## 4 Results and Discussion
### Prediction Using ML Regression  
The ML prediction model calculated the DE of the right lung and left lung for the 17-generation model. The DE was calculated for a wide range of flow rates and particle sizes, which was unavailable from the CFD measurement. The overall DE was calculated for the left and right lung and the five different lobes for the large-scale model. The schematic in Figure 5 shows the areas for the different parts of the 17-generation model. Figure 4: GPI values for different ML regression models. Figure 5: Definition of the local regions of the 17-generation airway model: (**a**) left and right lung, and (**b**) five different lobes. original pathline, they touch the airway wall and become trapped on the highly viscous surface of the airway wall. However, aerosols can follow the air streamline at low flow inlet conditions, minimising the overall DE at the upper airways. The right lung anatomical diameter is higher than the left lung, and the right lung consists of three airway lobes while the left contains two lobes. The complex anatomical shape and branching structure, higher flow distribution to the right lung, flow rates and particle inertia influence the overall DE at the right lung. The DE for the right and the left lung increased with the flow rates, which closely aligns with the CFD data, and it also satisfies the general aerosol deposition hypothesis in airways. Figure 6b-f show a similar trend of DE for different diameter particles. Figure 6d-f show the DE for 7 \(\upmu\)m, 8.5 \(\upmu\)m and 10 \(\upmu\)m diameter particles, which is significantly higher than the smaller particles. Larger diameter particles mean the particle inertia will be higher, and the impaction mechanism is dominant for larger particles. At high flow condition, the inertial impaction became more dominant for the larger diameter particles and influenced the overall DE. Figure 6: _Cont._  
The comparison of DE in different lobes with respect to flow rate and particle diameter for particle sizes of 2.5 \(\upmu\)m and 7.5 \(\upmu\)m is shown in Figure 7. For a 2.5 \(\upmu\)m diameter particle, the DE is higher at the right lower lobe and lower at the left upper lobe irrespective of the deposition parameter. It is also noticed that the DE of 2.5 \(\upmu\)m particles at the right lower lobe increased with the flow rate. The overall DE at the right and left upper lobes is lower than the right and left lower lobes. The upper lobes' branches are in the upward direction and opposite to the gravitational force, while the lower lobes are in the downward direction. Micron-sized particles mostly travel downward due to the high inertia, which transports fewer aerosols to the upper lobes of the airways, and less deposition occurs at the upper lobes. Figure 7b shows the 7.5 \(\upmu\)m aerosol DE at different lobes, and a similar trend is observed at various lobes. At the flow rate (15 L/min), DE at the left upper lobe is different from other lobes. The overall DE at the left upper lobe is higher for low flow rate and lower for high flow rate. At a high flow rate, larger diameter particles deviate from the streamline and transport to the lower airways, while at a low flow rate, more particles transport to the upper airways. The overall DE at the right middle lobe shows a similar trend for 2.5 \(\upmu\)m and 7.5 \(\upmu\)m particles. Figure 6: Predicted DE for different flow rates: (**a**) 1 \(\upmu\)m particle, (**b**) 2.5 \(\upmu\)m particle, (**c**) 5 \(\upmu\)m particle, (**d**) 7 \(\upmu\)m particle, (**e**) 8.5 \(\upmu\)m particle and (**f**) 10 \(\upmu\)m particle. Figure 7: Comparison particle DE in the different lobes of the left and right lungs for flow rates of (**a**) 2.5 \(\upmu\)m and (**b**) 7.5 \(\upmu\)m.  
A comprehensive lobe-specific DE was calculated for various diameter particles. Figure 8 shows the DE at different lobes of the 17-generation model for 15 L/min, 30 L/min and 60 L/min flow rates. The general trend shows higher DE at the lower lobes of the left and the right lung for all cases.