The aviation industry's rapid expansion, particularly on China-foreign routes, significantly contributes to climate change. While much research focuses on CO2 emissions, aircraft also release other pollutants like CO, HC, NOx, SO2, and PM2.5, each with detrimental environmental and health consequences. Existing emission calculation methods, such as the ICAO method, EPA method, and EMEP method, have limitations in accurately accounting for all pollutants across different flight stages and aircraft types. This paper addresses these gaps by employing a Modified BFFM2-FOA-FPM method to calculate the total emissions of six pollutants from China-foreign routes. The study also utilizes the Global Warming Potential (GWP) concept, incorporated within the Aviation FAIR-GWP concentration method, to account for the varying climate impacts of different pollutants, expressed as carbon dioxide equivalent (CO2-e). The Aviation FAIR-GWP concentration method considers environmental absorption of greenhouse gases, a factor often neglected in traditional GWP calculations. This comprehensive approach allows for a more accurate assessment of the overall climate impact of aviation emissions on China-foreign routes. The study further analyzes the role of ETS and SAFs, both individually and in combination, to determine the most effective pathway for emission reduction in this rapidly growing sector. This detailed analysis on China-foreign routes, one of the world’s fastest-growing aviation markets, offers valuable insights for developing effective emission reduction strategies globally.

Numerous studies have focused on calculating CO2 emissions from aircraft, highlighting their significant contribution to the greenhouse effect. However, less attention has been paid to the other pollutants emitted by aircraft, including CO, HC, NOx, SO2, and PM2.5. Existing methods for calculating non-CO2 emissions, such as the ICAO method (BFFM2 and FOA), the American EPA method, and the European EMEP method, have limitations in accurately accounting for all pollutants across different flight stages and aircraft types. Previous research on climate effects of greenhouse gases, starting in the 1970s, initially focused on ozone depletion potential (ODP) and halocarbon global warming potential (HGWP). Later, the accumulated greenhouse effect (AG(x)) and the Absolute Global Warming Potential (AGWP) were introduced to encompass a broader range of greenhouse gases, allowing for conversion into CO2-e equivalents. The most widely used metric, the Global Warming Potential (GWP), integrates radiative forcing over a specified time horizon. While GWP100 is now a standard metric for expressing emissions in both scientific and public discourse, it often overlooks environmental absorption processes. Existing research on aviation emission reduction strategies has mostly focused on either ETS or SAFs in isolation, lacking a systematic comparison and analysis across specific regions and pollutants. This study fills this gap by comprehensively analyzing both approaches, considering various sub-scenarios and specific emission data for China-foreign routes.

This study utilizes a two-pronged approach: First, a modified BFFM2-FOA-FPM method is employed to calculate actual emissions of six pollutants (CO2, CO, HC, NOx, SO2, PM2.5) for China-foreign routes from 2014 to 2021. Data on flight information, including aircraft type, flight frequency, distance, and time, were sourced from VariFlight.com, supplemented by engine data from the ICAO Aircraft Engine Emissions Databank. Second, a novel Aviation FAIR-GWP concentration method is developed to calculate CDEC, incorporating the environmental absorption of greenhouse gases and accounting for the varying climate impacts of different pollutants. This method builds upon the FAIR model (versions 1.0 and 1.3) which tracks the time integral fraction of carbon in the atmosphere and considers carbon sink efficiencies. Equations (1)-(3) are used to calculate CO2 concentration, while equations (5) and (6) calculate CH4 and N2O concentrations. Equation (7) calculates CDEC by summing CO2, CH4, and N2O concentrations, weighted by their respective global warming potentials. The study sets four scenarios: a baseline scenario (average emissions from 2014-2021), a scenario with only ETS (based on CNG2020 strategy, considering various sub-scenarios depending on whether carbon neutrality is achieved by 2035 or 2040), a scenario with only SAFs (considering varying SAF mix proportions over time), and a combined scenario with both ETS and SAFs. The study then compares the resulting CDEC across different scenarios to assess the effectiveness of each emission reduction approach.

The analysis reveals that under the baseline scenario, CO2 emissions show a significant upward trend until 2019, followed by a decline due to the COVID-19 pandemic. However, a continued increase in CO2 and CDEC is projected until 2100. Implementing ETS alone, based on the CNG2020 strategy, results in significant reductions in CO2 concentration, but the overall impact on CDEC is limited because other pollutants are not addressed. If carbon neutrality is achieved by 2035, CO2 and CDEC reductions are approximately 18%, while achieving neutrality by 2040 results in around 35% reduction. Introducing SAFs alone leads to substantial decreases in CO2, CH4, and N2O concentrations. Implementing 50% SAFs by 2025 and 100% by 2030 leads to the most significant reductions compared to the baseline scenario (66.94% for CO2 and considerably lower for CH4 and N2O). However, the combined implementation of both ETS and SAFs proves the most effective. In scenarios where carbon neutrality is achieved by 2035 and a high proportion of SAFs is used (50% by 2025 and 100% by 2030), CO2 and CDEC reductions reach approximately 85%, with substantial reductions in CH4 and N2O.

The findings underscore the importance of considering both ETS and SAFs for effective aviation emission reduction. While ETS primarily tackles CO2, SAFs offer a more comprehensive solution by addressing multiple pollutants simultaneously. The study’s results on China-foreign routes demonstrate that a combined strategy surpasses the effectiveness of either approach individually. The significant reductions in CDEC achieved under the combined approach highlight its potential for mitigating the overall climate impact of aviation. This systematic comparison provides crucial evidence for policymakers in developing comprehensive aviation emission reduction strategies. The success of the CNG2020 strategy in reducing CO2 emissions is notable, but its limitations regarding non-CO2 pollutants are apparent. This underscores the need for a more holistic approach that incorporates both ETS and SAFs to address the full spectrum of aviation emissions.

This paper offers a systematic comparison of ETS and SAFs for reducing aircraft emissions on China-foreign routes. The key finding is that the combined application of both approaches is significantly more effective in decreasing CDEC than either strategy alone, especially when considering achieving carbon neutrality by 2035. This emphasizes the importance of multi-faceted strategies in mitigating aviation's environmental impact. Future research should explore the economic aspects of implementing these strategies, considering factors such as SAF production costs, ETS carbon pricing, and potential uncertainties in future emission projections.

This study has certain limitations. It does not account for the changing costs of aircraft transformation and maintenance associated with SAF use, the fluctuating price of carbon credits, or the varying costs of SAFs produced from different sources. The analysis does not account for the different emission reduction potentials of SAFs produced from various feedstocks and using different production technologies. The study also does not explicitly model uncertainties related to future emission scenarios, technological advancements, or economic factors that may influence the effectiveness of ETS and SAFs in the long term. These limitations suggest avenues for future research to refine these models and gain a more nuanced understanding of the pathways for reducing aviation emissions.