Ray F. Weiss

The Kigali Amendment to the Montreal Protocol requires parties to destroy, to the extent practicable, HFC-23 generated as a byproduct during the production of controlled hydrochlorofluorocarbons and hydrofluorocarbons. Global total HFC-23 emissions estimated from reported abatement and known sources (bottom-up) agreed with those inferred from atmospheric observations (top-down) before 2015, but have been substantially lower since then. Here, we show that during 2011–2013, bottom-up estimates of global total HFC-23 emissions were right for the wrong reasons: bottom-up estimates for the non-Article 5 (mainly developed) country group were lower than top-down estimates (1.7 ± 0.2 vs 3.1 ± 0.5 Gg yr–1 on average), while those for the Article 5 (mainly developing) country group were higher (11.8 ± 0.4 vs 9.7 ± 1.0 Gg yr–1), resulting in a cancellation at the global scale. We further show that during 2015–2023, while the underestimation of global bottom-up emissions was dominated by the Article 5 country group, the non-Article 5 country group also contributed in 2023 [bottom-up (byproduct emissions reported to UNEP plus other known sources) vs top-down: 0.5 ± 0.2 vs 1.3 ± 0.6 Gg yr–1]. Our results underscore improvement of emission accounting and mitigation for both country groups under the Kigali Amendment.

The perfluorocarbons CF₄ and C₂F₆ are among the most potent greenhouse gases with lifetimes of fifty and ten thousand years, respectively. They are both primarily emitted during aluminum smelting and electronics manufacturing. We perform the first regionally resolved global inversion of CF₄ and C₂F₆, providing atmospheric measurement-based top-down emission estimates for 2006–2023 using the FLEXPART transport model and the FLEXINVERT+ framework. Introducing a global-total constraint to align the inversion results with the relatively accurate global total emissions from the AGAGE 12-box model stabilizes the emissions in poorly monitored regions. Compared to the global bottom-up inventory EDGAR, the inversion increases global CF₄ and C₂F₆ emissions by factors of 2.6 ± 0.3 and 3.1 ± 0.7, respectively, for 2018–2023. China dominates global emissions, contributing 56 % (CF₄) and 58 % (C₂F₆) in 2018–2023. The contribution of South and Southeast Asia to global emissions rose from about 6 % and 10 % in 2006–2011 to 22 % and 18 % by 2018–2023, respectively, though large uncertainties remain due to a lack of measurements in the region itself. European emissions declined until 2010, then stabilized and contribute 2 %–3 % to global emissions by 2018–2023. U.S. CF₄ emissions remain constant and C₂F₆ emissions decreased steadily (reaching 3 %–4 % by 2018–2023), with a temporary drop in 2009 likely linked to the financial crisis. On the global scale, our results suggest a contribution of 81 % by the aluminum industry to total CF₄ emissions and 48 % by the electronics industry to global C₂F₆ emissions.

The onset of the COVID‐19 pandemic in North America and the lockdowns that followed in March 2020 brought forth a rapid change to societal functions disrupting many aspects of normal life, including the greenhouse gas emissions associated with them. In this work, we examine the capabilities of tower networks established in six North American cities in quantifying the change in these emissions. Influence functions, which relate tower‐based observational sites to their upwind source regions, were created for sites in Los Angeles, the D.C./Baltimore urban corridor, Indianapolis, Salt Lake City, Boston, and Toronto for the months of February–April of 2017–2020, and model CO ₂ enhancements were generated by multiplying the influence functions by regional inventories. Scaling factors are assigned to the city emissions to minimize the difference between observed and modeled afternoon CO ₂ enhancements in 15 days intervals. Scaling factors from the 2020 period are then compared directly to those from the 2017 to 2019 timeframe to calculate a relative change in the emissions during the COVID‐lockdown timeframe. Results across all six cities show a consistent message; by the end of March 2020, CO ₂ emissions decreased by an average of 34% relative to the same 2017–2019 timeframe. This decrease matches values observed from bottom‐up inventories during the same period. A similar technique is performed for methane across four cities with more variable trends across cities. The results of this paper demonstrate the ability to utilize simple approaches to detect and quantify temporal changes in emissions using a tower network.

For the first time, we present long-term, ongoing atmospheric measurements of 1,2-dichloroethane (DCE, CH ₂ ClCH ₂ Cl) from the Advanced Global Atmospheric Gases Experiment (AGAGE) and National Oceanic and Atmospheric Administration (NOAA) global monitoring networks. DCE is an industrially produced, very short-lived chlorinated substance (Cl-VSLS) that has the potential to contribute chlorine to the stratosphere and cause ozone depletion. Compared to other Cl-VSLS, DCE is produced in higher volumes for its primary use as a feedstock in polyvinyl chloride (PVC) manufacture. This production has sustained annual mean mole fractions at the Earth's surface of between 5 and 10 ppt during 2017–2023, making it the third most abundant Cl-VSLS after dichloromethane and chloroform. In this study we estimate mean global emissions for 2017–2023 of 453 ± 185 Gg yr ⁻¹ using the AGAGE observations, and 525 ± 209 Gg yr ⁻¹ using the NOAA observations. We also use AGAGE measurements to estimate regional emissions for northwest Europe (2.06 [1.31, 2.65] Gg yr ⁻¹ ) and California (0.23 [0, 0.37] Gg yr ⁻¹ ), two domains with sufficient observational coverage to enable this approach. Our global emissions estimates are consistent (within uncertainties) with the only previously published estimate by Hossaini et al. (2024), whereas our regional emissions estimates are at least an order of magnitude smaller than those in that study. This suggests global total emissions may be well constrained, but their spatial distribution remains uncertain.

Hydrofluoroolefins (HFOs) are important synthetic compounds replacing other halocarbons in phase-down from usage (e.g., as refrigerants, propellants, foam blowing). Little is known about their atmospheric abundance, distribution and trends, nor about their emissons. Here, we report atmospheric observations of the widely used HFO-1234yf (2,3,3,3-tetrafluoroprop-1-ene), and HFO-1234ze(E) (E-1,3,3,3-tetrafluoroprop-1-ene), and the hydrochlorofluoroolefin (HCFO) HCFO-1233zd(E) (E-1-chloro-3,3,3-trifluoroprop-1-ene) observed as part of the Advanced Global Atmospheric Gases Experiment (AGAGE) network. Over the observational period 2011–2025, pollution events have grown in magnitude and frequency at sites which are influenced by regional emissions, while remote stations show first appearances of these substances. By 2024/2025 winter peak mole fractions in background northern hemisphere air have reached ∼ 0.25 ppt (picomol mol−1, parts-per-trillion in dry air) for HFO-1234yf and HFO-1234ze(E) and ∼ 0.45 ppt for HCFO-1233zd(E). Using European observations and the inverse modeling frameworks InTEM, ELRIS, and RHIME we determine emission trends and regional distributions. For Northwest Europe, emissions of HFO-1234yf increased steadily and rapidly from <0.1 Gg yr−1 in 2014 to 1.50 [1.23–1.74, range of 16–84 percentile] Gg yr−1 by 2023, presumably due to its introduction in mobile air conditioning and stationary refrigeration. HFO-1234ze(E) emissions were low during 2014–2017, followed by a rapid increase in 2018/2019, potentially due its introduction as an aerosol propellant, after which they increased more slowly to 0.96 [0.82–1.13] Gg yr−1 by 2023. HCFO-1233zd(E) emissions are derived from 2017 onward, showing a steady increase from 0.15 [0.07–0.23] to 1.04 [0.93–1.15] Gg yr−1 in 2023.

For the first time, we present long-term, ongoing atmospheric measurements of 1,2-dichloroethane (DCE, CH₂ClCH₂Cl) from the Advanced Global Atmospheric Gases Experiment (AGAGE) and National Oceanic and Atmospheric Administration (NOAA) global monitoring networks. DCE is an industrially produced, very short-lived chlorinated substance (Cl-VSLS) that has the potential to contribute chlorine to the stratosphere and cause ozone depletion. Compared to other Cl-VSLS, DCE is produced in higher volumes for its primary use as a feedstock in polyvinyl chloride (PVC) manufacture. This production has sustained annual mean mole fractions at the Earth’s surface of between 5 and 10 ppt during 2017–2023, making it the third most abundant Cl-VSLS. In this study we estimate mean global emissions for 2017–2023 of 453 [268, 638] Gg yr⁻¹ using the AGAGE observations, and 525 [316, 734] Gg yr⁻¹ using the NOAA observations. We also use AGAGE measurements to estimate regional emissions for northwest Europe (2.06 [1.31, 2.65] Gg yr⁻¹) and California (0.23 [0, 0.37] Gg yr⁻¹), two domains with sufficient observational coverage to enable this approach. Our global emissions estimates are consistent (within uncertainties) with the only previously published estimate by Hossaini et al. (2024), whereas our regional emission estimates are at least an order of magnitude smaller than those in that study. This suggests global total emissions may be well constrained, but their spatial distribution remains uncertain. Improved measurement coverage in key source regions of DCE could address that uncertainty and better constrain the contribution of DCE to ozone-depleting chlorine in the stratosphere.

For the first time, we present long-term, ongoing atmospheric measurements of 1,2-dichloroethane (DCE, CH₂ClCH₂Cl) from the Advanced Global Atmospheric Gases Experiment (AGAGE) and National Oceanic and Atmospheric Administration (NOAA) global monitoring networks. DCE is an industrially produced, very short-lived chlorinated substance (Cl-VSLS) that has the potential to contribute chlorine to the stratosphere and cause ozone depletion. Compared to other Cl-VSLS, DCE is produced in higher volumes for its primary use as a feedstock in polyvinyl chloride (PVC) manufacture. This production has sustained annual mean mole fractions at the Earth’s surface of between 5 and 10 ppt during 2017–2023, making it the third most abundant Cl-VSLS. In this study we estimate mean global emissions for 2017–2023 of 453 [268, 638] Gg yr⁻¹ using the AGAGE observations, and 525 [316, 734] Gg yr⁻¹ using the NOAA observations. We also use AGAGE measurements to estimate regional emissions for northwest Europe (2.06 [1.31, 2.65] Gg yr⁻¹) and California (0.23 [0, 0.37] Gg yr⁻¹), two domains with sufficient observational coverage to enable this approach. Our global emissions estimates are consistent (within uncertainties) with the only previously published estimate by Hossaini et al. (2024), whereas our regional emission estimates are at least an order of magnitude smaller than those in that study. This suggests global total emissions may be well constrained, but their spatial distribution remains uncertain. Improved measurement coverage in key source regions of DCE could address that uncertainty and better constrain the contribution of DCE to ozone-depleting chlorine in the stratosphere.

For the first time, we present long-term, ongoing atmospheric measurements of 1,2-dichloroethane (DCE, CH₂ClCH₂Cl) from the Advanced Global Atmospheric Gases Experiment (AGAGE) and National Oceanic and Atmospheric Administration (NOAA) global monitoring networks. DCE is an industrially produced, very short-lived chlorinated substance (Cl-VSLS) that has the potential to contribute chlorine to the stratosphere and cause ozone depletion. Compared to other Cl-VSLS, DCE is produced in higher volumes for its primary use as a feedstock in polyvinyl chloride (PVC) manufacture. This production has sustained annual mean mole fractions at the Earth’s surface of between 5 and 10 ppt during 2017–2023, making it the third most abundant Cl-VSLS. In this study we estimate mean global emissions for 2017–2023 of 453 [268, 638] Gg yr⁻¹ using the AGAGE observations, and 525 [316, 734] Gg yr⁻¹ using the NOAA observations. We also use AGAGE measurements to estimate regional emissions for northwest Europe (2.06 [1.31, 2.65] Gg yr⁻¹) and California (0.23 [0, 0.37] Gg yr⁻¹), two domains with sufficient observational coverage to enable this approach. Our global emissions estimates are consistent (within uncertainties) with the only previously published estimate by Hossaini et al. (2024), whereas our regional emission estimates are at least an order of magnitude smaller than those in that study. This suggests global total emissions may be well constrained, but their spatial distribution remains uncertain. Improved measurement coverage in key source regions of DCE could address that uncertainty and better constrain the contribution of DCE to ozone-depleting chlorine in the stratosphere.

For the first time, we present long-term, ongoing atmospheric measurements of 1,2-dichloroethane (DCE, CH₂ClCH₂Cl) from the Advanced Global Atmospheric Gases Experiment (AGAGE) and National Oceanic and Atmospheric Administration (NOAA) global monitoring networks. DCE is an industrially produced, very short-lived chlorinated substance (Cl-VSLS) that has the potential to contribute chlorine to the stratosphere and cause ozone depletion. Compared to other Cl-VSLS, DCE is produced in higher volumes for its primary use as a feedstock in polyvinyl chloride (PVC) manufacture. This production has sustained annual mean mole fractions at the Earth’s surface of between 5 and 10 ppt during 2017–2023, making it the third most abundant Cl-VSLS. In this study we estimate mean global emissions for 2017–2023 of 453 [268, 638] Gg yr⁻¹ using the AGAGE observations, and 525 [316, 734] Gg yr⁻¹ using the NOAA observations. We also use AGAGE measurements to estimate regional emissions for northwest Europe (2.06 [1.31, 2.65] Gg yr⁻¹) and California (0.23 [0, 0.37] Gg yr⁻¹), two domains with sufficient observational coverage to enable this approach. Our global emissions estimates are consistent (within uncertainties) with the only previously published estimate by Hossaini et al. (2024), whereas our regional emission estimates are at least an order of magnitude smaller than those in that study. This suggests global total emissions may be well constrained, but their spatial distribution remains uncertain. Improved measurement coverage in key source regions of DCE could address that uncertainty and better constrain the contribution of DCE to ozone-depleting chlorine in the stratosphere.

The perfluorocarbons CF₄ and C₂F₆ are among the most potent greenhouse gases with lifetimes of fifty and ten thousand years, respectively. They are both primarily emitted during aluminum smelting and electronics manufacturing. We perform the first regionally resolved global inversion of CF₄ and C₂F₆, providing atmospheric measurement-based top-down emission estimates for 2006–2023 using the FLEXPART transport model and the FLEXINVERT+ framework. Introducing a global-total constraint to align the inversion results with the relatively accurate global total emissions from the AGAGE 12-box model stabilizes the emissions in poorly monitored regions. Compared to the global bottom-up inventory EDGAR, the inversion increases global CF₄ and C₂F₆ emissions by factors of 2.6 ± 0.3 and 3.1 ± 0.7, respectively, for 2018–2023. China dominates global emissions, contributing 56 % (CF₄) and 58 % (C₂F₆) in 2018–2023. The contribution of South and Southeast Asia to global emissions rose from about 6 % and 10 % in 2006–2011 to 22 % and 18 % by 2018–2023, respectively, though large uncertainties remain due to a lack of measurements in the region itself. European emissions declined until 2010, then stabilized and contribute 2 %–3 % to global emissions by 2018–2023. U.S. CF₄ emissions remain constant and C₂F₆ emissions decreased steadily (reaching 3 %–4 % by 2018–2023), with a temporary drop in 2009 likely linked to the financial crisis. On the global scale, our results suggest a contribution of 81 % by the aluminum industry to total CF₄ emissions and 48 % by the electronics industry to global C₂F₆ emissions.