Emissions of Ozone-Layer-Depleting Methyl Chloroform (CH3CCl3) in China Inferred from High-Frequency In-Situ Observations

Abstract

Methyl chloroform (CH₃CCl₃, TCA), a first-generation ozone-depleting substance leading to ozone depletion, is regulated under the Montreal Protocol. However, recent atmospheric observations and emission estimates for TCA in China are lacking, leaving the effectiveness of the Montreal Protocol’s implementation unclear. In this study, we collected 2727 atmospheric samples at the Shanghuang site in eastern China from August 2023 to July 2024. Using these observations with a Bayesian inversion algorithm, we quantify emissions of TCA in eastern China during August 2023–July 2024 at 0.21 ± 0.04 gigagram per year (Gg yr^–1), comprising about 10.2% of global emissions. Moreover, TCA emissions in whole China have declined from 6.0–10.5 Gg yr^–1 in 2003 to 0.30 ± 0.06 Gg yr^–1 during August 2023–July 2024, demonstrating effective phase-out under the Montreal Protocol. Nonzero emissions likely arise from fugitive emissions in industrial processes (e.g., iron and steel industry, refined petroleum industry, and coking industry) and nonindustrial sources (e.g., biomass combustion), which are not controlled by the Protocol. Continued monitoring of TCA mole fractions and emissions would be valuable for confirming the sustained success of China’s phase-out efforts and long-term compliance.