ozone Depletion 2022, Chapter 7 (2022). Available at Scientific Assessment Panel (SAP) | Ozone Secretariat
[7] Wang, P., Solomon, S., Scott, J. R., Yvon‐Lewis, S. A., Wennberg, P. O., Weiss, R. F., Rigby, M., and An, M. Ocean Outgassing of Methyl Chloroform as an Underestimated Source of Emission, Geophysical Research Letters 10.1029/2025GL118618 (2025) https://doi.org/10.1029/2025GL118618
[8] Medical and chemical Technical Options Committee, 2022 Assessment Report available at Technology and Economic Assessment Panel (TEAP) | Ozone Secretariat