Marine cloud brightening (MCB) has been proposed as a regional solar radiation modification strategy, yet its effects on atmospheric composition remain poorly understood. Here, using the Community Earth System Model version 1 (CESM1), we isolate the climate-mediated response of surface ozone (O₃) with a three-stage experimental design. We first determine a sea salt injection rate of 11.4 Tg yr^−1 in each of six oceanic regions, which is sufficient to offset the 1.0 W m^−2 effective radiative forcing difference between SSP5-8.5 and SSP2-4.5 in 2050. We then simulate the coupled climate response and prescribe the resulting sea surface temperature and sea ice fields in atmospheric chemistry experiments without additional sea salt injection. The MCB injection decreases global annual mean sea surface temperature by 0.44 °C and increases Arctic sea ice concentration by 9.7 %. The resulting changes in temperature, moisture, radiation, boundary-layer mixing, and transport produce spatially heterogeneous surface O₃ responses. After a machine learning bias correction, boreal summer surface O₃ concentration decreases by 0.33 μg m^−3 over China, remains nearly unchanged over Europe at +0.01 μg m^−3, and increases by 0.12 μg m^−3 over the United States. The subregional responses are more pronounced with decreases of 0.59 and 0.64 μg m^−3 over western and eastern China and contrasting changes of −0.19 and +0.14 μg m^−3 over western and eastern Europe. A comprehensive evaluation of MCB should therefore consider its consequences for regional air quality alongside its intended climate effects.