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Continued increase of CFC-113a (CCl3CF3) mixing ratios in the global atmosphere: emissions, occurrence and potential sources

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Brenninkmeijer,  Carl A. M.
Atmospheric Chemistry, Max Planck Institute for Chemistry, Max Planck Society;

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Citation

Adcock, K. E., Reeves, C. E., Gooch, L. J., Elvidge, E. C. L., Ashfold, M. J., Brenninkmeijer, C. A. M., et al. (2018). Continued increase of CFC-113a (CCl3CF3) mixing ratios in the global atmosphere: emissions, occurrence and potential sources. Atmospheric Chemistry and Physics, 18(7), 4737-4751. doi:10.5194/acp-18-4737-2018.


Cite as: http://hdl.handle.net/21.11116/0000-0001-A94A-E
Abstract
Atmospheric measurements of the ozone-depleting substance CFC-113a (CCl3CF3) are reported from ground-based stations in Australia, Taiwan, Malaysia and the United Kingdom, together with aircraft-based data for the upper troposphere and lower stratosphere. Building on previous work, we find that, since the gas first appeared in the atmosphere in the 1960s, global CFC-113a mixing ratios have been increasing monotonically to the present day. Mixing ratios of CFC-113a have increased by 40% from 0.50 to 0.70ppt in the Southern Hemisphere between the end of the previously published record in December 2012 and February 2017. We derive updated global emissions of 1.7Ggyr−1 on average between 2012 and 2016 using a two-dimensional model. We compare the long-term trends and emissions of CFC-113a to those of its structural isomer, CFC-113 (CClF2CCl2F), which still has much higher mixing ratios than CFC-113a, despite its mixing ratios and emissions decreasing since the 1990s. The continued presence of northern hemispheric emissions of CFC-113a is confirmed by our measurements of a persistent interhemispheric gradient in its mixing ratios, with higher mixing ratios in the Northern Hemisphere. The sources of CFC-113a are still unclear, but we present evidence that indicates large emissions in East Asia, most likely due to its use as a chemical involved in the production of hydrofluorocarbons. Our aircraft data confirm the interhemispheric gradient as well as showing mixing ratios consistent with ground-based observations and the relatively long atmospheric lifetime of CFC-113a. CFC-113a is the only known CFC for which abundances are still increasing substantially in the atmosphere.