We investigate a micro cavity plasma array (MCPA) reactor operated at atmospheric pressure, offering excellent diagnostic accessibility and flexible opportunities for catalyst integration. Here, the dissociation of CO2 diluted in helium into CO is investigated. The diagnostic setup, combining TALIF with an ICCD camera, enables three-dimensional spatially resolved measurements of CO number densities below the CO-generating discharges. The measured distributions are compared to a basic three-dimensional diffusion model, showing good agreement and revealing the dominant transport mechanisms. Flow variation studies indicate that the gas flow inside the reactor follows a laminar, Poiseuille-like profile, while the transport behavior is consistent with literature values for the diffusion coefficient of CO, further validating the model. The high estimated local dissociation within the MCPA discharges (about 40%) results in saturation of CO fraction under increasing voltage. Combined with complementary diagnostics already presented for this discharge, including measurements of surface charges, electric fields, and atomic oxygen, this approach provides a suitable platform for systematic studies of plasma–catalyst interactions.