The study of particulate pollution is an issue that receives ever increasing attention globally. The European Union has established strict limits on the permissible levels of concentration of suspended particles as a whole (as well as for some of their constituents), with which Member States must otherwise face the risk of imposing severe fines on them. The study of the levels of suspended particles in the atmosphere provides information on the health risk of residents and is important for identifying the problem. It does not, however, provide much evidence of the causes, which need to be known in order to be able to deal with it. The most effective way of addressing this problem is to identify the sources of the suspended particles as well as to quantify the contribution of each of them, thus enabling targeted response. Since in Greece it is known that background concentrations of suspended particles may be too high, in order to properly assess the actual impact of local sources, this background should be assessed first. The aim of the proposed project is to identify the sources of particulate matter PM1 (i.e. with a diameter of less than 1 micrometer) in peripheral and urban background areas in the region of Western Greece. The determination will be done for the first time using two different methods that provide additional information.