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Carbon tetrachloride (CCl4) is an ozone-depleting substance, accounting for about 10% of the chlorine in the troposphere. Under the terms of the Montreal Protocol, its production for dispersive uses was banned from 2010. In this work we show that, despite the controls on production being introduced, CCl4 emissions from the eastern part of China did not decline between 2009 and 2016. This finding is in contrast to a recent bottom-up estimate, which predicted a significant decrease in emissions after the introduction of production controls. We find eastern Asian emissions of CCl4 to be 16 (9-24) Gg/year on average between 2009 and 2016, with the primary source regions being in eastern China. The spatial distribution of emissions that we derive suggests that the source distribution of CCl4 in China changed during the 8-year study period, indicating a new source or sources of emissions from China's Shandong province after 2012.

The perfluorocarbons tetrafluoromethane (CF 4 , PFC-14) and hexafluoroethane (C 2 F 6 , PFC-116) are potent greenhouse gases with near-permanent atmospheric lifetimes relative to human timescales and global warming potentials thousands of times that of CO 2 . Using long-term atmospheric observations from a Chinese network and an inverse modeling approach (top-down method), we determined that CF 4 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 C 2 F 6 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 CF 4 and C 2 F 6 in China reached 78 Mt CO 2 -eq in 2021. The absolute increase in emissions of each substance in China between 2011-2012 and 2017-2020 was similar to (for CF 4 ), or greater than (for C 2 F 6 ), the respective absolute increase in global emissions over the same period. Substantial CF 4 and C 2 F 6 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 CF 4 emissions in China, while the aluminum and semiconductor industries both contribute to C 2 F 6 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., Competing Interests: Competing interests statement:The authors declare no competing interest.

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., (© 2024. The Author(s).)

Emissions of chloroform (CHCl 3 ), a short-lived halogenated substance not currently controlled under the Montreal Protocol on Substances that Deplete the Ozone Layer, are offsetting some of the achievements of the Montreal Protocol. In this study, emissions of CHCl 3 from China were derived by atmospheric measurement-based "top-down" inverse modeling and a sector-based "bottom-up" inventory method. Top-down CHCl 3 emissions grew from 78 (72-83) Gg yr -1 in 2011 to a maximum of 193 (178-204) Gg yr -1 in 2017, followed by a decrease to 147 (138-154) Gg yr -1 in 2018, after which emissions remained relatively constant through 2020. The changes in emissions from China could explain all of the global changes during the study period. The CHCl 3 emissions in China were dominated by anthropogenic sources, such as byproduct emissions during disinfection and leakage from chloromethane industries. Had emissions continued to grow at the rate observed up to 2017, a delay of several years in Antarctic ozone layer recovery could have occurred. However, this delay will be largely avoided if global CHCl 3 emissions remain relatively constant in the future, as they have between 2018 and 2020.

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% (CH 2 Cl 2 ) to 81% (CF 3 Cl, 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 CO 2 -equivalent (CO 2 -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, SF 6 accounted for the highest proportion of CO 2 -equiv emissions (24%), followed by HFC-23 (22%), HFC-125 (17%), HFC-134a (13%), NF 3 (10%), CF 4 (5.9%), HFC-143a (3.9%), HFC-32 (3.4%), and HFC-152a (0.2%).

Methane (CH 4 ) mole fractions from the large semiseasonal Llanos de Moxos wetlands (∼70,000 km 2 ) in northern Bolivia were measured by aircraft flights and ground sampling during early March 2019 (late wet season). Daily fluxes of CH 4 determined from the measurements using box models and inverse modeling were between 168 (± 50) and 456 (± 145) mg CH 4 ⋅m -2 ⋅d -1 for the areas overflown, very high compared with those of previous Amazon basin studies. If the seasonality of the CH 4 emissions is comparable to other parts of the Amazon Basin, the region could contribute as much as 8% of annual Amazonian CH 4 emissions.

We report methane isotopologue data from aircraft and ground measurements in Africa and South America. Aircraft campaigns sampled strong methane fluxes over tropical papyrus wetlands in the Nile, Congo and Zambezi basins, herbaceous wetlands in Bolivian southern Amazonia, and over fires in African woodland, cropland and savannah grassland. Measured methane δ 13 C CH 4 isotopic signatures were in the range -55 to -49‰ for emissions from equatorial Nile wetlands and agricultural areas, but widely -60 ± 1‰ from Upper Congo and Zambezi wetlands. Very similar δ 13 C CH 4 signatures were measured over the Amazonian wetlands of NE Bolivia (around -59‰) and the overall δ 13 C CH 4 signature from outer tropical wetlands in the southern Upper Congo and Upper Amazon drainage plotted together was -59 ± 2‰. These results were more negative than expected. For African cattle, δ 13 C CH 4 values were around -60 to -50‰. Isotopic ratios in methane emitted by tropical fires depended on the C3 : C4 ratio of the biomass fuel. In smoke from tropical C3 dry forest fires in Senegal, δ 13 C CH 4 values were around -28‰. By contrast, African C4 tropical grass fire δ 13 C CH 4 values were -16 to -12‰. Methane from urban landfills in Zambia and Zimbabwe, which have frequent waste fires, had δ 13 C CH 4 around -37 to -36‰. These new isotopic values help improve isotopic constraints on global methane budget models because atmospheric δ 13 C CH 4 values predicted by global atmospheric models are highly sensitive to the δ 13 C CH 4 isotopic signatures applied to tropical wetland emissions. Field and aircraft campaigns also observed widespread regional smoke pollution over Africa, in both the wet and dry seasons, and large urban pollution plumes. The work highlights the need to understand tropical greenhouse gas emissions in order to meet the goals of the UNFCCC Paris Agreement, and to help reduce air pollution over wide regions of Africa. This article is part of a discussion meeting issue 'Rising methane: is warming feeding warming? (part 2)'.

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 (CH 2 Cl 2 ). 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 CH 2 Cl 2 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 CH 2 Cl 2 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 CH 2 Cl 2 emissions., (© 2021. The Author(s).)

We present the first spatially resolved distribution of the [Formula: see text] signature of wetland methane emissions and assess its impact on atmospheric [Formula: see text]. The [Formula: see text] signature map is derived by relating [Formula: see text] of precipitation to measured [Formula: see text] of methane wetland emissions at a variety of wetland types and locations. This results in strong latitudinal variation in the wetland [Formula: see text] source signature. When [Formula: see text] is simulated in a global atmospheric model, little difference is found in global mean, inter-hemispheric difference and seasonal cycle if the spatially varying [Formula: see text] source signature distribution is used instead of a globally uniform value. This is because atmospheric [Formula: see text] is largely controlled by OH fractionation. However, we show that despite these small differences, using atmospheric records of [Formula: see text] to infer changes in the wetland emissions distribution requires the use of the more accurate spatially varying [Formula: see text] source signature. We find that models will only be sensitive to changes in emissions distribution if spatial information can be exploited through the spatially resolved source signatures. In addition, we also find that on a regional scale, at sites measuring excursions of [Formula: see text] from background levels, substantial differences are simulated in atmospheric [Formula: see text] if using spatially varying or uniform source signatures. This article is part of a discussion meeting issue 'Rising methane: is warming feeding warming? (part 1)'.

Emissions of ozone-depleting substances, including trichlorofluoromethane (CFC-11), have decreased since the mid-1980s in response to the Montreal Protocol 1,2 . In recent years, an unexpected increase in CFC-11 emissions beginning in 2013 has been reported, with much of the global rise attributed to emissions from eastern China 3,4 . Here we use high-frequency atmospheric mole fraction observations from Gosan, South Korea and Hateruma, Japan, together with atmospheric chemical transport-model simulations, to investigate regional CFC-11 emissions from eastern China. We find that CFC-11 emissions returned to pre-2013 levels in 2019 (5.0 ± 1.0 gigagrams per year in 2019, compared to 7.2 ± 1.5 gigagrams per year for 2008-2012, ±1 standard deviation), decreasing by 10 ± 3 gigagrams per year since 2014-2017. Furthermore, we find that in this region, carbon tetrachloride (CCl 4 ) and dichlorodifluoromethane (CFC-12) emissions-potentially associated with CFC-11 production-were higher than expected after 2013 and then declined one to two years before the CFC-11 emissions reduction. This suggests that CFC-11 production occurred in eastern China after the mandated global phase-out, and that there was a subsequent decline in production during 2017-2018. We estimate that the amount of the CFC-11 bank (the amount of CFC-11 produced, but not yet emitted) in eastern China is up to 112 gigagrams larger in 2019 compared to pre-2013 levels, probably as a result of recent production. Nevertheless, it seems that any substantial delay in ozone-layer recovery has been avoided, perhaps owing to timely reporting 3,4 and subsequent action by industry and government in China 5,6 .

Unregulated chlorocarbons, here defined as dichloromethane (CH 2 Cl 2 ), perchloroethene (C 2 Cl 4 ), chloroform (CHCl 3 ), and methyl chloride (CH 3 Cl), are gases not regulated by the Montreal Protocol. While CH 3 Cl is the largest contributor of atmospheric chlorine, recent studies have shown that growth in emissions of the less abundant chlorocarbons could pose a significant threat to the recovery of the ozone layer. Despite this, there remain many regions for which no atmospheric monitoring exists, leaving gaps in our understanding of global emissions. Here, we report on a new time series of chlorocarbon measurements from Cape Point, South Africa for 2017, which represent the first published high-frequency measurements of these gases from Africa. For CH 2 Cl 2 and C 2 Cl 4 , the majority of mole fraction enhancements were observed from the north, consistent with anthropogenically modified air from Cape Town, while for CHCl 3 and CH 3 Cl, we found evidence for both oceanic and terrestrial sources. Using an inverse method, we estimated emissions for south-western South Africa (SWSA). For each chlorocarbon, SWSA accounted for less than 1% of global emissions. For CH 2 Cl 2 and C 2 Cl 4 , we extrapolated using population statistics and found South African emissions of 8.9 (7.4-10.4) Gg yr -1 and 0.80 (0.64-1.04) Gg yr -1 , respectively.

One hydrochlorofluorocarbon and two hydrofluorocarbons (HCFC-22, HFC-125, and HFC-152a) were measured in air samples at the Cape Point observatory (CPT), South Africa, during 2017. These data represent the first such atmospheric measurements of these compounds from southwestern South Africa (SWSA). Baseline atmospheric growth rates were estimated to be 8.36, 4.10, and 0.71 ppt year -1 for HCFC-22, HFC-125, and HFC-152a, respectively. The CPT measurements were combined with an inverse model to investigate emissions from SWSA. For all three halocarbons, Cape Town was found to be the dominant source within SWSA. These estimates were extrapolated, based on population statistics, to estimate emissions for the whole of South Africa. We estimate South Africa's 2017 emissions to be 3.0 (1.6-4.4), 0.8 (0.5-1.2), and 1.1 (0.6-1.6) Gg year -1 for HCFC-22, HFC-125, and HFC-152a, respectively. For all three halocarbons, South Africa's contribution to global emissions is small (<2.5%), but future monitoring is needed to ensure South Africa's compliance with regulation set out by the Montreal Protocol and its Amendments.

The recovery of the stratospheric ozone layer relies on the continued decline in the atmospheric concentrations of ozone-depleting gases such as chlorofluorocarbons 1 . The atmospheric concentration of trichlorofluoromethane (CFC-11), the second-most abundant chlorofluorocarbon, has declined substantially since the mid-1990s 2 . A recently reported slowdown in the decline of the atmospheric concentration of CFC-11 after 2012, however, suggests that global emissions have increased 3,4 . A concurrent increase in CFC-11 emissions from eastern Asia contributes to the global emission increase, but the location and magnitude of this regional source are unknown 3 . Here, using high-frequency atmospheric observations from Gosan, South Korea, and Hateruma, Japan, together with global monitoring data and atmospheric chemical transport model simulations, we investigate regional CFC-11 emissions from eastern Asia. We show that emissions from eastern mainland China are 7.0 ± 3.0 (±1 standard deviation) gigagrams per year higher in 2014-2017 than in 2008-2012, and that the increase in emissions arises primarily around the northeastern provinces of Shandong and Hebei. This increase accounts for a substantial fraction (at least 40 to 60 per cent) of the global rise in CFC-11 emissions. We find no evidence for a significant increase in CFC-11 emissions from any other eastern Asian countries or other regions of the world where there are available data for the detection of regional emissions. The attribution of any remaining fraction of the global CFC-11 emission rise to other regions is limited by the sparsity of long-term measurements of sufficient frequency near potentially emissive regions. Several considerations suggest that the increase in CFC-11 emissions from eastern mainland China is likely to be the result of new production and use, which is inconsistent with the Montreal Protocol agreement to phase out global chlorofluorocarbon production by 2010.

Changes in tropical wetland, ruminant or rice emissions are thought to have played a role in recent variations in atmospheric methane (CH 4 ) concentrations. India has the world's largest ruminant population and produces ~ 20% of the world's rice. Therefore, changes in these sources could have significant implications for global warming. Here, we infer India's CH 4 emissions for the period 2010-2015 using a combination of satellite, surface and aircraft data. We apply a high-resolution atmospheric transport model to simulate data from these platforms to infer fluxes at sub-national scales and to quantify changes in rice emissions. We find that average emissions over this period are 22.0 (19.6-24.3) Tg yr -1 , which is consistent with the emissions reported by India to the United Framework Convention on Climate Change. Annual emissions have not changed significantly (0.2 ± 0.7 Tg yr -1 ) between 2010 and 2015, suggesting that major CH 4 sources did not change appreciably. These findings are in contrast to another major economy, China, which has shown significant growth in recent years due to increasing fossil fuel emissions. However, the trend in a global emission inventory has been overestimated for China due to incorrect rate of fossil fuel growth. Here, we find growth has been overestimated in India but likely due to ruminant and waste sectors.India's methane emissions have been quantified using atmospheric measurements to provide an independent comparison with reported emissions. Here Ganesan et al. find that derived methane emissions are consistent with India's reports and no significant trend has been observed between 2010-2015.

The growth in global methane (CH 4 ) concentration, which had been ongoing since the industrial revolution, stalled around the year 2000 before resuming globally in 2007. We evaluate the role of the hydroxyl radical (OH), the major CH 4 sink, in the recent CH 4 growth. We also examine the influence of systematic uncertainties in OH concentrations on CH 4 emissions inferred from atmospheric observations. We use observations of 1,1,1-trichloroethane (CH 3 CCl 3 ), which is lost primarily through reaction with OH, to estimate OH levels as well as CH 3 CC 3 emissions, which have uncertainty that previously limited the accuracy of OH estimates. We find a 64-70% probability that a decline in OH has contributed to the post-2007 methane rise. Our median solution suggests that CH 4 emissions increased relatively steadily during the late 1990s and early 2000s, after which growth was more modest. This solution obviates the need for a sudden statistically significant change in total CH 4 emissions around the year 2007 to explain the atmospheric observations and can explain some of the decline in the atmospheric 13 CH 4 / 12 CH 4 ratio and the recent growth in C 2 H 6 Our approach indicates that significant OH-related uncertainties in the CH 4 budget remain, and we find that it is not possible to implicate, with a high degree of confidence, rapid global CH 4 emissions changes as the primary driver of recent trends when our inferred OH trends and these uncertainties are considered., Competing Interests: The authors declare no conflict of interest.

We infer global and regional emissions of five of the most abundant hydrofluorocarbons (HFCs) using atmospheric measurements from the Advanced Global Atmospheric Gases Experiment and the National Institute for Environmental Studies, Japan, networks. We find that the total CO2-equivalent emissions of the five HFCs from countries that are required to provide detailed, annual reports to the United Nations Framework Convention on Climate Change (UNFCCC) increased from 198 (175-221) Tg-CO2-eq ⋅ y(-1) in 2007 to 275 (246-304) Tg-CO2-eq ⋅ y(-1) in 2012. These global warming potential-weighted aggregated emissions agree well with those reported to the UNFCCC throughout this period and indicate that the gap between reported emissions and global HFC emissions derived from atmospheric trends is almost entirely due to emissions from nonreporting countries. However, our measurement-based estimates of individual HFC species suggest that emissions, from reporting countries, of the most abundant HFC, HFC-134a, were only 79% (63-95%) of the UNFCCC inventory total, while other HFC emissions were significantly greater than the reported values. These results suggest that there are inaccuracies in the reporting methods for individual HFCs, which appear to cancel when aggregated together.