Constraining the carbon tetrachloride (CCl 4 ) budget using its global trend and inter‐hemispheric gradient

Carbon tetrachloride (CCl 4 ) is a major anthropogenic ozone‐depleting substance and greenhouse gas and has been regulated under the Montreal Protocol. However, the near‐zero 2007–2012 emissions estimate based on the UNEP reported production and feedstock usage cannot be reconciled with the observed slow decline of atmospheric concentrations and the inter‐hemispheric gradient (IHG) for CCl 4 . Our 3‐D model simulations suggest that the observed IHG (1.5 ± 0.2 ppt for 2000–2012) is primarily caused by ongoing current emissions, while ocean and soil losses and stratosphere‐troposphere exchange together contribute a small negative gradient (~0 – −0.3 ppt). Using the observed CCl 4 global trend and IHG, we deduce that the mean global emissions for the 2000–2012 period are 39 34 45  Gg/yr (~30% of the peak 1980s emissions) and a corresponding total lifetime of 35 37 32  years.