Emissions of HCFC-22 and HCFC-142b in China during 2018-2021 Inferred from Inverse Modeling

Hydrochlorofluorocarbons (HCFCs) are transitional substitutes for chlorofluorocarbons (CFCs). However, they still have the capacity to be ozone-depleting substances (ODSs). Therefore, they are scheduled to be phased out in China by 2030 under the Montreal Protocol. The emission estimates of HCFC-22 (CHClF₂) and HCFC-142b (CH₃CClF₂) in China using atmospheric observations are lacking after 2017, making it hard to understand the effectiveness of the phase-out process of HCFCs in China. Here, we use flask and in situ measurements of HCFC-22 and HCFC-142b during 2018-2021 and inverse modeling to determine the emission magnitude and changes in China. It was determined that China's emissions were 172 ± 40, 154 ± 39, 160 ± 22, and 155 ± 33 Gg yr^-1 of HCFC-22 and 8.3 ± 1.8, 7.8 ± 1.6, 7.4 ± 1.7, and 7.9 ± 1.7 Gg yr^-1 of HCFC-142b from 2018 to 2021, respectively. Top-down estimates show that HCFC-22 emissions in China were stable, while HCFC-142b emissions were decreasing during 2013-2021, although both substances were in the stage of being phased out during 2013-2021. This study reveals that 46 and 39% of the global HCFC-22 and HCFC-142b emissions, respectively, cannot be traced to certain countries in 2020. We suggest that more studies on HCFC emissions around the world in the future are needed to better safeguard the ozone layer recovery and climate mitigation by ensuring compliance with the Montreal Protocol during HCFC phase-out processes.