<p>Most population-aggregated cities in developing countries are facing severe air pollution due to high concentrations of PM_2.5 and O₃, which could be associated with the impacts of local mesoscale circulations. The river land breeze (RLB) and mountain valley breeze (MVB) circulations made PM_2.5 and O₃ pollution causes more complicated in inland regions. By combining monitoring and simulating data from the inland region, this study analyzed the influence of local mesoscale circulations on pollutant concentrations and their underlying mechanisms. The daily average and peak concentrations of pollutants in RLB days and MVB days were different from those in non-RLB days and non-MVB days, indicating that local mesoscale circulations exerted distinct influences on regional pollutant concentrations. Moreover, hourly PM_2.5 concentrations had a notable reduction during winter in RLB days when compared to non-RLB days (1.6–18.7 μg/m³), meanwhile, they increased the most during spring (1.3–7.0 μg/m³) and decreased the most during winter (2.5–14.3 μg/m³) in MVB days when compared to non-MVB days. Hourly O₃ concentrations increased the least during winter in RLB days compared to non-RLB days (6.6–22.4 μg/m³), meanwhile, they showed the largest increase during spring (32.3 μg/m³) and the smallest increase during winter in MVB days compared to non-MVB days (13.2 μg/m³). Both the RLB and MVB could disperse particulate horizontally through the lower branches, with the extent of dispersion varying according to wind speeds in different seasons. The recirculation dominated by stronger branches (river/valley breezes) could enhance the formation of both O₃ and secondary PM_2.5 by prolonging the residence time within the region and promoting the pollutant mixing. Based on those diverse contributions, targeted management strategies will be highly desirable in regions over riverine and mountainous terrains in the inland region in Yichang, China, and similar cities around the world.</p> Graphical Abstract <p></p>