29 Sep 2021

29 Sep 2021

Review status: this preprint is currently under review for the journal ACP.

Continental-scale contributions to the global CFC-11 emission increase between 2012 and 2017

Lei Hu1,2, Stephen Montzka2, Fred Moore1,2, Eric Hintsa1,2, Geoff Dutton1,2, M. Carolina Siso1,2, Kirk Thoning2, Robert Portmann3, Kathryn McKain1,2, Colm Sweeney2, Isaac Vimont1,2, David Nance1,2, Bradley Hall2, and Steven Wofsy4 Lei Hu et al.
  • 1Cooperative Institute for Research in Environmental Sciences, University of Colorado-Boulder, CO, USA
  • 2Global Monitoring Laboratory, NOAA, Boulder, CO, USA
  • 3Chemical Science Laboratory, NOAA, Boulder, CO, USA
  • 4Department of Earth and Planetary Sciences, Harvard University, Boston, MA, USA

Abstract. The early detection of a global emission increase of CFC-11 after 2012 (Montzka et al., 2018) alerted society to a possible violation of the Montreal Protocol on Substances that Deplete the Ozone Layer (MP). This early alert resulted in parties participating in the MP taking urgent actions (United Nations Environment Programme (UNEP), 2019). As a result, atmospheric measurements made in 2019 suggest a sharp decline in global CFC-11 emissions (Montzka et al., 2021). Despite the success in the early detection and mitigation of some of this problem, regions fully responsible for the recent global emission changes of CFC-11 have not yet been identified. Roughly two thirds (60 ± 40 %) of the emission increase between 2008–2012 and 2014–2017 and two thirds (60 ± 30 %) of emission decline between 2014–2017 and 2019 was explained by regional emission changes in eastern mainland China (Park et al., 2021; Rigby et al., 2019). Here, we used atmospheric CFC-11 measurements made from two global aircraft surveys, the HIAPER Pole-to-Pole Observations (HIPPO) in November 2009–September 2011 and the Atmospheric Tomography Mission (ATom) in August 2016–May 2018, in combination with the global CFC-11 measurements made by the U.S. National Oceanic and Atmospheric Administration during these two periods, to derive global and regional emission changes of CFC-11. Our results suggest Asia accounted for the largest fractions of global CFC-11 emissions in both periods, 43 (37–52) % during November 2009–September 2011 and 57 (49–62) % during August 2016–May 2018. Asia was also primarily responsible for the emission increase between these two periods, accounting for 86 (59–115) % of the global CFC-11 emission rise between the two periods. Besides eastern mainland China, we find that temperate western Asia and tropical Asia also contributed significantly to global CFC-11 emissions during both periods and likely to the global CFC-11 emission increase between these periods. Besides Asia, the atmospheric observations also provide strong constraints on CFC-11 emissions from North America and Europe, suggesting that each of them accounted for 10–15 % of global CFC-11 emissions during the HIPPO period and smaller fractions in the ATom period. For South America, Africa, and Australia, the derived regional emissions had larger dependence on the prior assumptions of emissions and emission changes, due to a lower sensitivity of the observations considered here to emissions from these regions. However, significant increases in CFC-11 emissions from the southern hemispheric lands were not likely due to the observed increase of north-to-south interhemispheric gradients in atmospheric CFC-11 mole fractions from 2012 to 2017.

Lei Hu et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-793', Anonymous Referee #1, 08 Oct 2021
  • RC2: 'Comment on acp-2021-793', Anonymous Referee #2, 21 Nov 2021

Lei Hu et al.


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Short summary
The unexpected increase of CFC-11 emissions between 2012 and 2017 resulted in concerns on delaying the stratospheric ozone recovery. Although the subsequent decline of CFC-11 emissions indicated a mitigation in some of this problem, regions fully responsible for these large emission changes were unclear. Here, our new estimate, based on atmospheric measurements from two global campaigns and from NOAA, suggest Asia primarily contributed to the global CFC-11 emission rise during 2012–2017.