The dispersion of ozone (O3) and other reactive pollutants in a street canyon with a canyon aspect ratio (H/W, where H is the canyon height and W is the canyon width) of two is investigated using a computational fluid dynamics (CFD) model coupled with a photochemistry model. The CFD model is a Reynolds-averaged Navier-Stokes equations (RANS) model with the renormalization group (RNG) k-e turbulence closure model, and the photochemistry model includes the carbon bond IV mechanism with 36 gaseous species. The emission source of NOx and VOCs is located at the bottom of the street canyon, and five different ambient wind speeds are considered. Two vortices, a clockwise-rotating upper vortex and a counterclockwise-rotating lower vortex, are formed in the street canyon. A chemically active region appears near the mid-height of the downwind building wall where an upward flow associated with the lower vortex and a downward flow associated with the upper vortex are faced with each other. While O3 is transported from the overlying atmosphere into the street canyon, the net O3 production averaged over the lower part of the street canyon is negative because of the pronounced NO titration of O3. In contrast, the net O3 production averaged over the upper part of the street canyon is positive because of the pronounced NO2 photolysis. As the ambient wind speed increases, the micromixing between the two parts of the street canyon as well as the inflow across the roof level contributes to the increasing O3 concentration tendencies due to the advection and turbulent diffusion, concurrent with the decreasing net O3 production. The chemical O3 production or loss rate is well correlated with some photochemical aging indicators such as NO2/NO, NOy/NOx, and VOC ratios. Accordingly, the micromixing effects on the O3 concentration in the street canyon are clearly explained using the indicators in terms of photochemistry, which can be applied to neighborhood scale or larger scale chemistry.