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 similar to 0.25 ppt (picomol mol(-1), parts-per-trillion in dry air) for HFO-1234yf and HFO-1234ze(E) and similar to 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.

Hydrofluorocarbons (HFCs) with high global warming potential are regulated under the Kigali Amendment to the Montreal Protocol. While China began freezing production and consumption of HFCs in 2024, there are discrepancies among previous activity-based bottom-up emissions estimates and lack of observation-based inverse modelling emissions estimates of China’s HFC emissions since 2017. Here we use atmospheric observations across China and inverse modelling to reveal distinct emissions trends of nine HFCs from 2011 to 2021 in China. Our top-down emissions estimates reveal an overestimation of HFC emissions post-2017 by an average of 117.2 Tg CO2-equivalent per year, by China’s national official bottom-up emissions inventories. Also, we find that while eastern China is the largest emitter of HFCs in China (37.4

Abstract Nitrous oxide (N2O) is a strong greenhouse gas that contributes significantly to global warming and causes depletion of ozone in the stratosphere. Recent observational records show an unprecedented acceleration in atmospheric N₂O growth, reaching 1.15 ppb yr− 1 in 2019–2023, a significant increase compared to 0.68 ppb yr− 1 in 2001–2005. This surge in growth rate is particularly pronounced over tropical regions, and has been measured most prominently at the southern-most island of Japan (Hateruma). In this study, we use N2O observations from globally distributed multi-institutional networks and the MIROC4-ACTM inversion framework to quantify N2O emissions and identify key regions that are driving the recent acceleration. Our results suggest that the major Asian countries, Brazil, Central and Northern Africa, and the Contiguous United States have increased emission sources in the recent 2.5 decades (1998–2023). Further, there has been an increase in land N2O emissions, at a rate of 106 GgN yr− 1 per year during 1998–2002 to 2019–2023 (1Gg = 109g). The inversion inferred trends are consistent with increased fertiliser use and manure production to support extensive agriculture, and terrestrial ecosystem model results. The emissions from oceanic regions did not show significant increases in N2O (rate: 7 ± 2 GgN yr− 1 per year) in our inverse model setup. Our results underscore the importance for improved climate mitigation strategies and emissions reduction policies by increasing nitrogen-fertiliser use efficiency in agricultural land.

Halon-2402 (1,2-dibromotetrafluoroethane, H-2402) is a potent ozone-depleting substance and greenhouse gas whose global production has been banned under the Montreal Protocol since 2010, while the use of recovered or recycled stocks remains permitted for essential uses. Although these controls led to nearly two decades of declining atmospheric abundances, recent observations indicate renewed emissions. Here, we present the first observation-based regional emission estimates of H-2402 in East Asia for 2008-2023, derived using high-frequency measurements at Gosan, South Korea, and a Bayesian inversion framework. While most AGAGE stations measure background mole fractions or intermittent low-level increases, Gosan exhibits increasingly frequent and intense pollution events, revealing growing regional emissions. We find that East Asia accounted for most global H-2402 emissions in recent years, with particularly sharp increases in Japan and the Vladivostok region of Russia. Since 2015, regional emissions from East Asia have effectively driven the global emission trend, reversing the long-term decline. These emissions are spatially linked to petrochemical infrastructure, ship-repair activity, and military decommissioning sites, suggesting releases from legacy halon banks rather than new production. Cumulative emissions from East Asia between 2008 and 2023 reached similar to 52 Gg CFC-11-equivalent emissions. These findings imply a tangible delay in ozone layer recovery and underscore the urgent need for strengthened monitoring, transparent reporting, and verifiable management of remaining H-2402 stocks under the Montreal Protocol.

Estimates of trace gas baseline mole fractions in high-frequency atmospheric measurement records are crucial for analysing long-term changes in atmospheric composition. Baseline mole fractions are those that would be observed far from emission sources (and hence are representative of background conditions). Previous methods for inferring baseline mole fractions have used statistical or meteorological approaches, or, if available, co-measured tracer species thought only to be emitted from non-baseline wind sectors. Combinations of these techniques have also been employed in some applications. Statistical methods typically fit a baseline to the observations themselves, while meteorological methods use atmospheric models of varying complexity to categorise air mass origins. In this paper, we present a novel machine learning method for estimating trace gas baseline mole fractions, which benefits from the physical basis of model-based filtering without the need for running an expensive simulator. Our approach offers the accessibility and computational cost-effectiveness of statistical models, without the associated smoothing or difficulty in identifying rapid baseline variations. By training on historical Lagrangian particle dispersion model outputs, our model learns to predict baseline mole fractions directly from meteorological fields. This advancement opens new avenues for low-latency trace gas time series data analysis, reconstruction of historical baseline trends, and improved utilisation of tracer measurement air mass classification methods.

Carbon tetrachloride (CCl4) is a long-lived ozone-depleting substance that has been controlled by the Montreal Protocol on Substances that Deplete the Ozone Layer. Despite the global phase-out of production and consumption for dispersive uses of CCl4 since 2010, its global emissions have still been substantial and persistent for more than a decade, potentially delaying the recovery of the ozone layer, with ~30-40% of the sources of global CCl4 emissions remaining largely unknown.In this study, we focus on CCl4 emissions in China, a major contributor to global halocarbon emissions. We determined top-down CCl4 emissions in China over 2011-2021, using long-term atmospheric observations from a Chinese network (including AGAGE measurements made at one station) and an inverse modelling approach. We identified substantial and persistent emissions of CCl4 in China over the time period despite its complete phase-out, without a statistically significant decreasing trend in the emissions during the period. These CCl4 emissions in China are comparable to global total annual hydrochlorofluorocarbons (HCFCs) emissions in terms of the CFC-11-eq emissions in 2020. We also compiled a bottom-up CCl4 emission inventory for China, incorporating emission sources that have been proposed to be able to close the majority of the global CCl4 emissions budget from recent studies. We identified substantial CCl4 emissions from allowed feedstock use, from feedstock use for the renewed production of CFC-11 over 2013-2018, and from by-product emissions in chlorine-related processes. After considering these major sources, substantial top-down CCl4 emissions sources still remained unaccounted-for in China, which could account for more than half of the reported global unaccounted-for emission budget in 2014 and 2019. However, the magnitude of the unaccounted-for CCl4 emissions may have decreased in China over 2011-2021.

Abstract. 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.

Hydrochlorofluorocarbons (HCFCs) are ozone-depleting substances whose production and consumption have been phased out under the Montreal Protocol in non-Article 5 (mainly developed) countries and are currently being phased out in the rest of the world. Here, we focus on two HCFCs, HCFC-123 and HCFC-124, whose emissions are not decreasing globally in line with their phase-out. We present the first measurement-derived estimates of global HCFC-123 emissions (1993–2023) and updated HCFC-124 emissions for 1978–2023. Around 5 Gg yr−1 of HCFC-123 and 3 Gg yr−1 of HCFC-124 were emitted in 2023. Both HCFC-123 and HCFC-124 are intermediates in the production of HFC-125, a non-ozone-depleting hydrofluorocarbon (HFC) that has replaced ozone-depleting substances in many applications. We show that it is possible that the observed global increase in HCFC-124 emissions could be entirely due to leakage from the production of HFC-125, provided that its leakage rate is around 1 % by mass of HFC-125 production. Global emissions of HCFC-123 have not decreased despite its phase-out for production under the Montreal Protocol, and its use in HFC-125 production may be a contributing factor to this. Emissions of HCFC-124 from western Europe, the USA and East Asia have either fallen or not increased since 2015 and together cannot explain the entire increase in the derived global emissions of HCFC-124. These findings add to the growing evidence that emissions of some ozone-depleting substances are increasing due to leakage and improper destruction during fluorochemical production.

Nitrous oxide (N₂O) is a strong greenhouse gas that contributes significantly to global warming and causes depletion of ozone in the stratosphere. Recent observational records show an unprecedented acceleration in atmospheric N₂O growth, reaching 1.15 ppb yr-1 in 2019–2023, a significant increase compared to 0.68 ppb yr-1 in 2001–2005. This surge in growth rate is particularly pronounced over tropical regions. In this study, we use N₂O observations from globally distributed multi-institutional networks and the MIROC4-ACTM inversion framework to quantify N₂O emissions and identify key regions that are driving the recent acceleration. Our results suggest that the major Asian countries, Brazil, Central and Northern Africa, and the Coterminous United States have increased emission sources in the recent 2.5 decades (1998-2023). Further, the increase in land N2O emissions, at a rate of 106 GgN yr-2 during 1998-2002 to 2019-2023 (1Gg=109g), has been clearly associated with the use of nitrogen fertilisers to support extensive agriculture, as inferred from a terrestrial ecosystem model, statistics of nitrogen fertiliser use and inversion results. The emissions from oceanic regions did not show significant increases in N2O emissions (rate: 7±2 GgN yr-2). Our results underscore the importance for improved climate mitigation strategies and emissions reduction policies by increasing nitrogen-fertiliser use efficiency (NUE) in agricultural land.

Lingering global emissions of carbon tetrachloride (CCl4) are slowing ozone layer recovery. Estimates of global CCl4 emissions based on observed atmospheric mole fractions and inverse modelling (top down) exceed the emissions derived from known sources (bottom up) by 30–40

Measurements from the Advanced Global Atmospheric Gases Experiment (AGAGE) combined with a global 12-box model of the atmosphere have long been used to estimate global emissions and surface mean mole fraction trends of atmospheric trace gases. Here, we present annually updated estimates of these global emissions and mole fraction trends for 42 compounds through 2023 measured by the AGAGE network, including chlorofluorocarbons, hydrochlorofluorocarbons, hydrofluorocarbons, perfluorocarbons, sulfur hexafluoride, nitrogen trifluoride, methane, nitrous oxide, and selected other compounds. The data sets are available at https://doi.org/10.5281/zenodo.15372480 (Western et al., 2025). We describe the methodology to derive global mole fraction and emissions trends, which includes the calculation of semihemispheric monthly mean mole fractions, the mechanics of the 12-box model and the inverse method that is used to estimate emissions from the observations and model. Finally, we present examples of the emissions and mole fraction data sets for the 42 compounds.

Nitrogen trifluoride (NF3) is a potent and long-lived greenhouse gas that is widely used in the manufacture of semiconductors, photovoltaic cells, and flat panel displays. Using atmospheric observations from eight monitoring stations from the Advanced Global Atmospheric Gases Experiment (AGAGE) and inverse modeling with a global 3-D atmospheric chemical transport model (GEOS-Chem), we quantify global and regional NF3 emission from 2015 to 2021. We find that global emissions have grown from 1.93 +/- 0.58 Gg yr(-1) (+/- one standard deviation) in 2015 to 3.38 +/- 0.61 Gg yr(-1) in 2021, with an average annual increase of 10% yr(-1). The available observations allow us to attribute significant emissions to China (0.93 +/- 0.15 Gg yr(-1) in 2015 and 1.53 +/- 0.20 Gg yr(-1) in 2021) and South Korea (0.38 +/- 0.07 Gg yr-1 to 0.65 +/- 0.10 Gg yr(-1)). East Asia contributes around 73% of the global NF3 emission increase from 2015 to 2021: approximately 41% of the increase is from emissions from China (with Taiwan included), 19% from South Korea, and 13% from Japan. For Japan, which is the only one of these three countries to submit annual NF3 emissions to UNFCCC, our bottom-up and top-down estimates are higher than reported. With increasing demand for electronics, especially flat panel displays, emissions are expected to further increase in the future.

Sulfur hexafluoride (SF 6 ) is a potent greenhouse gas. Here we use long-term atmospheric observations to determine SF 6 emissions from China between 2011 and 2021, which are used to evaluate the Chinese national SF 6 emission inventory and to better understand the global SF 6 budget. SF 6 emissions in China substantially increased from 2.6 (2.3-2.7, 68% uncertainty) Gg yr −1 in 2011 to 5.1 (4.8-5.4) Gg yr −1 in 2021. The increase from China is larger than the global total emissions rise, implying that it has offset falling emissions from other countries. Emissions in the less-populated western regions of China, which have potentially not been well quantified in previous measurement-based estimates, contribute significantly to the national SF 6 emissions, likely due to substantial power generation and transmission in that area. The CO 2 -eq emissions of SF 6 in China in 2021 were 125 (117-132) million tonnes (Mt), comparable to the national total CO 2 emissions of several countries such as the Netherlands or Nigeria. The increasing SF 6 emissions offset some of the CO 2 reductions achieved through transitioning to renewable energy in the power industry, and might hinder progress towards achieving China’s goal of carbon neutrality by 2060 if no concrete control measures are implemented.

According to the Montreal Protocol, the production and consumption of ozone-layer-depleting CCl 4 for dispersive applications was globally phased out by 2010, including China. However, continued CCl 4 emissions were disclosed, with the latest CCl 4 emissions unknown in eastern China. In the current study, based on the atmospheric measurements of ~12,000 air samples taken at two sites in eastern China, the 2021–2022 CCl 4 emissions are quantified as 7.6 ± 1.7 gigagrams per year. This finding indicates that CCl 4 emissions continued after being phased out for dispersive uses in 2010. Subsequently, our study identifies potential industrial sources (manufacture of general purpose machinery and manufacture of raw chemical materials, and chemical products) of CCl 4 emissions.

We use a process-based biogeochemistry model to simulate the fire impacts on soil thermal and hydrological dynamics and carbon budget of forest ecosystems in Northern Eurasia during 2003–2016 based on satellite-derived burn severity data. We find that burn severity generally increases in this region during the study period. Simulations indicate that fires increase soil temperature by 0.2–0.5°C through removing the ground moss and surface soil organic matter, especially in Asian part of the region. Fires also increase water runoff by about 37 km3 yr− 1 through reducing post-fire evapotranspiration, leading to a higher regional river discharge. Fires remove 1.7 Pg C of ecosystem carbon through combustion emissions during this period and reduce net ecosystem production from 106.4 to 66.1 Tg C yr− 1. Fires lead the forest ecosystems to lose 2.3 Pg C, shifting the forests from a carbon sink to a source in this period. Our study highlights the importance of wildfires in affecting soil thermal and hydrological and carbon dynamics in boreal forests.

Rapid growth in the emissions of nitrogen trifluoride (NF3), a potent greenhouse gas, poses a threat to the environment and the climate system. This study estimated NF3 emissions and their spatial distribution in China from 2017 to 2021 based on atmospheric observations from nine background stations in China, by employing a Lagrangian-dispersion-model-based Bayesian inversion technique. We found that NF3 emissions in China increased from 0.95 (0.82-1.07) Gg yr(-1) in 2017 to 1.41 (1.28-1.55) Gg yr(-1 )in 2021, representing a substantial growth of 48% over this period. The absolute increase in NF3 emissions in China over 2017-2020, 0.65 (0.57-0.74) Gg yr(-1) is comparable to the increase in global emissions (0.63 (0.50-0.75) Gg yr(-1)) over the same period. We identified substantial NF3 emissions in the Pearl and Yangtze River Delta regions and Hubei Province, where well-established semiconductor industries could have contributed to NF3 emissions. Moreover, large NF3 emissions were identified in northern China, including Hebei, Henan, and Shandong Provinces. If control measures are not implemented, increasing NF3 emissions may delay China's progress toward achieving its carbon neutrality target by 2060.

Methyl bromide (CH3Br) is an important ozone-depleting substance whose use is regulated under the Montreal Protocol. Quantifying emissions on the national scale is required to assess compliance with the Montreal Protocol and thereby ensure the timely recovery of the ozone layer. However, the spatial-temporal patterns of China's national CH3Br emissions remain unclear. Here we estimate the national emissions of CH3Br in China during 2011-2020 using atmospheric observations at 10 sites across China combined with an inversion technique (top-down) and compare those with an updated inventory of identified emission sources (bottom-up). Measured CH3Br mole fractions are enhanced well above the background mole fractions, especially at sites in eastern China. Top-down emission estimates exceed bottom-up estimates by 5.5 +/- 1.4 gigagrams per year, with the largest fraction (60%) of observationally derived CH3Br emissions arising from underestimated or unidentified emissions sources. This study shows the potential impacts of the unaccounted emissions on stratospheric ozone depletion, with implications for the Montreal Protocol. Methyl bromide (CH3Br) is an important ozone-depleting substance whose use is regulated under the Montreal Protocol. However, the spatial-temporal patterns of China's national CH3Br emissions remain unclear. Here, the authors find that China's top-down emission estimates exceed bottom-up estimates by 60%.

The perfluorocarbons tetrafluoromethane (CF4, PFC-14) and hexafluoroethane (C2F6, PFC-116) are potent greenhouse gases with near-permanent atmospheric lifetimes relative to human timescales and global warming potentials thousands of times that of CO2. Using long-term atmospheric observations from a Chinese network and an inverse modeling approach (top-down method), we determined that CF4 emissions in China increased from 4.7 (4.2-5.0, 68% uncertainty interval) Gg y(-1) in 2012 to 8.3 (7.7-8.9) Gg y(-1) in 2021, and C2F6 emissions in China increased from 0.74 (0.66-0.80) Gg y(-1) in 2011 to 1.32 (1.24-1.40) Gg y(-1) in 2021, both increasing by approximately 78%. Combined emissions of CF4 and C2F6 in China reached 78 Mt CO2-eq in 2021. The absolute increase in emissions of each substance in China between 2011-2012 and 2017-2020 was similar to (for CF4), or greater than (for C2F6), the respective absolute increase in global emissions over the same period. Substantial CF4 and C2F6 emissions were identified in the less-populated western regions of China, probably due to emissions from the expanding aluminum industry in these resource-intensive regions. It is likely that the aluminum industry dominates CF4 emissions in China, while the aluminum and semiconductor industries both contribute to C2F6 emissions. Based on atmospheric observations, this study validates the emission magnitudes reported in national bottom-up inventories and provides insights into detailed spatial distributions and emission sources beyond what is reported in national bottom-up inventories.