Trends and emissions of six perfluorocarbons in the Northern Hemisphere and Southern Hemisphere

Abstract

Abstract. Perfluorocarbons (PFCs) are potent greenhouse gases with global warming potentials up to several thousand times greater than CO2 on a 100-year time horizon. The lack of any significant sinks for PFCs means that they have long atmospheric lifetimes of the order of thousands of years. Anthropogenic production is thought to be the only source for most PFCs. Here we report an update on the global atmospheric abundances of the following PFCs, most of which have for the first time been analytically separated according to their isomers: c-octafluorobutane (c-C4F8), n-decafluorobutane (n-C4F10), n-dodecafluoropentane (n-C5F12), n-tetradecafluorohexane (n-C6F14), and n-hexadecafluoroheptane (n-C7F16). Additionally, we report the first data set on the atmospheric mixing ratios of perfluoro-2-methylpentane (i-C6F14). The existence and significance of PFC isomers have not been reported before, due to the analytical challenges of separating them. The time series spans a period from 1978 to the present. Several data sets are used to investigate temporal and spatial trends of these PFCs: time series of air samples collected at Cape Grim, Australia, from 1978 to the start of 2018; a time series of air samples collected between July 2015 and April 2017 at Tacolneston, UK; and intensive campaign-based sampling collections from Taiwan. Although the remote “background” Southern Hemispheric Cape Grim time series indicates that recent growth rates of most of these PFCs are lower than in the 1990s, we continue to see significantly increasing mixing ratios that are between 6 % and 27 % higher by the end of 2017 compared to abundances measured in 2010. Air samples from Tacolneston show a positive offset in PFC mixing ratios compared to the Southern Hemisphere baseline. The highest mixing ratios and variability are seen in air samples from Taiwan, which is therefore likely situated much closer to PFC sources, confirming predominantly Northern Hemispheric emissions for most PFCs. Even though these PFCs occur in the atmosphere at levels of parts per trillion molar or less, their total cumulative global emissions translate into 833 million metric tonnes of CO2 equivalent by the end of 2017, 23 % of which has been emitted since 2010. Almost two-thirds of the CO2 equivalent emissions within the last decade are attributable to c-C4F8, which currently also has the highest emission rates that continue to grow. Sources of all PFCs covered in this work remain poorly constrained and reported emissions in global databases do not account for the abundances found in the atmosphere.

Revealing the global emission gaps for fully fluorinated greenhouse gases

“…However, some slight emission gaps for global c -C 4 F 8 results were found before 2000. The average c -C 4 F 8 emissions from Droste et al, 2020 26 (15 Mt CO 2 -eq yr −1 over 1985–1988) and Oram et al, 2012 25 (15 Mt CO 2 -eq yr −1 over 1985–1988) were slightly higher than those from Mühle et al, 2019 24 [12 Mt CO 2 -eq yr −1 over 1985–1988 in CSIRO Inversion; 12 Mt CO 2 -eq yr −1 over 1985–1988 in Bristol Inversion], while c -C 4 F 8 emissions (1991–1998) from Droste et al, 2020 26 (5 Mt CO 2 -eq yr −1 ) and Oram et al, 2012 25 (5 Mt CO 2 -eq yr −1 ) were slightly lower than results of around 8 Mt CO 2 -eq yr −1 from both Mühle et al, 2019 24 and Mühle et al, 2022 23 . The c -C 4 F 8 datasets from more than one station (including Zeppelin, Mace Head, Jungfraujoch, Monte Cimone, Trinidad Head, Shangdianzi, Gosan, La Jolla, Ragged Point and so on) were employed in other studies 23 , 24 to derive c -C 4 F 8 emissions, while Oram et al, 2012 25 only used the c -C 4 F 8 dataset from Cape Grim to obtain the global TD c -C 4 F 8 emissions, which may explain the larger variability of its results.…”

Indicators of Global Climate Change 2023: annual update of key indicators of the state of the climate system and human influence

“…In cases where no updated information is available, global estimates were extrapolated from Vimont et al (2022), Western et al (2023) or other literature and were scaled to be consistent with those reported in AR6. Some extrapolations are based on data from the mid-2010s (Droste et al, 2020;Laube et al, 2014;Simmonds et al, 2017;Vollmer et al, 2018) but have an imperceptible effect on the total ERF assessed in Sect. 4 and are included to maintain consistency with AR6.…”

Indicators of Global Climate Change 2023: annual update of key indicators of the state of the climate system and human influence

“…In cases where no updated information is available, global estimates were extrapolated from Vimont et al (2022), Western et al (2023), or other literature and scaled to be consistent with those reported in AR6. Some extrapolations are based on data from the mid-2010s (Droste et al, 2020;Laube et al, 2014;Simmonds et al, 2017;Vollmer et al, 2018), but have an imperceptible effect on the total ERF assessed in Sect. 4, and are included to maintain consistency with AR6.…”