Trifluoromethane (CHF3, HFC-23) is one of the most potent greenhouse gases (GHGs), and eastern China has been recognized as a major source region, yet highly inconsistent emission estimates warrant more extensive studies. In this study, we conducted 2-year online measurements of halocarbons during 2021-2023 at an urban site in the Pearl River Delta region. The observed average HFC-23 mixing ratios of 43.6 +/- 7.8 ppt were similar to 20% enhanced compared to observations at the Mace Head global baseline station. Unlike other halocarbons with significant local emissions, HFC-23 mixing ratios showed distinct seasonal variations with peak values in winter and bottom values in summer. Similar seasonal patterns and highly significant correlation were observed between HFC-23 and perfluorocyclobutane (c-C4F8, PFC-318), a co-product from manufacturing PTFE using chlorodifluoromethane (CHClF2, HCFC-22) as feedstock. The weighted potential source contribution function analysis also demonstrated eastern China was the major source area for both HFC-23 and PFC-318. Tracer-based estimation revealed HFC-23 emissions of 6.7 +/- 3.1 Gg yr-1 (equivalent to 98 Tg-CO2 yr-1 or 0.7% China's annual GHG emissions in 2021) in eastern China. Our results highlight the importance of HFC-23 emission control in eastern China for China's GHG and F-gases emission reductions, and suggest that greater attention should be given to HFC-23 emissions from PTFE production, which is emerging as a more substantial source than previously anticipated. Trifluoromethane, also known as HFC-23, is a very strong greenhouse gas produced unintentionally during the manufacturing of chlorodifluoromethane (HCFC-22). It is among target fluorine-containing greenhouse gases whose emissions should be controlled under the Kigali Amendment. While a lot of HFC-23 is believed to come from eastern China, it is hard to say exactly how much. From 2021 to 2023, we measured HFC-23 and other fluorinated gases in air at an urban site in the Pearl River Delta region. We found HFC-23 levels were about 20% higher than that at global background sites. We noticed that HFC-23 and another gas called perfluorocyclobutane (PFC-318), which is a co-product when manufacturing PTFE with HCFC-22, were strongly linked and both had seasonal patterns quite different from other fluorinated gases. Our analysis shows that PFC-318 and HFC-23 mostly come from eastern China. By using PFC-318 as a tracer, we estimated the amount of HFC-23 emissions in eastern China at 6.7 +/- 3.1 Gg yr-1, making up a small but important part of China's overall greenhouse emissions. This highlights the need to lower HFC-23 emissions, particularly those from the process of making PTFE with HCFC-22. HFC-23 mixing ratios measured online during 2021-2023 were 43.6 +/- 7.8 ppt, similar to 20% higher than that at the Mace Head baseline station HFC-23 emissions mainly occurred in eastern China with estimated emissions of 6.7 +/- 3.1 Gg yr-1 during 2021-2023 Feedstock use of HCFC-22 for producing PTFE is emerging as an increasingly significant emission source of HFC-23
