This study focuses on the effect of the morphology and the pore structure of two different porous substrates, namely wood-wool cement board (WWCB) and autoclaved aerated concrete (AAC), on the air pollutant removal efficiency by photocatalytic oxidation (PCO). Their rough surface and porous structure make them appealing choices for nitric oxide (NO) de-pollution, under indoor conditions. In-depth material characterization of the two substrates is realized in order to understand the effect of the porosity, roughness and surface area on the PCO efficiency, at different air flow rates. PCO assessment shows that both activated substrates can degrade up to 99% of NO. The morphology and pore structure analyses of the two substrates reveal that a high effective area and roughness increases the PCO efficiency and an open pore structure allows a better air flow, avoiding NO2 release.