Synergistic effects of CO2 and air pollutants from ship emissions in Shanghai, China: Spatial-temporal characteristics, prediction assessment, policy implications.

Currently, the goal of achieving net-zero emissions for ships presents a significant challenge to CO2 reduction policies. A comprehensive analysis of ship air pollutants and CO2 emissions is crucial for mitigating greenhouse effect and air pollution. To realize the overall control policies of ship emissions, this study established a high-resolution emissions inventory for air pollutants (CO, HC, NOx, PM2.5, PM10, SO2) and CO2 from 11 types of ships in Shanghai, and conducted analyses of spatiotemporal characteristics, spatial heterogeneity and consistency, and synergistic effects. Results indicated significant monthly and weekly variability in ship emissions. Due to the varying contribution rates of large ocean-going vessels, the temporal-spatial distributions of CO, HC, NOx, and CO2 revealed significant differences compared to PM2.5, PM10, and SO2. CO2 had a positive synergy in emissions with CO, HC, NOx according to the spatial heterogeneity and consistency analysis. Phasing out of old ships and implementing carbon capture technology were more conducive to CO2 reduction, while the replacement of clean energy contributed greater potential in reducing air pollutant emissions. Comprehensive mitigation measures hold effective co-benefits in air pollutants and CO2 reductions, with the synergistic effect index approaching 1. The implementation of strengthened control measures would minimize the ship emissions, achieving a 78.1% reduction in CO2, and have a positive long-term effect on co-control emission reduction. This study combines high-precision analysis, prediction assessment, and synergistic effects, providing a reference for the development of refined ship management policies in megacities worldwide.