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Passenger transportation significantly contributes to urban carbon dioxide emission. Decreasing these emissions is essential to achieving low-carbon development. This research focused on Xi'an City to enhance previous research works by considering factors such as road greening, online ride-hailing, and use of vehicles with new energy sources. Using system dynamics method, a carbon dioxide emission prediction model was developed for urban passenger transportation in Xi'an. The developed model estimated total emissions from 2012 to 2021 and projected carbon dioxide emission reduction plans through six different scenarios for the time period of 2023 to 2032. The analysis identified private cars as the main contributors to carbon emission in urban passenger transportation. Single scenario simulations indicated that passenger traffic in Xi'an would not achieve carbon emission peak by 2030, but multi-scenario simulations showed it would. Specific recommendations for carbon emission reduction in urban passenger transportation were provided, focusing on travel patterns, energy sources, and promotion of green initiatives. [ABSTRACT FROM AUTHOR]

The performance of UV/H2O2, UV/O3 and UV/H2O2/O3 oxidation systems for treating spent caustic from an ethylene plant was investigated. In UV/H2O2 system, with the increase of H2O2 dosage, removal efficiencies of COD and the ratio of biochemical oxygen demand (BOD) to chemical oxygen demand (COD) of the effluent were increased and a better performance was obtained than the H2O2 system alone. In UV/H2O2 system, removal efficiency of COD reach 68% under the optimum condition, and BOD/COD ratio was significantly increased from 0.22 to 0.52. In UV/O3 system, with the increase of O3 dosage, removal efficiency of COD and BOD/COD ratio were increased, and a better performance was obtained than the O3 system alone. Under the optimum condition, removal efficiency of COD was 54%, and BOD/COD ratio was significantly increased from 0.22 to 0.48. In UV/H2O2/O3 system, COD removal efficiency was found to be 22.0% higher than UV/O3 system.