A source apportionment methodology has been implemented to estimate the contribution from different arid geographical areas to the levels of measured atmospheric particulate matter with diameters less than 10 ¿m (PM10). Toward that end, the Hybrid Single-Particle Lagrangian Integrated Trajectory model (HYSPLIT) has been used to quantify the proportions of mineral dust originated from specific geographical areas in northern Africa. HYSPLIT simulates the transport, dispersion, and deposition of dust plumes as they travel from the source areas to the receptors. This model has been configured to reproduce high daily ambient PM10 levels recorded at three Spanish EMEP (Cooperative Programme for Monitoring and Evaluation of the Long-Range Transmission of Air pollutants in Europe) regional background monitoring stations, located over the central Iberian Peninsula, during a North African dust outbreak from 12 to 15 March 2003. Different model setups have been utilized to determine the best suite of parameters needed to better represent the observed concentrations. Once the simulation has been configured, the model has been run for individual scenarios which include eight specific source areas over northern Africa considered as possible contributors to the PM10 levels measured at the monitoring stations. One additional run has been carried out to account for the rest of the dust sources in northern Africa. Furthermore, the fractional contribution to the PM10 air concentrations at the receptors from each run has been used to estimate the source apportionment. According to these calculations, the contribution from each area to the PM10 recorded over central Iberia for the March 2003 episode can be detailed as follows: 20--30% of the PM10 dust originated in Mauritania and the western Sahara, 15--20% from Mali, Mauritania and the western flanks of the Ahaggar Mountains, and 55--60% from other northwestern African sources within the rest of the desert source area.