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

Abstract

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 Gg yr⁻¹ and 25 Gg yr⁻¹, substantially larger than previous bottom-up inventories for China of less than 6 Gg yr⁻¹ since 2011. Expressed in terms of ozone depletion potential (ODP)-weighted emissions, CCl₄ annual emissions from China are comparable to global annual ‘unexpected’ trichlorofluoromethane (CFC-11) emissions during 2013–2018, or global total annual hydrochlorofluorocarbon 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 and 2018, and from by-production could close some of the emissions gap. However, ~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.