The perfluorocarbons (PFCs), tetrafluoromethane (CF₄) and hexafluoroethane (C₂F₆), are potent greenhouse gases with very long atmospheric lifetimes. They are emitted almost entirely from industrial sources, including the aluminum and rare earth metal smelting industries that emit them as by-products, and the semiconductor and flat panel display manufacturing industries that use them and vent unutilized amounts to the atmosphere. Despite extensive industrial efforts to quantify and curb these emissions, "top-down" PFC emission estimates derived from atmospheric measurements continue to rise and are significantly greater than reported process- and inventory-based "bottom-up" emissions. In this study, we estimate emissions of CF₄ and C₂F₆ from East Asia, where PFC emitting industries are heavily concentrated, using a top-down approach (a Bayesian inversion) with high-frequency atmospheric measurements at Gosan (Jeju Island, South Korea) for 2008-2019. We also compile and analyze the available bottom-up CF₄ and C₂F₆ emissions in East Asia from industrial and government reports. Our results suggest that the observed increases in global PFC emissions since 2015 are driven primarily by China's aluminum industry, with significant contributions from Japan's and Korea's semiconductor industry. Our analysis suggests that Chinese emissions occur predominantly from the aluminum industry, although their emissions per production ratio may be improving. Our results for Japan and Korea find significant discrepancies between top-down and bottom-up emissions estimates, suggesting that the effectiveness of emission reduction systems (abatement) used in their semiconductor industries may be overestimated. Overall, our top-down results for East Asia contribute significantly to reducing the gap in the global PFC emission budgets.

Methyl bromide (CH3Br) is a potent ozone-depleting substance (ODS) that has both natural and anthropogenic sources. CH3Br has been used mainly for preplant soil fumigation, post-harvest grain and timber fumigation, and structural fumigation. Most non-quarantine and pre-shipment (non-QPS) uses were phased out by 2005 for non-Article 5 (developed) countries and by 2015 for Article 5 (developing) countries under the Montreal Protocol on Substances that Deplete the Ozone Layer; some uses have continued under critical-use exemptions (CUEs). Under the protocol, individual nations are required to report annual data on CH3Br production and consumption for quarantine-pre-shipment (QPS) uses, non-QPS uses, and CUEs to the United Nations Environment Programme (UNEP). In this study, we analyzed high-precision, in situ measurements of atmospheric mole fractions of CH3Br obtained at the Gosan station on Jeju Island, South Korea, from 2008 to 2019. The background mole fractions of CH3Br in the atmosphere at Gosan declined from 8.5±0.8gppt (parts per trillion) in 2008 to 7.4±0.6gppt in 2019 at a rate of -0.13±0.02gpptgyr-1. At Gosan, we also observed periods of persistent mole fractions (pollution events) elevated above the decreasing background in continental air masses from China. Statistical back-trajectory analyses showed that these pollution events are predominantly traced back to CH3Br emissions from eastern China. Using an interspecies correlation (ISC) method with the reference trace species CFC-11 (CCl3F), we estimate anthropogenic CH3Br emissions from eastern China at an average of 4.1±1.3gGggyr-1 in 2008-2019, approximately 2.9±1.3gGggyr-1 higher than the bottom-up emission estimates reported to UNEP. Possible non-fumigation CH3Br sources - rapeseed production and biomass burning - were assessed, and it was found that the discrepancy is most likely due to unreported or incorrectly reported QPS and non-QPS fumigation uses. These unreported anthropogenic emissions of CH3Br are confined to eastern China and account for 30g%-40g% of anthropogenic global CH3Br emissions. They are likely due to delays in the introduction of CH3Br alternatives, such as sulfuryl fluoride (SO2F2), heat, and irradiation, and a possible lack of industry awareness of the need for regulation of CH3Br production and use.

Abstract. We reconstruct atmospheric abundances of the potent greenhouse gas c-C4F8 (perfluorocyclobutane, perfluorocarbon PFC-318) from measurements of in situ, archived, firn, and aircraft air samples with precisions of ~ 1–2 % reported on the SIO-14 gravimetric calibration scale. Combined with inverse methods, we found near zero atmospheric abundances from the early 1900s to the early 1960s, after which they rose sharply, reaching 1.66 ppt (parts per trillion dry-air mole fraction) in 2017. Global c-C4F8 emissions rose from near zero in the 1960s to ~ 1.2 Gg yr−1 in the late 1970s to late 1980s, then declined to ~ 0.8 Gg yr−1 in the mid-1990s to early 2000s, followed by a rise since the early 2000s to ~ 2.2 Gg yr−1 in 2017. These emissions are significantly larger than inventory based emission estimates. Estimated emissions from eastern Asia rose from 0.36 Gg yr−1 in 2010 to 0.73 Gg yr−1 in 2016 and 2017, 31 % of global emissions, mostly from eastern China. We estimate emissions of 0.14 Gg yr−1 from Northern and Central India in 2016 and find evidence for significant emissions from Russia. In contrast, recent emissions from North Western Europe and Australia are estimated to be small (≤ 1 % each). We conclude that emissions from China, India and Russia are likely related to production of polytetrafluoroethylene (PTFE, “Teflon”) and other fluoropolymers that are based on the pyrolysis of hydrochlorofluorocarbon HCFC-22 (CHClF2) in which c-C4F8 is a known by-product. The semiconductor sector, where c-C4F8 is used, is estimated to be a small source. Without an obvious correlation with population density, incineration of waste containing fluoropolymers is probably a minor source, and we find no evidence of emissions from electrolytic production of aluminum in Australia. While many possible emissive uses of c-C4F8 are known, the start of significant emissions may well be related to the advent of commercial PTFE production in 1947. Process controls or abatement to reduce c-C4F8 by-product were probably not in place in the early decades, explaining the increase in emissions. With the advent of by-product reporting requirements to the United Nations Framework Convention on Climate Change (UNFCCC) in the 1990s, concern about climate change and product stewardship, abatement, and perhaps the collection of c-C4F8 by-product for use in the semiconductor industry where it can be easily abated, it is conceivable that emissions in developed countries were stabilized and then reduced, explaining the observed emission reduction in the 1980s and 1990s. Concurrently, production of PTFE in China began to increase rapidly. Without emission reduction requirements, it is plausible that global emissions today are dominated by China and other developing countries, in agreement with our analysis. We predict that c-C4F8 emissions will continue to rise and that c-C4F8 will become the second most important emitted PFC in terms of CO2-equivalent emissions within a year or two. The 2017 radiative forcing of c-C4F8 (0.52 mW m−2) is small but emissions of c-C4F8 and other PFCs, due to their very long atmospheric lifetimes, essentially permanently alter Earth's radiative budget and should be reduced. Significant emissions outside of the investigated regions clearly show that observational capabilities and reporting requirements need to be improved to understand global and country scale emissions of PFCs and other synthetic greenhouse gases and ozone depleting substances.

We reconstruct atmospheric abundances of the potent greenhouse gas span classCombining double low line inline-formula span classCombining double low line inline-formula perfluorocyclobutane, perfluorocarbon PFC-318) from measurements of in situ, archived, firn, and aircraft air samples with precisions of span classCombining double low line inline-formula reported on the SIO-14 gravimetric calibration scale. Combined with inverse methods, we found near-zero atmospheric abundances from the early 1900s to the early 1960s, after which they rose sharply, reaching 1.66ppt (parts per trillion dry-air mole fraction) in 2017. Global span classCombining double low line inline-formula span classCombining double low line inline-formula emissions rose from near zero in the 1960s to span classCombining double low line inline-formula (1span classCombining double low line inline-formula gyrspan classCombining double low line inline-formula in the late 1970s to late 1980s, then declined to span classCombining double low line inline-formula classCombining double low line inline-formula in the mid-1990s to early 2000s, followed by a rise since the early 2000s to span classCombining double low line inline-formula 2.20±0.05 Ggyrspan classCombining double low line inline-formula in 2017. These emissions are significantly larger than inventory-based emission estimates. Estimated emissions from eastern Asia rose from 0.36Ggyrspan classCombining double low line inline-formula in 2010 to 0.73Ggyrspan classCombining double low line inline-formula in 2016 and 2017, 31% of global emissions, mostly from eastern China. We estimate emissions of 0.14Ggyrspan classCombining double low line inline-formula from northern and central India in 2016 and find evidence for significant emissions from Russia. In contrast, recent emissions from northwestern Europe and Australia are estimated to be small (span classCombining double low line inline-formula % each). We suggest that emissions from China, India, andspan idCombining double low line page10336 Russia are likely related to production of polytetrafluoroethylene (PTFE, Teflon ) and other fluoropolymers and fluorochemicals that are based on the pyrolysis of hydrochlorofluorocarbon HCFC-22 (span classCombining double low line inline-formula) in which span classCombining double low line inline-formula classCombining double low line inline-formula is a known by-product. The semiconductor sector, where span classCombining double low line inline-formula span classCombining double low line inline-formula is used, is estimated to be a small source, at least in South Korea, Japan, Taiwan, and Europe. Without an obvious correlation with population density, incineration of waste-containing fluoropolymers is probably a minor source, and we find no evidence of emissions from electrolytic production of aluminum in Australia. While many possible emissive uses of span classCombining double low line inline-formula span classCombining double low line inline-formula are known and though we cannot categorically exclude unknown sources, the start of significant emissions may well be related to the advent of commercial PTFE production in 1947. Process controls or abatement to reduce the span classCombining double low line inline-formula span classCombining double low line inline-formula by-product were probably not in place in the early decades, explaining the increase in emissions in the 1960s and 1970s. With the advent of by-product reporting requirements to the United Nations Framework Convention on Climate Change (UNFCCC) in the 1990s, concern about climate change and product stewardship, abatement, and perhaps the collection of span classCombining double low line inline-formula span classCombining double low line inline-formula by-product for use in the semiconductor industry where it can be easily abated, it is conceivable that emissions in developed countries were stabilized and then reduced, explaining the observed emission reduction in the 1980s and 1990s. Concurrently, production of PTFE in China began to increase rapidly. Without emission reduction requirements, it is plausible that global emissions today are dominated by China and other developing countries. We predict that span classCombining double low line inline-formula span classCombining double low line inline-formula emissions will continue to rise and that span classCombining double low line inline-formula span classCombining double low line inline-formula will become the second most important emitted PFC in terms of span classCombining double low line inline-formula equivalent emissions within a year or two. The 2017 radiative forcing of span classCombining double low line inline-formula span classCombining double low line inline-formula 0.52mWmspan classCombining double low line inline-formula) is small but emissions of span classCombining double low line inline-formula span classCombining double low line inline-formula and other PFCs, due to their very long atmospheric lifetimes, essentially permanently alter Earth's radiative budget and should be reduced. Significant emissions inferred outside of the investigated regions clearly show that observational capabilities and reporting requirements need to be improved to understand global and country-scale emissions of PFCs and other synthetic greenhouse gases and ozone-depleting substances.