The air that we inhale are laden with dust, smoke, droplets and many other suspended particles. These get deposited in the airways and pose a risk to our health—be it disease-causing pathogen carrying droplets or harmful toxic aerosols. To understand their effect, the study of airflow, particle transport and deposition in the lung is of significance. We present a detailed computational fluid and particle dynamics (CFPD) study of airway bifurcations present in the human lung. In particular, we focus on the different physical phenomena leading to particle deposition. We find that gravitational sedimentation is the primary mode by which particles with higher Stokes number deposit on the bronchial walls. In addition, we show the manner in which efficiency of deposition is influenced by the orientation of the airway with respect to gravity.