Air quality is a main environmental concern of the Macau Special Administrative Region (SAR) citizens. The region is highly affected by particulate matter (PM) pollution, which anthropogenic sources are road and maritime transport as well as domestic, industries and construction activities. Moreover, Macau SAR is affected by the external influence of air pollution from its neighbouring regions. Notwithstanding the potential use of air quality modelling to provide scientific advice on atmospheric emission reduction strategies, air quality forecast, air pollution assessment and air quality regulations at several spatial scales, there are only few air quality modelling applications over the Macau SAR area. This study aims to design A muLti-scaLe aIr pollutioN mOdelliNg systEm (ALL-IN-ONE) to provide scientific advice to policy makers in their strategic planning to improve the air quality and to assess the PM pollution phenomena over Macau SAR. The ALL- IN-ONE is based on the selection of a set of models able to reproduce the meteorological and air quality patterns, from regional to the local scales. The system revealed a good performance for meteorological and air quality modelling simulations and it tends to underestimate the PM concentrations. From the application of the ALL-IN-ONE, it was possible to identify a main contribution of neighbouring regions which caused exposure of Macau SAR population to high PM levels. Some PM pollution mitigation measures were designed and tested, with a reduction of concentration levels, but still with several daily PM exceedances estimated over the study area. It is necessary to join efforts with neighbouring regions to discuss/apply air pollution reduction measures in order to improve the air quality over the Macau SAR. The results of this work demonstrate the importance of modelling tools (ranging from regional to local scales) to study air pollution phenomena over Macau SAR and to define efficient air quality management strategies.