Deposition of particles in different regions of the lung depends on particle size and density. Particle size ranges from 1 nm to 100 μm, particle density tested: 0.1 g/cm3 (left panel), 1.0 g/cm3 (centre panel) and 10.0 g/cm3 (right panel) (Simulation made in Multiple Pathway Particle Dosimetry Model V2.1 Copyright ARA 2009, based on human oronasal-normal augmenter breathing). The figure shows the deposition of inhaled particles in the extra-thoracic region (black line), the tracheobronchial region (grey line), and the alveolar region (red line). In the alveolar region, the deposition is the highest for nanoparticles with a primary or agglomerate particle size between 10 nm and 100 nm, regardless of the density. For particles with a primary or agglomerate size between 100 nm and 1 μm, the (agglomerate) density influences the deposition in the lungs: in this size range particles/agglomerates with a higher density will deposit more efficiently in the alveolar region compared to particles/agglomerates with a lower density.