Increase in global emissions of HFC-23 despite near-total expected reductions

Effective realization of abatement measures can reduce HFC-23 emissions

HFC-23 is a potent greenhouse gas, predominantly emitted as an undesired by-product during the synthesis and processing of HCFC-22 (ref. 1). Previously, the Clean Development Mechanism and national efforts called for the implementation of abatement technology for reducing HFC-23 emissions2,3. Nevertheless, between 2015 and 2019, a divergence was found between the global emissions derived from atmospheric observations and those expected from reported abatement1,2. Primarily, this points to insufficient implementation of abatement strategies2,4, calling for independent verification of the emissions at the individual chemical facility level. Here we use regional atmospheric observations and a new, deliberately released tracer to quantify the HFC-23 emissions from an HCFC-22 and fluoropolymer production facility, which is equipped with waste gas destruction technology. We find that our inferred HFC-23/HCFC-22 emission factor of 0.19% (0.13-0.24%) broadly fits within the emission factor considered practicable for abatement projects5,6. Extrapolation to global HCFC-22 production underscores that the operation of appropriate destruction technology has the potential to reduce global HFC-23 emissions by at least 84% (69-100%) (14 (12-16) Gg yr-1). This reduction is equivalent to 17% CO2 emissions from aviation in 2019 (ref. 7). We also demonstrate co-destruction of PFC-318, another by-product and greenhouse gas. Our findings show the importance of the 2016 Kigali Amendment to the Montreal Protocol, which obligates parties to destroy HFC-23 emissions from facilities manufacturing hydrochlorofluorocarbons and hydrofluorocarbons "to the extent practicable" from 2020 onwards8.

On the Chemical Pathways Influencing the Effective Global Warming Potential of Commercial Hydrofluoroolefin Gases

The enforcement of a global hydrofluorocarbon (HFC) refrigerant phase down led to the introduction of hydrofluoroolefins (HFOs) as a low Global Warming Potential (GWP) substitute, given their low atmospheric lifetime. However, to this date it is not fully clear the long-term atmospheric fate of HFOs primary degradation products: trifluoro acetaldehyde (TFE), trifluoro acetyl fluoride (TFF), and trifluoroacetic acid (TFA). It particularly concerns the possibility of forming HFC-23, a potent global warming agent. Although the atmospheric reaction networks of TFE, TFF, and TFA have a fair level of complexity, the relevant atmospheric chemical pathways are well characterized in the literature, enabling a comprehensive hazard assessment of HFC-23 formation as a secondary HFO breakdown product in diverse scenarios. A lower bound of the HFOs effective GWP in a baseline scenario is found above regulatory thresholds. While further research is crucial to refine climate risk assessments, the existing evidence suggests a non-negligible climate hazard associated with HFOs.

Low-k nano-dielectrics facilitate electric-field induced phase transition in high-k ferroelectric polymers for sustainable electrocaloric refrigeration

Ferroelectric polymer-based electrocaloric effect may lead to sustainable heat pumps and refrigeration owing to the large electrocaloric-induced entropy changes, flexible, lightweight and zero-global warming potential. Herein, low-k nanodiamonds are served as extrinsic dielectric fillers to fabricate polymeric nanocomposites for electrocaloric refrigeration. As low-k nanofillers are naturally polar-inactive, hence they have been widely applied for consolidate electrical stability in dielectrics. Interestingly, we observe that the nanodiamonds markedly enhances the electrocaloric effect in relaxor ferroelectrics. Compared with their high-k counterparts that have been extensively studied in the field of electrocaloric nanocomposites, the nanodiamonds introduces the highest volumetric electrocaloric enhancement (~23%/vol%). The resulting polymeric nanocomposite exhibits concurrently improved electrocaloric effect (160%), thermal conductivity (175%) and electrical stability (125%), which allow a fluid-solid coupling-based electrocaloric refrigerator to exhibit an improved coefficient of performance from 0.8 to 5.3 (660%) while maintaining high cooling power (over 240 W) at a temperature span of 10 K.

Trifluoroiodomethane as a Precursor to High Global Warming Potential Climate Pollutants: Could the Transformation of Climatically Benign CF3I into Potent Greenhouse Gases Significantly Increase Refrigerant-Related Greenhouse Gas Emissions?

The transition away from the production and consumption of high global warming potential (GWP) hydrofluorocarbons (HFCs) under the 2016 Kigali Amendment to the Montreal Protocol on Substances that Deplete the Ozone Layer (Montreal Protocol) has prompted air conditioning, refrigeration, and heat pump equipment manufacturers to seek alternative refrigerants with lower direct climate impacts. Additional factors affecting alternative refrigerant choice include safety (i.e., flammability and toxicity), environmental, and thermodynamic constraints. At the same time, manufacturers are incentivized to seek refrigerants with higher energy efficiency, which saves on electricity costs and reduces indirect greenhouse gas emissions from electricity generation. The life cycle climate performance (LCCP) metric is commonly used to assess the combined direct and indirect climate impacts of refrigerant-use equipment. Here, we consider an additional impact on climate performance: the degradation of refrigerant in equipment, i.e., the direct climate impacts of high-GWP byproducts that can form as the result of adding trifluoroiodomethane (CF3I) to refrigerant blends to reduce flammability. Such a production of high-GWP gases could change the acceptability of CF3I-containing refrigerants. Further, it highlights the need to understand refrigerant degradation within equipment in calculations of the environmental acceptability of new cooling technology.

In Situ Observations of Halogenated Gases at the Shangdianzi Background Station and Emission Estimates for Northern China

Halogenated gases include ozone-depleting substances and greenhouse gases, such as chlorofluorocarbons, halons, hydrochlorofluorocarbons, hydrofluorocarbons, and perfluorinated gases. In situ atmospheric observations of major halogenated gases were conducted at the Shangdianzi (SDZ) background station, China, from October 2020 to September 2021 using ODS5-pro, a newly developed measurement system. The measurement time series of 36 halogenated gases showed occasional pollution events, where background conditions represented 25% (CH₂Cl₂) to 81% (CF₃Cl, CFC-13) of the measurements. The annual mean background mole fractions of most species at SDZ were consistent with those obtained at the Mace Head station in Ireland. The background conditions were distinguished from pollution events, and the enhanced mole fractions were used to estimate the emissions of four categories of fluorinated gases (F-gases) from northern China using a tracer ratio method. The CO₂-equivalent (CO₂-equiv) emission of F-gases from northern China reached 181 ± 18 Tg year^-1 during 2020-2021. Among the four categories of F-gases estimated, SF₆ accounted for the highest proportion of CO₂-equiv emissions (24%), followed by HFC-23 (22%), HFC-125 (17%), HFC-134a (13%), NF₃ (10%), CF₄ (5.9%), HFC-143a (3.9%), HFC-32 (3.4%), and HFC-152a (0.2%).

Historical trend of ozone-depleting substances and hydrofluorocarbon concentrations during 2004-2020 derived from satellite observations and estimates for global emissions

Global concentrations (or mole fractions) and emissions of ozone-depleting substances (ODSs) and their hydrofluorocarbon (HFCs) substitutes that are controlled by the Montreal Protocol and its Amendments and adjustments (MP) are of great interest to both the scientific community and public. Previous studies on global concentrations and emissions have mostly relied on ground-based observations. Here, we assess the global concentrations and emissions of eight MP controlled substances and methyl chloride from ACE-FTS (Atmospheric Chemistry Experiment high-resolution infrared Fourier transform spectrometer) satellite observations: CFC-11 (CFCl₃), CFC-12 (CF₂Cl₂), CCl₄, HCFC-22 (CHClF₂), HCFC-141b (C₂H₃Cl₂F), HCFC-142b (C₂H₃ClF₂), HFC-23 (CHF₃), HFC-134a (C₂H₂F₄), and CH₃Cl. Results show that the ACE-FTS satellite observations can be used to derive the concentrations and emissions of these ODSs, HFCs, and CH₃Cl, as they are consistent with those derived from the ground-based observations. Our findings imply that the changes in the concentrations and emissions of the ODSs and HFCs closely match the regulatory status of the MP, and satellite observations can be used to monitor the past and future progress of the MP.

Deep near-term mitigation of short-lived climate forcers in Oman: grand challenges and prospects

Over time, short-lived climate forcers (SLCFs) have gradually gained prominence as a rationale in the international global mitigation strategy to preserve temperature below 1.5 °C by the end of this century. Scientists cite the short-term gains in air quality and health co-benefits associated with reducing SLCFs as grounds for raising the pressure on governments to eliminate SLCFs rapidly and aggressively. There is little research on whether deep SLCF mitigation during the next decade is feasible in low- and middle-income nations, particularly the hydrocarbon-based economy. This study estimates current and future emissions of potent SLCFs as methane (CH₄) hydrofluorocarbons (HFCs) in Oman using the basic tier 1 approach of the Intergovernmental Panel on Climate Change (IPCC) greenhouse gases (GHG) inventory Guidelines of 2006. Current and future emission of black carbon (BC) was also quantified using specific emission factors. A total of 38,268 Gg of SLFCs were released into the atmosphere in Oman in 2015, accounting for 38.8% of the country's total GHG emissions, and is expected to rise significantly over the next decade to reach 67,777 Gg by 2030. The analysis reveals that the source of Oman's highly potent SLCF emissions is associated with key and critical economic sectors such as the oil and gas industry, heavy road transportation, residential air conditioning (RAC), and industrial refrigeration. These vital economic sectors impose a "Grand Challenge" on the immediate reduction of SLCFs in Oman and the Gulf Cooperation Council (GCC). Accomplishing a rapid, significant reduction in highly potent SLCFs from the three challenging sectors over a 5- to 10-year time period does not appear feasible or realistic in the context of international market mechanisms, socioeconomic factors, and mitigation targets. Achieving a significant reduction in SLCFs for a hydrocarbon-based economy requires a profound economic shift. Creating an effective long-term vision for a post-oil economy over the next two decades provides a sound foundation for implementing economic and societal transformation policies incorporating near-zero-emission measures for the potent SLCFs.

Opportunities to tackle short-lived climate pollutants and other greenhouse gases for China

To limit the global temperature increase to below 1.5 °C, it is critical to reduce not only carbon dioxide (CO₂), but also specific non-CO₂ greenhouse gases (GHGs) and precursors, including some short-lived climate pollutants (SLCPs). These include emissions of black carbon, methane (CH4), tropospheric ozone, and fluorinated gases such as hydrofluorocarbons (HFCs). As the largest CH4 emitter and second-largest HFCs emitter, China plays a critical role in global efforts to reduce SLCPs and has acknowledged the need to reduce non-CO₂ GHGs in its 2060 carbon neutrality goal. This study reviewed leading international experiences with SLCP reduction to identify global best practices to inform target development and policy actions in China and elsewhere. We used bottom-up modeling and scenario analysis to evaluate pathways of non-CO₂ emission mitigation in China to 2050, drawing on mitigation measures developed through updated 2030 and 2050 cost curves. We identified a cost-effective reduction potential of 35 % for methane, 30 % for fluorinated gases, and 40 % for nitrous oxides-another potent GHG-in 2030 relative to 2015 levels for China under a Deep Non-CO₂ Mitigation scenario. Annual total reduction potential of 1080 million metric tons of CO₂ equivalent is also possible by 2030. For long-term targets, progress made on reducing SLCPs could help China reach its carbon neutrality target by 2060. While some uncertainties regarding the long-term mitigation potential of SLCPs remain, our analyses suggest that the fast adoption of available cost-effective technologies could allow China to reduce its non-CO₂ GHGs by 56 % by 2050.

Repurposing of F-gases: challenges and opportunities in fluorine chemistry

Fluorinated gases (F-gases) are routinely employed as refrigerants, blowing agents, and electrical insulators. These volatile compounds are potent greenhouse gases and consequently their release to the environment creates a significant contribution to global warming. This review article seeks to summarise: (i) the current applications of F-gases, (ii) the environmental issues caused by F-gases, (iii) current methods of destruction of F-gases and (iv) recent work in the field towards the chemical repurposing of F-gases. There is a great opportunity to tackle the environmental and sustainability issues created by F-gases by developing reactions that repurpose these molecules.

Mid-infrared-scanning cavity ring-down CH2F2 detection using electronically tuned Cr:ZnSe laser

The development of mid-infrared (mid-IR) tunable lasers has been driving various laser spectroscopic technologies. Herein, we report wavelength-scanning cavity ring-down spectroscopy (WS-CRDS) in the mid-IR region using an electronically tuned Cr:ZnSe (ET-Cr:ZnSe) laser, which could achieve a nanosecond pulse operation, with broad wavelength tuning of 2-3 µm. This allowed WS-CRDS-induced trace detection of the refrigerant, CH₂F₂. A CH₂F₂ detection limit of 0.66 ppm (3σ), and the detection of trace H₂O in CH₂F₂ was realized using the broad wavelength-tuning range feature, demonstrating the effectiveness of the ET-Cr:ZnSe laser in WS-CRDS. We believe that our method would accelerate the development of various trace-gas detection technologies.

Rapid increase in dichloromethane emissions from China inferred through atmospheric observations

With the successful implementation of the Montreal Protocol on Substances that Deplete the Ozone Layer, the atmospheric abundance of ozone-depleting substances continues to decrease slowly and the Antarctic ozone hole is showing signs of recovery. However, growing emissions of unregulated short-lived anthropogenic chlorocarbons are offsetting some of these gains. Here, we report an increase in emissions from China of the industrially produced chlorocarbon, dichloromethane (CH2Cl2). The emissions grew from 231 (213-245) Gg yr-1 in 2011 to 628 (599-658) Gg yr-1 in 2019, with an average annual increase of 13 (12-15) %, primarily from eastern China. The overall increase in CH2Cl2 emissions from China has the same magnitude as the global emission rise of 354 (281-427) Gg yr-1 over the same period. If global CH2Cl2 emissions remain at 2019 levels, they could lead to a delay in Antarctic ozone recovery of around 5 years compared to a scenario with no CH2Cl2 emissions.

Narrowing feedstock exemptions under the Montreal Protocol has multiple environmental benefits

The Montreal Protocol on Substances that Deplete the Ozone Layer (Montreal Protocol) can be further strengthened to control ozone-depleting substances and hydrofluorocarbons used as feedstocks to provide additional protection of the stratospheric ozone layer and the climate system while also mitigating plastics pollution. The feedstock exemptions were premised on the assumption that feedstocks presented an insignificant threat to the environment; experience has shown that this is incorrect. Through its adjustment procedures, the Montreal Protocol can narrow the scope of feedstock exemptions to reduce inadvertent and unauthorized emissions while continuing to exempt production of feedstocks for time-limited, essential uses. This upstream approach can be an effective and efficient complement to other efforts to reduce plastic pollution. Existing mechanisms in the Montreal Protocol such as the Assessment Panels and national implementation strategies can guide the choice of environmentally superior substitutes for feedstock-derived plastics. This paper provides a framework for policy makers, industries, and civil society to consider how stronger actions under the Montreal Protocol can complement other chemical and environmental treaties.

A horizon scan of global biological conservation issues for 2022

We present the results of our 13th annual horizon scan of issues likely to impact on biodiversity conservation. Issues are either novel within the biological conservation sector or could cause a substantial step-change in impact, either globally or regionally. Our global panel of 26 scientists and practitioners identified 15 issues that we believe to represent the highest priorities for tracking and action. Many of the issues we identified, including the impact of satellite megaconstellations and the use of long-distance wireless energy transfer, have both elements of threats and emerging opportunities. A recent state-sponsored application to commence deep-sea mining represents a significant step-change in impact. We hope that this horizon scan will increase research and policy attention on the highlighted issues.

Emerging reporting and verification needs under the Paris Agreement: How can the research community effectively contribute?

Greenhouse gas (GHG) emission inventories represent the link between national and international political actions on climate change, and climate and environmental sciences. Inventory agencies need to include, in national GHG inventories, emission and removal estimates based on scientific data following specific reporting guidance under the United Nation Framework Convention on Climate Change (UNFCCC) and the Paris Agreement, using the methodologies defined in the Intergovernmental Panel on Climate Change (IPCC) Guidelines. Often however, research communities and inventory agencies have approached the problem of climate change from different angles and by using terminologies, metrics, rules and approaches that do not always match. This is particularly true dealing with "Land Use, Land-Use Change and Forestry" (LULUCF), the most challenging among the inventory sectors to deal with, mainly because of high level of complexity of its carbon dynamics and the difficulties in disaggregating the fluxes between those caused by natural and anthropogenic processes. In this paper, we facilitate the understanding by research communities of the current (UNFCCC) and future (under the Paris Agreement) reporting requirements, and we identify the main issues and topics that should be considered when targeting improvement of the GHG inventory. In relation to these topics, we describe where and how the research community can contribute to producing useful inputs, data, methods and solutions for inventory agencies and policy makers, on the basis of available literature. However, a greater effort by both communities is desirable for closer cooperation and collaboration, for data sharing and the understanding of respective and common aims.

Waste Management Strategies to Mitigate the Effects of Fluorinated Greenhouse Gases on Climate Change

Fluorinated greenhouse gases (F-gases) are used for various applications, such as in refrigeration and air conditioning, as substitutes of the ozone-depleting substances. Their utilization has increased drastically over the last few decades, with serious consequences for global warming. The Kigali Amendment to the Montreal Protocol and several national and international legislations, such as the 2014 EU F-gas Regulation, aim to control the utilization and emissions of these gases. In the EU, the phase-down of hydrofluorocarbons (HFCs) is underway, with successive reductions in quotas up to 2050. Under this scenario, efficient strategies for managing the produced and already existing F-gases are of vital importance to guarantee that their effect on the environment is mitigated. Up to now, most of the F-gases recovered from end-of-life equipment or when retrofitting systems are either released into the atmosphere or destroyed. However, in order to put forward a cost-efficient adaptation to the F-gas phase-down, increasing separation and recycling efforts must be made. This critical review aims at providing a revision of the current F-gas management problems and strategies and providing an overview on the innovative strategies that can be applied to contribute to build a sustainable market under circular economy principles.

Unexpected nascent atmospheric emissions of three ozone-depleting hydrochlorofluorocarbons

Global and regional atmospheric measurements and modeling can play key roles in discovering and quantifying unexpected nascent emissions of environmentally important substances. We focus here on three hydrochlorofluorocarbons (HCFCs) that are restricted by the Montreal Protocol because of their roles in stratospheric ozone depletion. Based on measurements of archived air samples and on in situ measurements at stations of the Advanced Global Atmospheric Gases Experiment (AGAGE) network, we report global abundances, trends, and regional enhancements for HCFC-132b ([Formula: see text]), which is newly discovered in the atmosphere, and updated results for HCFC-133a ([Formula: see text]) and HCFC-31 ([Formula: see text]ClF). No purposeful end-use is known for any of these compounds. We find that HCFC-132b appeared in the atmosphere 20 y ago and that its global emissions increased to 1.1 Gg⋅y-1 by 2019. Regional top-down emission estimates for East Asia, based on high-frequency measurements for 2016-2019, account for ∼95% of the global HCFC-132b emissions and for ∼80% of the global HCFC-133a emissions of 2.3 Gg⋅y-1 during this period. Global emissions of HCFC-31 for the same period are 0.71 Gg⋅y-1 Small European emissions of HCFC-132b and HCFC-133a, found in southeastern France, ceased in early 2017 when a fluorocarbon production facility in that area closed. Although unreported emissive end-uses cannot be ruled out, all three compounds are most likely emitted as intermediate by-products in chemical production pathways. Identification of harmful emissions to the atmosphere at an early stage can guide the effective development of global and regional environmental policy.

Signaling Network Centered on mTORC1 Dominates Mammalian Intestinal Stem Cell Ageing

The intestine integrates the function of digestion, absorption, and barrier, which is easily damaged by the external factors upon ageing. The intestinal stem cells (ISCs) exist at the intestinal crypt base and play an indispensable role in intestinal homeostasis and regeneration. The intestine ageing contributes to malabsorption and other associated illnesses, which were considered to be related to ISCs. Here, we summarize the current research progress of mammalian ISCs ageing and pay more attention to the central regulatory role of the mTORC1 signaling pathway in regulating mammalian ISCs ageing, and its related AMPK, FOXO, Wnt signaling pathways. Furthermore, we also discuss the interventions aimed at mTORC1 and its associated signaling pathways, which may provide potential strategies for rejuvenating aged ISCs and the therapy of age-related intestinal diseases. Graphical abstract Many signaling pathways are altered in the ageing ISCs, thereby inducing the decrease of ISC self-renewal, differentiation, and regeneration, an increasing of oxidative stress may contribute to damage to the ISCs. Interventions such as calorie restriction, fasting and so on can effectively alleviate these adverse effects.