Projected increases in emissions of high global warming potential fluorinated gases in China

The study focuses on high-GWP fluorinated greenhouse gases (F-GHGs)—sulfur hexafluoride (SF6), nitrogen trifluoride (NF3), and four perfluorocarbons (CF4, C2F6, C3F8, c-C4F8)—which are long-lived and potent climate forcers. Unlike CH4 and N2O, these species (except CF4) are predominantly anthropogenic. While hydrofluorocarbons (HFCs) have been examined extensively elsewhere, comprehensive, up-to-date information on China’s historical and projected emissions of SF6, NF3, and PFCs is limited due to incomplete species coverage, missing sectors, and sparse reporting years, especially as China, a UNFCCC non-Annex I Party, does not submit annual inventories. Given China’s commitment to peak CO₂ by 2030 and reach carbon neutrality by 2060 (with ambiguity over non-CO₂ gases), the research aims to construct a thorough bottom-up inventory for 1990–2019 covering all major F-GHGs and sectors, validate with top-down constraints, quantify China’s contribution to global totals, and project 2020–2060 emissions to assess implications for national climate targets and global radiative forcing and temperature.

Prior official Chinese inventories to UNFCCC reported only select F-GHGs (typically SF6, CF4, C2F6) and limited years (2005, 2010, 2012, 2014). Earlier bottom-up studies often missed species and sectors (e.g., Fang et al. covered only SF6; EDGAR versions included fewer sectors), and the US EPA database lacked the most recent years for China. Top-down studies using atmospheric observations and inversions provided estimates for limited periods (e.g., NF3 for 2014–2015; CF4 2008–2015; C2F6 and C3F8 for 2008; c-C4F8 2010–2017), constraining understanding of long-term trends. HFC emissions in China are relatively well characterized in earlier work and are excluded here; other fluorinated species (SO2F2, less abundant PFCs, anesthetic gases) lack activity data and contribute minimally to totals. This study addresses gaps by including six key F-GHGs, comprehensive sector coverage, and continuous annual estimates since 1990, with validation against available top-down results.

Bottom-up annual emissions of SF6, NF3, CF4, C2F6, C3F8, and c-C4F8 were estimated for 1990–2019 across 13 source sectors in mainland China: (1) F-GHGs production, (2) electrical equipment, (3) magnesium production, (4) primary aluminum production, (5) semiconductor manufacture, (6) flat panel display screens manufacture, (7) photovoltaics manufacture, (8) medical use, (9) gas-air tracer experiments, (10) fire extinguishing use, (11) military use, (12) refrigeration use, and (13) HCFC-22 feedstock use. Activity data (production, consumption = production + imports − exports, and disposal) were compiled from yearbooks, reports, industry sources, and expert interviews. Emission estimation followed decision trees and factors from IPCC 2006 Guidelines and 2019 Refinement, Fang et al., and other literature. Example formulations include: E = EF × P for production-related fugitive releases, and for electrical equipment SF6: E(t) = EFmanufact/install × C(t) + EFleak × B(t) + EFmaint/disposal × B(t) × (1 − R), where C is annual consumption, B is bank, EF are emission factors for manufacturing/installation, leakage, and maintenance/disposal, and R is recovery. GWP values over 100-year time horizon from IPCC AR4 were used for CO2-equivalent calculations to align with UNFCCC reporting. Uncertainty was quantified via Monte Carlo simulation (1,000,000 iterations) varying activity data and emission factors assuming normal distributions; uncertainties were sourced from literature and IPCC, with 50% assigned where unavailable. Projections (2020–2060) were derived by establishing linear relationships (correlation 0.86–1.00) between historical GDP and sectoral F-GHG production/consumption over recent years and applying future GDP trajectories from ten SSP-based scenarios (IIASA and OECD Env-Growth, SSP1–SSP5). Sectoral emissions were then projected using the same emission calculation framework. Radiative forcing and temperature impacts were computed from projected emissions using lifetimes, molecular weights, radiative efficiencies, and a climate sensitivity parameter (λ = 0.8 °C W−1 m2), following Velders et al., to estimate atmospheric mole fractions, radiative forcing, and incremental temperature changes relative to 2019.

- Historical growth: Total F-GHG emissions in China rose from 5.5 to 221 Mt CO2-eq yr−1 between 1990 and 2019. - Species contributions (2019): SF6 115 ± 31 Mt CO2-eq (52%), CF4 48 ± 18 Mt (21%), NF3 29 ± 12 Mt (13%), c-C4F8 14 ± 9.7 Mt (6.1%), C2F6 13 ± 4.8 Mt (5.7%), C3F8 3.6 ± 2.2 Mt (1.6%). - Sector contributions (2019): Electrical equipment 24%, semiconductor manufacture 22.1%, primary aluminum 13%, medical use 7.4%, HCFC-22 feedstock use 5.7%. - Drivers of 1990–2019 increase: By species—SF6 52.7%, CF4 20.3%, NF3 13.5%, remaining three gases together 13.5%. By sector—electrical equipment 24.2%, semiconductor manufacture 22.7%, primary aluminum 11.7%, medical use 7.6%, HCFC-22 feedstock 5.8%, others 27.9%. - Global contributions: China’s share of global emissions increased to 55% (SF6), 70% (NF3), 47% (CF4), 49% (C2F6), 72% (C3F8), and 58% (c-C4F8) by 2019. China’s total F-GHG emissions surpassed Annex I totals in 2007 and were ~8× Annex I totals by 2019. In 2018, China’s F-GHG total (198 Mt CO2-eq) exceeded that of all other non-Annex I countries combined (177 Mt CO2-eq). From 2000–2019, the global increase was 160 Mt CO2-eq, with China’s increase 201 Mt, Annex I decrease 57 Mt, and other non-Annex I increase 16 Mt—China accounted for ~93% of the global increase. - Projections: Under no additional mitigation (BAU), China’s F-GHG emissions are projected to reach 506–1356 Mt CO2-eq yr−1 by 2060, comparable to or exceeding projected national CO2 emissions under carbon neutrality scenarios (600–1090 Mt yr−1 in 2060). - Climate impact: Projected additional global radiative forcing due to China’s F-GHGs by 2060 is 16.5–32.2 mW m−2, corresponding to a temperature increase of 0.013–0.025 °C. - Validation: Bottom-up estimates show good agreement with top-down studies for overlapping periods, e.g., SF6 2007–2012 and CF4/C2F6 in recent years.

By constructing a comprehensive, sector- and species-resolved inventory for 1990–2019 and validating against atmospheric inversions, the study addresses the lack of detailed information on China’s F-GHG emissions. Results show China has become the dominant global source for these high-GWP gases, driven by growth in electrical equipment, semiconductor manufacturing, and primary aluminum sectors, and limited mitigation to date. The prioritization for control emerges clearly: SF6 contributes the largest share to warming, followed by CF4 and NF3, with major emitting sectors identified for targeted interventions. Projections indicate that without explicit regulation, F-GHG emissions could offset anticipated CO2 reductions under carbon neutrality if non-CO2 gases are excluded, adding measurable radiative forcing and temperature increase. These findings underscore the importance of incorporating F-GHG controls into China’s climate strategy and international efforts, and of implementing sector-specific mitigation (e.g., leak reduction, alternative gases, abatement technologies) to curb future warming impacts.

The study delivers the most comprehensive bottom-up inventory to date of China’s SF6, NF3, and key PFC emissions across 13 sectors for 1990–2019, validated with top-down estimates, and quantifies China’s increasing dominance in global F-GHG emissions and contributions to radiative forcing. Projections under BAU indicate 2060 emissions of 506–1356 Mt CO2-eq yr−1, potentially equaling or exceeding projected CO2 emissions under carbon neutrality if non-CO2 gases are not included. Main contributions include full species and sector coverage, alignment with UNFCCC-compatible GWPs, and quantified climate implications. Future work should prioritize: expanding and updating activity data and emission factors, especially for emerging sectors; implementing and evaluating mitigation technologies and alternative gases; integrating F-GHGs explicitly into national neutrality targets; and enhancing observation networks and inverse modeling to continuously validate inventories.

- Species coverage: HFCs, SO2F2, less abundant PFCs (e.g., C4F10, C5F12, C6F14), and fluorinated anesthetics were excluded due to lack of activity data; their omission is assessed to have minor effect on totals but still introduces underestimation. - Data gaps: Non-Annex I reporting and limited industrial transparency lead to uncertainties in activity data and emission factors for some sectors and years. - Top-down constraints: Atmospheric observations are limited prior to ~2008, restricting validation of early-year estimates. - Method assumptions: Use of IPCC AR4 GWPs (to align with reporting) affects CO2-eq magnitudes relative to other GWP versions; sectoral emission factors and recovery rates may vary geographically and over time. - Projections: Future emissions are based on linear relationships with GDP and SSP scenarios; structural changes, technology shifts, policy interventions, and mitigation adoption could alter trajectories substantially.