To improve air quality and to reduce its harmful impact on human health, a better knowledge of particle sources, particularly in areas submitted to recurrent pollution episodes as observed in northern France, is needed. For this purpose, developing methodologies of identification and localization of these sources, based on the chemical characterization of particles, is important. Using statistical analysis of the chemical composition of PM10 at several sites for at least one year and a half, the objectives of this work are: - to identify the nature and geographical origin of sources impacting the north of France, distinguishing between background pollution and local inputs; - to better understand exceedance episodes by determining the main sources contributing to these events and their geographical origin. Integrated in the CARA program (Chemical Characterization of Particles), created and maintained by the LCSQA (Laboratoire Central de Surveillance de la Qualité de l'Air), sampling of PM10 particles has been performed at five different sites (3 urban background, 1 traffic, 1 remote) by four regional monitoring networks.