Joint inference of CFC lifetimes and banks suggests previously unidentified emissions

Abstract

Chlorofluorocarbons (CFCs) are harmful ozone depleting substances and greenhouse gases. CFC production was phased-out under the Montreal Protocol, however recent studies suggest new and unexpected emissions of CFC-11. Quantifying CFC emissions requires accurate estimates of both atmospheric lifetimes and ongoing emissions from old equipment (i.e. ‘banks’). In a Bayesian framework we simultaneously infer lifetimes, banks and emissions of CFC-11, 12 and 113 using available constraints. We find that lifetimes of all three gases are likely shorter than previous estimates, suggesting that best estimates of inferred emissions are larger than recent evaluations. Our analysis indicates that bank emissions are decreasing faster than inferred emissions, and we estimate new, unexpected emissions during 2014-2016 were 19.6, 16.2, and 7.7 Gg/yr for CFC-11, 12 and 113, respectively. While recent studies have focused on unexpected CFC-11 emissions, our results call for further investigation of potential sources of emissions of CFC-12 and CFC-113, along with CFC-11.

Quantifying the Imprints of Stratospheric Contributions to Interhemispheric Differences in Tropospheric CFC‐11, CFC‐12, and N2O Abundances

“…This suggests that emission anomalies are likely less pronounced relative to stratospheric influences for N 2 O compared to CFC-11 and CFC-12 over this time period. In other words, N 2 O observations exhibit similar correlations between the stratosphere and troposphere as WACCM simulations, whereas CFC-11 and CFC-12 do not; we interpret this to support earlier work that identifies new and unexpected emissions of CFC-11 after 2012 (Montzka et al, 2018;Rigby et al, 2019), and also to a lesser extent for CFC-12 (Lickley et al, 2021;Park et al, 2021). We note, however, that decoupling between the stratospheric and tropospheric anomalies are less pronounced after 2012 for CFC-12 such that the present study cannot identify the timing and occurrence of anomalous CFC-12 emissions.…”

“…Emissions can be inferred from observed changes in atmospheric mole fractions along with an assumed atmospheric lifetime (WMO, 2003(WMO, , 2018. However, sparse networks of in situ trace gas measurements together with large uncertainties in atmospheric lifetimes (Ko et al, 2013) can lead to large uncertainties in inferred emissions (Lickley, 2021). Experts have long looked to hemispheric differences in mole fractions of these chemicals as evidence to support conclusions about changes in anthropogenic emissions (Lovelock et al, 1973).…”

Phase Unlocking and the Modulation of Tropopause‐Level Trace Gas Advection by the Quasibiennial Oscillation

“…Recent detection of an unexpected uptick in emissions (and possible illegal production) of the ozone‐depleting substance trichlorofluoromethane (CFC‐11) led to efforts to curb anthropogenic emissions, resulting in a robust and sharp decline in global CFC‐11 emissions in 2019–2020 (Montzka et al., 2018, 2021). With just 40%–60% of unexpected emissions attributed to eastern China 2014–2017 (Rigby et al., 2019) and with a detected decline over 2017–2018 in Chinese CFC‐11 production (Park et al., 2021), it is apparent that CFC‐11 emissions have additional sources such as chlorofluorocarbon banks (Lickley et al., 2020, 2021). Furthermore, these emissions are also subject to stratospheric dynamical influences, particularly modulation by the QBO (Ray et al., 2020; Ruiz et al., 2021).…”