The development of an improved theoretical model for predicting particle deposition during inhalation requires accurate knowledge of respiratory system geometry, air flow structure inside the airways related to the breathing patterns and physical properties of aerosol particles defined through their shape, morphology, geometric dimension and density. For most aerosols, the main particle deposition mechanisms are inertial impaction, sedimentation, interception and Brownian diffusion. The particles considered in this paper, both environmental and therapeutic, have a complex structure due to the process they are produced through. Generally such particles are nano-structured and consist of many spherical primary nanoparticles with diameters of the order of 10 nm. The main mechanisms of deposition of these particles within the respiratory system are Brownian diffusion and interception. In the present paper we will analyze some deposition models of diffusional particles at the characteristic part of human airways.