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 0.70 ppt in the Southern Hemisphere between the end of the previously published record in December 2012 and February 2017. We derive updated global emissions of 1.7 Gg yrĝ'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.
| Original language | English |
|---|---|
| Pages (from-to) | 4737-4751 |
| Number of pages | 15 |
| Journal | Atmospheric Chemistry and Physics |
| Volume | 18 |
| Issue number | 7 |
| DOIs | |
| Publication status | Published - 9 Apr 2018 |
Funding
Acknowledgements. We are grateful for the work of the Geo-physica team, the CARIBIC team (CARIBIC-IAGOS), the staff at the Cape Grim station, the NOAA Global Monitoring Division and the AGAGE network. The StratoClim flights were funded by the European Commission (FP7 project Stratoclim-603557, www.stratoclim.org). The collection and curation of the Cape Grim Air Archive is jointly funded by CSIRO, the Bureau of Meteorology (BoM) and Refrigerant Reclaim Australia; BoM/CGBAPS staff at Cape Grim were/are largely responsible for the collection of archive samples and UEA flask air samples; the original (mid-1990s) subsampling of the archive for UEA was funded by AFEAS and CSIRO, with ongoing subsampling by CSIRO. Karina E. Adcock was supported by the UK Natural Environment Research Council (PhD studentship NE/L002582/1). Johannes C. Laube received funding from the UK Natural Environment Research Council (Research Fellowship NE/I021918/1). Norfazrin Mohd Hanif has been funded through a PhD studentship by the Ministry of Education Malaysia (MOE) and Universiti Kebangsaan Malaysia (UKM). We acknowledge use of the NAME atmospheric dispersion model and associated NWP meteorological datasets made available to us by the UK Met Office. We also acknowledge the significant storage resources and analysis facilities made available to us on JASMIN by STFC CEDA along with the corresponding support teams.