Top-down Estimates of HFC-134a and HCFC-142b Emissions in East Asia in 2022 and 2023 Using a Bayesian Inversion Framework

Long‑lived halocarbons have been subject to progressive international regulation due to their significant impacts on stratospheric ozone depletion and climate forcing. Following the phase‑out of chlorofluorocarbons (CFCs) under the Montreal Protocol, hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) were introduced as transitional and long‑term substitutes. While HCFCs are being phased out globally, legacy emissions still persist, and HFCs, despite their zero ozone‑depletion potential, have become a growing concern because of their high global warming potentials, prompting further controls under the Kigali Amendment.

Within this regulatory and scientific context, emissions of HFCs and HCFCs in East Asia have attracted substantial attention over the past decades. This region hosts some of the world’s most intensive production, consumption, and use of fluorinated refrigerants, with southeastern China in particular representing a major hotspot of anthropogenic activity. Previous studies have identified the Pearl River Delta (PRD) and Yangtze River Delta (YRD) as key source regions for multiple halocarbon species, making East Asia a focal area for evaluating emission trends, inventory accuracy, and policy effectiveness.

The Hong Kong University of Science and Technology (UST) atmospheric observatory plays a key role in monitoring halocarbon mole fractions across East Asia. Owing to its coastal location and favorable meteorological conditions, the site is sensitive to air masses originating from a broad swath of the region, including the highly developed areas of southeastern China such as the PRD and YRD. Leveraging continuous observations from the UST site together with background measurements, we applied a FLEXPART‑based Bayesian inversion framework to quantify emissions of HFC‑134a and HCFC‑142b over East Asia. This approach provides regional‑scale emission constraints that are directly relevant for assessing long‑lived halocarbon emissions under current control policies.