Abstract
Abstract. The detection of increasing global CFC-11 emissions after 2012 alerted society to a possible violation of the Montreal Protocol on Substances that Deplete the Ozone Layer (MP). This alert resulted in parties to the MP taking urgent actions. As a result, atmospheric measurements made in 2019 suggest a sharp decline in global CFC-11 emissions. Despite the success in the detection and mitigation of part of this problem, regions fully responsible for the recent global emission changes in 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 the decline between 2014–2017 and 2019 were explained by regional emission changes in eastern mainland China. Here, we used atmospheric CFC-11 measurements made from two global aircraft surveys – the HIAPER (High-performance Instrumented Airborne Platform for Environmental Research) 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 US National Oceanic and Atmospheric Administration during these two periods – to derive global and regional emission changes in 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, 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. The atmospheric observations further 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 southern hemispheric lands were not likely due to the observed increase of north-to-south interhemispheric gradients in atmospheric CFC-11 mole fractions from 2012–2017.
Highlights
Trichlorofluoromethane, CFC-11, is a potent ozone depleting substance, whose production has been controlled by the Montreal Protocol (MP) since 1987
The other nine prior emission fields were constructed like the first a priori field but with an additional 20 Gg yr−1 of emissions imposed over North America, South America, Africa, Europe, Australia, boreal Asia, temperate eastern Asia, temperate western Asia, and tropical Asia
Besides at the Earth’s surface, a similar magnitude of this slowdown in atmospheric CFC-11 mole fraction decline is apparent throughout the free troposphere in the aircraft profiles obtained during the HIPPO and Atmospheric Tomography Mission (ATom) campaigns, each of which involved sampling deployments spread over approximately 2 years (Fig. 4)
Summary
Trichlorofluoromethane, CFC-11, is a potent ozone depleting substance, whose production has been controlled by the Montreal Protocol (MP) since 1987. A large increase in global CFC-11 emissions from 2012–2017 was discovered (Montzka et al, 2018; Rigby et al, 2019; Montzka et al, 2021), suggesting illicit CFC-11 production despite the global ban on production and consumption under the MP beginning in 2010. Despite the international effort to understand the origin of this large global emission increase in CFC-11, only a portion of the emission rise (60 ± 40 %) could be explained by emission increases from eastern mainland China (Rigby et al, 2019; Adcock et al, 2020; Park et al, 2021). It remains unclear where the rest of the global CFC-11 emission increase originated. We further investigate regional contributions to the global CFC-11 emission rise between these two periods
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