1 6 A D V A N C E D M A T E R I A L S & P R O C E S S E S | M A R C H 2 0 2 3 optically thinner contrails, and less global warming due to aviation. Hydrogen combustion yields zero sulfate and non-volatile particulate emissions, but 2.6 times more water vapor. Increased humidity in the exhaust combinedwith the presence of airborne aerosols may increase the probability of occurrence of contrails. However, the absence of sulfates and non-volatile particulates may decrease the radiative forcing of persistent contrails and aviation induced contrail cirrus clouds. Additional research is needed to quantify the impact of alternative fuel sulfur content, aromatic hydrocarbon concentration, carbon-to-hydrogen ratio, and airborne aerosol concentration on the contrail formation process and associated radiative forcing effects. This re- search learning would be used to assess the overall environmental impact of suite of sustainable propulsion technologies and alternative fuels as well as influence the technological and operational strategies for detecting, avoiding, and mitigating contrails and their environmental effects. SUMMARY Climate change impacts people and economies. As a result, mitigating the impacts of anthropogenic climate change to meet the goals of the United Nations Paris Agreement signed in 2016 is one of the most urgent challenges of our time. The shared goal of the Paris Agreement was to limit global warming to 1.5°C above pre-industrial levels. The aviation industry, which accounts for approximately 2.5% of global CO2 emissions, could potentially contribute a greater share of global CO2 emissions by 2050 due to the estimated increase in customer demand for air travel. Pratt & Whitney has affirmed the ATAG agreement to help achieve net zero air transport carbon emissions by 2050. The International Air Transport Association(IATA) approvedaresolution for the global aviation industry to achieve net zero CO2 emissions by 2050. Pratt & Whitney’s approach consists of developing technologies, such as high efficiency, low-emissions aircraft engines compatible with cleaner fuels, such as ASTM-approved, drop-in compatible sustainable aviation fuels and green hydrogen. Non-CO2 emissions effects, including contrail effects, further increase the aviation industry’s overall environmental impact. Specifically, contrail effects may rival that of CO2 as contributors to global warming due to commercial aviation traffic, yet there is significant uncertainty in these assessments. Further study is required to fully understand the impact of alternate fuels on the contrail formation process and effective radiative forcing of contrail cirrus clouds. The learning from these contrail studies would provide the aviation industry with valuable data to fully evaluate the impact of proposed sustainable propulsion technologies and alternative fuels on the environment. ~AM&P Note Pratt & Whitney GTF and Pratt & Whitney GTF Advantage are trademarks of Pratt & Whitney. Formore information: Sean Bradshaw, senior fellow, sustainable propulsion, Pratt & Whitney, 400 Main St., East Hartford, CT 06118, 860.294.6392, sean.bradshaw@prattwhitney.com. References 1. Waypoint 2050. ATAG. https:// aviationbenefits.org/media/167417/ w2050_v2021_27sept_full.pdf. 2. Net Zero Carbon Emissions by 2050, IATA, October 4, 2021. 3. Aviationbenefits.Org, https://aviationbenefits.org/media/166152/beginners-guide-to-saf_web.pdf. 4. Total fuel consumption of commercial airlines worldwide between 2005 and 2019, IATA / ICAO, https://www. statista.com/statistics/655057/fue l-consumption-of-airlines-worldwide/. 5. M.D. Staples, et al., Aviation CO2 Emissions Reductions from the Use of Alternative Jet Fuels, Energy Policy, Vol. 114, p 342-354, 2018. 6. Commercial Alternative Aviation Fuels Initiative (CAAFI), https://www. caafi.org/focus_areas/fuel_qualification.html. 7. FAA Response to Research, Engineering, and Development Advis- ory Committee Recommendations for the Fiscal Year 2023 Research and Development Portfolio, https:// www.faa.gov/about/office_org/head- quarters_offices/ang/redac/media/responses/RecommendationsResponse- FY2023.pdf. 8. Sustainable Aviation Fuel: Review of Technical Pathways, Office of Energy Efficiency & Renewable Energy, U.S. Department of Energy, p 9-10, September 9, 2020, https://www.energy.gov/eere/bioenergy/downloads/ sustainable-aviation-fuel-review-technical-pathways-report. 9. D.S. Lee, et al., The Contribution of Global Aviation to Anthropogenic Climate Forcing for 2000 to 2018, Atmospheric Environment, Vol. 244, 117834, January 2021. 10. Cleaner Burning Aviation Fuels Can Reduce Contrail Cloudiness, Article number: 114 (2021), Communications Earth & Environment, https://www.nature.com/articles/s43247-021-00174-y. 11. STEP-Tech Demonstrator, Pratt & Whitney Press Release, December 20, 2022, https://newsroom.prattwhitney. com/2022-12-20-Raytheon-TechnologiesCompletes-First-Engine-Run-of-RegionalHybrid-Electric-Flight-Demonstrator. 12. SWITCH, Pratt & Whitney Press Release, November 29, 2022, https:// newsroom.prattwhitney.com/2022-1129-Clean-Aviation-SWITCH-Project-toAdvance-Hybrid-Electric-and-WaterEnhanced-Turbofan-Technologies.
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