Shipping emissions are a major source of nitrogen oxides (NO_x) in coastal regions and play an increasingly important role in regional atmospheric oxidation and ozone (O₃) formation. Using a high-resolution WRF–CMAQ modeling framework, we quantify the impacts of shipping emissions on NO₂, O₃, and total oxidants (Ox = O₃ + NO₂) over the Yangtze River Delta (YRD), China, during 2021. We further investigate the response of regional air quality to abrupt changes in shipping activities during the 2022 Shanghai epidemic lockdown and evaluate future emission-control strategies under 2030 scenarios. Shipping emissions increase NO₂ concentrations by more than 40 μg m^-3 in coastal waters and substantially modify regional oxidation capacity. O₃ responses exhibit strong spatial heterogeneity, with increases of 8–16 μg m⁻³ in NO_x-limited regions but decreases in VOC-limited coastal and urban areas due to NO titration. The 2022 Shanghai lockdown provides a natural experiment to isolate the effects of shipping emission changes. Despite reduced shipping emissions in Shanghai, local O₃ increased by approximately 25%, whereas neighboring port regions experienced O₃ decreases because of the spatial redistribution of maritime traffic. Future scenario analyses further show that transportation-oriented NO_x reductions alone could increase coastal O₃ by 8–16 μg m⁻³, while coordinated reductions of NO_x and VOCs decrease O_x by 10–20% during spring and summer. These results highlight the importance of nonlinear atmospheric chemistry and demonstrate that effective ozone mitigation in coastal megacity regions requires coordinated, multi-sector emission control strategies rather than isolated reductions from individual sectors.