This study aims to develop a multi-scale atmospheric emission inventory for the transport sector with high spatial and temporal resolution using Portugal as a case study. For that, a combination of the traditional method of emissions calculation with an innovative way to gather and process data (BigAir approach) was implemented. The accuracy of the developed inventory was evaluated by applying a multi-scale air pollution system, with two sets of data: i) BigAir and ii) EMEP emission inventories. The scalability and replicability nature of the BigAir approach allows it to be used by the scientific community in other regions of the world.