Persistent emissions of ozone-depleting carbon tetrachloride from China during 2011-2021

Lingering global emissions of carbon tetrachloride (CCl4) are slowing ozone layer recovery. Estimates of global CCl4 emissions based on observed atmospheric mole fractions and inverse modelling (top-down) exceed the emissions derived from known sources (bottom-up) by ~30-40%. Here, we derived CCl4 emissions from China for 2011-2021 using long-term atmospheric observations from a network of sites from across China and a top-down approach. Mean annual CCl4 emissions in China during 2011-2021 were between approximately 16 and 25 Gg yr-1, and are substantially larger than previous bottom-up inventories for China of less than 6 Gg yr-1 since 2011. Expressed in terms of CFC-11-eq emissions, CCl4 annual emissions from China are comparable to global annual “unexpected” CFC-11 emissions during 2013-2018, or global total annual HCFC emissions in 2020. The CCl4 emissions from China accounted for approximately half of the reported global total during 2011-2020, with neither showing a significant decreasing trend during this period. Substantial CCl4 emissions in China from allowed feedstock use, during the renewed production of
CFC-11 between 2013-2018, and from by-production could close some of the emissions gap. Yet, ~4-15 Gg yr-1 of CCl4 emissions in China remain unexplained during 2011-2021, potentially accounting for more than half of the remaining global gap.