The atmospheric concentrations and emissions of major halocarbons in China during 2009-2019

Atmospheric observation and emission estimation of HFC-125 and HFC-32 in China from four representative cities

HFC-125 and HFC-32 are fluorinated greenhouse gases of great concern due to their high GWPs and increasing background atmospheric concentrations. Long-term atmospheric observations of HFC-125 and HFC-32 were carried out in four representative cities of China (Beijing, Guangzhou, Hangzhou, and Lanzhou) from January 2012 to October 2019. Overall, the annual mean atmospheric concentrations of HFC-125 and HFC-32 both showed increasing trends, with average rates of 4.8 ppt yr-1 and 7.9 ppt yr-1. The average concentrations of HFC-125 and HFC-32 in urban areas were significantly higher than those in suburban areas. Significant differences in atmospheric concentrations of the two HFCs were observed among the four cities. HFC-125 and HFC-32 emissions were estimated accordingly, averaging 6.2 Gg yr-1 (23.6 Mt. CO2-eq) and 5.7 Gg yr-1 (4.3 Mt. CO2-eq) during 2012 and 2019 and growing at rates of 0.8 Gg yr-1 (3.1 Mt. CO2-eq) and 0.8 Gg yr-1 (0.6 Mt. CO2-eq), respectively, with an increasing contribution to global radiative forcing. The bottom-up inventories of HFC-125 and HFC-32 in the four cities increased annually from 2012 to 2019, with the highest emissions in Beijing, while the top-down emissions fluctuated during the research period. SYNOPSIS: The atmospheric concentrations of HFC-125 and HFC-32 were measured from 2012 to 2019 in four representative cities of China. Both HFC emissions at national and city levels were estimated using observation-based and inventory methods.

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.

Boosting Catalytic and Anti-fluorination Performance of the Ru/Vanadia-Titania Catalyst for the Oxidative Destruction of Freon by Sulfuric Acid Modification

Chlorofluorocarbons (CFCs) exert a strong greenhouse effect and constitute the largest contributor to ozone depletion. Catalytic removal is considered an effective pathway for eliminating low-concentration CFCs under mild conditions. The key issue is the easy deactivation of the catalysts due to their surface fluorination. We herein report a comparative investigation on catalytic dichlorodifluoromethane (CFC-12) removal in the absence or presence of water over the sulfuric-acid-modified three-dimensionally ordered macroporous vanadia-titania-supported Ru (S-Ru/3DOM VTO) catalysts. The S-Ru/3DOM VTO catalyst exhibited high activity (T90% = 278 °C at space velocity = 40 000 mL g-1 h-1) and good stability within 60 h of on-stream reaction in the presence of 1800 ppm of water due to the improvements in acid site amount and redox ability that promoted the adsorption of CFC-12 and the activation of C-F bonds. Compared with the case under dry conditions, catalytic performance for CFC-12 removal was better over the S-Ru/3DOM VTO catalyst in the presence of water. Water introduction mitigated surface fluorination by the replenishment of hydroxyl groups, inhibited the formation of halogenated byproducts via the surface fluorine species cleaning effect, and promoted the reaction pathway of COX2 (X = Cl/F) → carboxylic acid → CO2.

Inverse Modeling Revealed Reversed Trends in HCFC-141b Emissions for China during 2018-2020

Having the highest ozone-depleting potential among hydrochlorofluorocarbons (HCFCs), the production and consumption of HCFC-141b (1,1-dichloro-1-fluoroethane, CH3CCl2F) are controlled by the Montreal Protocol. A renewed rise in global HCFC-141b emissions was found during 2017-2020; however, the latest changes in emissions across China are unclear for this period. This study used the FLEXible PARTicle dispersion model and the Bayesian framework to quantify HCFC-141b emissions based on atmospheric measurements from more sites across China than those used in previous studies. Results show that the estimated HCFC-141b emissions during 2018-2020 were on average 19.4 (17.3-21.6) Gg year-1, which was 3.9 (0.9-7.0) Gg year-1 higher than those in 2017 (15.5 [13.4-17.6] Gg year-1), showing a renewed rise. The proportion of global emissions that could not be exactly traced in 2020 was reduced from about 70% reported in previous studies to 46% herein. This study reconciled the global emission rise of 3.0 ± 1.2 Gg year-1 (emissions in 2020 - emissions in 2017): China's HCFC-141b emissions changed by 4.3 ± 4.5 Gg year-1, and the combined emissions from North Korea, South Korea, western Japan, Australia, northwestern Europe, and the United States changed by -2.2 ± 2.6 Gg year-1, while those from other countries/regions changed by 0.9 ± 5.3 Gg year-1.

Projections of National-Gridded Emissions of Hydrofluoroolefins (HFOs) in China

Hydrofluoroolefins (HFOs) are being used as substitutes for potent greenhouse gas hydrofluorocarbons (HFCs). However, the use and environmental impacts of HFOs are of great concern due to the rapid degradation of HFOs to produce persistent and phytotoxic trifluoroacetic acid (TFA). Here, we provide a comprehensive projection of HFO emissions in China during 2024-2060 for the first time. Under the Kigali Amendment to the Montreal Protocol, China's HFO emissions are estimated to increase from 1.7 (1.3-2.3) to 148.8 (111.4-185.4) kt in 2024-2060 with cumulative emissions of 2.8 (2.0-3.5) Gt, and cumulative reduced HFCs emissions are evaluated to be 5.4 Gt CO2-equivalent. High HFO emissions would be distributed mainly in the North China Plain and the eastern and coastal areas. HFO-1234yf (2,3,3,3-tetrafluoropropene) contributes most of HFO emissions with a cumulative emission of 1.7 Gt in 2024-2060, while the cumulative increment of TFA deposition from HFO-1234yf emissions would reach 0.4-1.0 Gt. The long-term national-gridded HFO emission inventories can provide scientific support for evaluating the environmental risks of HFOs and developing HFC phase-out pathways for addressing climate change.

In Situ Observations of Halogenated Gases at the Shangdianzi Background Station and Emission Estimates for Northern China

Halogenated gases include ozone-depleting substances and greenhouse gases, such as chlorofluorocarbons, halons, hydrochlorofluorocarbons, hydrofluorocarbons, and perfluorinated gases. In situ atmospheric observations of major halogenated gases were conducted at the Shangdianzi (SDZ) background station, China, from October 2020 to September 2021 using ODS5-pro, a newly developed measurement system. The measurement time series of 36 halogenated gases showed occasional pollution events, where background conditions represented 25% (CH₂Cl₂) to 81% (CF₃Cl, CFC-13) of the measurements. The annual mean background mole fractions of most species at SDZ were consistent with those obtained at the Mace Head station in Ireland. The background conditions were distinguished from pollution events, and the enhanced mole fractions were used to estimate the emissions of four categories of fluorinated gases (F-gases) from northern China using a tracer ratio method. The CO₂-equivalent (CO₂-equiv) emission of F-gases from northern China reached 181 ± 18 Tg year^-1 during 2020-2021. Among the four categories of F-gases estimated, SF₆ accounted for the highest proportion of CO₂-equiv emissions (24%), followed by HFC-23 (22%), HFC-125 (17%), HFC-134a (13%), NF₃ (10%), CF₄ (5.9%), HFC-143a (3.9%), HFC-32 (3.4%), and HFC-152a (0.2%).

Banks, emissions, and environmental impacts of China's ozone depletion substances and hydrofluorocarbon substitutes during 1980-2020

Ozone-depleting substances (ODSs), which also contribute to global warming, have been controlled by the Montreal Protocol (MP) since 1987. China joined the MP in 1991 and began reducing production and consumption of ODSs in the country, leading to a decrease in emissions of ODSs. Based on the Intergovernmental Panel on Climate Change guidelines, the latest emission factors and actual consumption in China (MP scenario), both the historical banks and the historical emissions of ODSs and substitute hydrofluorocarbons (HFCs) during 1980-2020 were calculated. To understand the reduction in ODS and HFC emissions by implementing the MP, we also estimated China's virtual emissions (NMP, i.e., the amount of ODS emissions without the MP) over the same period. The avoided cumulative ODS consumption and emission values of 10.8 and 5.8 (4.8-6.9) million tonnes (Mt) of CFC-11-equivalent (eq), respectively, were estimated by comparing the two scenarios. Furthermore, 26 (22-33) giga tonnes (Gt) of CO₂-eq emissions, equivalent to an increase of 0.031 W m^-2 radiative forcing, were estimated to be avoided by 2020, which will prevent an additional 0.025 °C increase in temperature. The MP implemented by China has resulted in substantial environmental benefits over the last 30 years. However, owing to the massive use of HFCs as substitutes, the cumulative emissions reached 2286 Mt. CO₂-eq during 1990-2020, and it will be challenging to phase down HFCs in the environment after China ratified the Kigali Amendment in 2021.

Atmospheric Observation and Emission of HFC-134a in China and Its Four Cities

1,1,1,2-Tetrafluoroethane (HFC-134a) is widely used as a refrigerant to replace dichlorodifluoromethane (CFC-12), and a small amount of it is used in the foam and medical aerosol sectors, with a high global warming potential and fast-increasing atmospheric concentration. The emission of HFC-134a in China has been growing at an average annual growth rate of 14.4% since 2009, reaching 53.0 (47.5-58.7) kt yr^-1 in 2020. Among the five emission sources, emissions from the mobile air conditioning (MAC) sector accounted for the highest proportion of 65% on average of the total, followed by the commercial air conditioning (CAC) sector (25%), the medical aerosols sector (8%), the foam sector (2%), and leakage emission from the production (less than 0.1%). The emissions of HFC-134a in four cities in China (Beijing, Guangzhou, Hangzhou, and Lanzhou) were also estimated and discussed. Beijing had the highest HFC-134a emission of 2.2 kt yr^-1 in 2020, and Lanzhou had the lowest emission of only 0.2 kt yr^-1. In Beijing and Guangzhou, emissions from the CAC sector surpassed those from the MAC sector, becoming the most important source of HFC-134a. The average annual growth rate of HFC-134a's emissions during 2009-2019 was close to its concentration enhancement growth rate of 12.7%, and the emissions also showed significant correlations with the concentration enhancements in both China and four cities. This indicates the importance of the muti-city and long-term observations for the verification of HFC-134a's emission estimates at a regional scale.

Characteristics and source apportionment of some halocarbons in Hangzhou, eastern China during 2021

In recent years, eastern China has been identified as an important contributor to national and global emissions of halocarbons, some of which are ozone depletion substances (ODSs) that delay the recovery of the stratospheric ozone layer. However, the most recent characteristics and sources of halocarbons in eastern China remain unclear. Thus, hourly atmospheric observations of halocarbons were conducted in Hangzhou throughout 2021. The results showed that methylene chloride (CH₂Cl₂) was the most abundant halocarbon (2207 (25 %-75 % quantile: 1116-2848) ppt; parts per trillion) followed by chloromethane (CH₃Cl) (912 (683-1043) ppt), and 1,2-dichloroethane (CH₂ClCH₂Cl) (596 (292-763) ppt). Then, backward trajectory and potential source contribution function (PSCF) analysis show that the emission hot spots of halocarbons were concentrated in adjacent cities in Zhejiang and neighboring provinces in eastern China. Moreover, based on positive matrix factorization (PMF) analysis, industrial emission (38.7 %), solvent usage (32.6 %), and the refrigeration sector and biomass burning (23.7 %) were the main sources of halocarbons (observed in this study). This study reveals high concentrations and potential sources of halocarbons in eastern China, which are important for studying the recovery of the ozone layer.

Anthropogenic emissions of ozone-depleting substance CH3Cl during 2000-2020 in China

Methyl Chloride (CH₃Cl) is the largest source of stratospheric chlorine, which has a significant impact on the depletion of the stratospheric ozone layer. Detailed information on anthropogenic CH₃Cl emissions in China is still lacking. This study establishes a comprehensive bottom-up inventory of anthropogenic CH₃Cl emissions in China during 2000-2020. Results show that China's anthropogenic CH₃Cl emissions have increased significantly, from 34.1 ± 11.6 Gg/yr (gigagrams per year) in 2000 to 128.5 ± 26.5 Gg/yr in 2018 with a slight decrease to 124.9 ± 26.0 Gg/yr in 2020. The main sources of anthropogenic emissions of CH₃Cl in China are chemical production (37.1%), solvent use (35.4%), and coal combustion (13.6%) in 2020. China's contribution to global anthropogenic emissions of CH₃Cl reached almost 50%. Moreover, the ratios of CH₃Cl CFC-11-eq emissions relative to emissions of ozone-depleting substances (ODSs) controlled under the Montreal Protocol in China have increased from 0.8% in 2000 to 11.6% in 2020 and are estimated to continue increasing in the future. In summary, China's anthropogenic CH₃Cl emissions have shown an increasing trend in the past two decades, made a huge contribution to the total global anthropogenic emissions, and presented a potential increasing impact on the depletion of the ozone layer and global warming.

On-line trace monitoring of volatile halogenated compounds in air by improved thermal desorption-gas chromatography-mass spectrometry

Volatile halogenated compounds (VHCs) are important industrial chemicals and play a crucial role in potential stratospheric ozone-depletion and global warming. Profiling of VHCs is of great significance but replete with challenges due to the species' richness and diversity. In this study, we developed a novel method employing water removal mode combined with thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS) for on-line measurement of VHCs at the ultratrace level. By removing water with Nafion dryer tandem cold trap device, VHCs could achieve better separation and identification, and detection precision of VHCs lower than 10%. The proposed method exhibited limits of detection for VHCs ranging from 0.1 to 6.2 pptv. Benefiting from the improved trapping efficiency due to water removal, we successfully quantified 34 VHCs at the Shangdianzi background station and achieved a comprehensive assessment of VHCs in ambient air.

Estimate of hydrochlorofluorocarbon emissions during 2011-2018 in the Yangtze River Delta, China

Hydrochlorofluorocarbons (HCFCs) are used as temporary substitutes for chlorofluorocarbons and other ozone-depleting substances because they have reduced ozone depletion and global warming potentials. The consumption and production of HCFCs are regulated via the Montreal Protocol and its amendments till 2013, with a complete phase-out being scheduled by 2030 for Article 5 parties (developing countries). To better understand the characteristics and emissions of HCFCs in the Yangtze River Delta (YRD), which is the largest metropolitan area in China, weekly flask samples were collected at the Lin'an regional background station located in the YRD from 2011 to 2018 and measured for four HCFCs (HCFC-22, HCFC-141b, HCFC-142b, and HCFC-124). The HCFC-132b and HCFC-133a measurements began in 2018. The ambient mixing ratios of the HCFCs exhibited higher concentrations and larger variabilities than those at the Shangri-la regional background station at similar latitudes in southwest China. The HCFC emissions in the YRD were estimated based on the tracer ratio method using CO and HFC-134a as tracers, and were comparable within the uncertainties. Our results are generally consistent with previous estimates obtained using top-down approaches. HCFC-22 and HCFC-141b contributed 52% ± 23% and 41% ± 24% of the total ODP-weighted (CFC-11-equivalent) HCFC emissions from the YRD, respectively, whereas HCFC-22 contributed the most (83% ± 36%) to the total CO₂-equivalent HCFC emissions from the YRD. The cumulative ODP-weighted and CO₂-equivalent emissions of HCFCs from the YRD accounted for 25% ± 15% and 20% ± 11% of the national corresponding totals, respectively, for 2011-2017. The HCFC-141b emissions from the YRD contributed approximately half of the total Chinese emissions. HCFC-133a emissions in the YRD accounted for approximately one-fifth of the global total in 2018. Thus, the YRD is an important contributor of HCFC emissions on national and global scales.

Atmospheric volatile halogenated hydrocarbons in air pollution episodes in an urban area of Beijing: Characterization, health risk assessment and sources apportionment

Volatile halogenated hydrocarbons (VHCs) have attracted wide attention in the atmospheric chemistry field since they not only affect the ecological environment but also damage human health. In order to better understand the characteristics, sources and health risks of VHCs in typical urban areas in Beijing, and also verify the achievement in implementing the Montreal Protocol (MP) in Beijing, observational studies on 22 atmospheric VHCs species were conducted during six air pollution episodes from December 2016 to May 2017. The range in daily mixing ratios of the 6 MP-regulated VHCs was 1000-1168 pptv, and the 16 MP-unregulated VHCs was 452-2961 pptv. The 16 MP-unregulated VHCs accounted for a relatively high concentration proportion among the 22 VHCs with a mean of 70.25%. Compared with other regions, the mixing ratios of MP-regulated VHCs were in the middle concentrations. The mixing ratios of the MP-regulated VHCs remained the same concentrations during the air pollution episodes, while the concentrations of MP-unregulated VHCs were generally higher on polluted days than on clean days and increased with the aggravation of the pollution episodes. The mixing ratios of dichlorodifluoromethane and trichlorofluoromethane were higher than Northern Hemisphere (NH) background values, while the mixing ratios of the other 4 MP-regulated VHCs were moderate and similar to the NH background values. All the 9 VHCs with carcinogenic risk might pose potential carcinogenic risks to the exposed populations in the six pollution episodes, while none of the 12 VHCs might pose appreciable non-carcinogenic risks to the exposed populations. Considering the higher concentration levels and higher risk values of 1,2-dichloropropane, 1,2-dichloroethane, carbon tetrachloride and trichloromethane, Beijing needs to further strengthen the control of these VHCs. The analysis of air mass transportation and PMF model showed that regional transportation and leakage of CFCs banks were important sources of VHCs in Beijing, and the contribution of industrial process and solvent usage should not be neglected. The results revealed the effective implementation of the MP in Beijing and its surrounding areas, while further measures are suggested to control the emissions of important VHCs especially from regional transportation and leakage of CFCs banks to reduce the possible health risks to the exposed population.