Toward resolving the mysterious budget discrepancy of ozone-depleting CCl 4 : An analysis of top-down emissions from China

Abstract. Emissive production and use of carbon tetrachloride (CCl 4 ), one of the first-generation ozone-depleting substances, have been banned by the Montreal Protocol with the 2010 phase-out for developing countries, but production and consumption for non-dispersive use as a chemical feedstock and as process agent are still allowed. Here, we present evidence that significant unreported emissions of CCl 4 still persist, based on the high frequency and magnitude of CCl 4 pollution events observed in the 8-year real time atmospheric measurement record at Gosan station, a regional background monitoring site in East Asia. From this we estimate top-down emissions of CCl 4 amounting to 23.6 ± 7.1 Gg yr −1 from 2011 to 2015 for China, in contrast to the 4.3–5.2 Gg yr −1 reported as the most up-to-date post-2010 Chinese bottom-up emissions. The missing emissions (~ 19 Gg yr −1 ) for China are highly significant, contributing about 54 % of global CCl 4 emissions. We show that 89 ± 6 % of the CCl 4 enhancements observed at Gosan can be accounted for by fugitive emissions of CCl 4 occurring at the factory level during the production of CH 3 Cl, CH 2 Cl 2 , CHCl 3 and C 2 Cl 4 (PCE) and feedstock and solvent use in chemical manufacturing industries. Thus, it is crucial to implement technical improvements and better regulation strategies to reduce the evaporative losses of CCl 4 occurring at the factory and/or process level.