Describe the key factors that determine where a gas and a pa

Describe the key factors that determine where a gas and a particle react or become deposited in the pulmonary system.

Solution

The key factors that determine where a gas and a particle react or become deposited in the respiratory tract are:

1. The size of the particle: for sperical particles the size is given by particle diameter (dp). In the case of irregularly-shaped particles, an equivalent diameter can be used and is defined by the diameter of a sphere of equal volume. The size of respirable particles range from a few nanometers to few microns.

The transport behavior of an aerosol particle depends on its interaction with the surrounding gas molecules. This interaction can be characterized by considering

When Kn » 1 (i.e., » dp) the behavior of the particle and surrounding gas requires the kinetic theory of gases.

On the other hand, when Kn « 1, (i.e. « dp), the probability that surrounding gas molecules strike the particle surface is high, and the surrounding gas affects the behavior of the particles through a drag force.

2. The shape of the particle: Since the shape of the particle contributes to its diffusive and aerodynamic nature, this plays a kep factor in the deposition in the repsiartory tract.

3. Density of the particle: While desnity remains same as that of the original material.., many particles of conglomerate to form a mass of bulk density. This in turn affects the rate of deposition.

4. Chemical Properties (Nucleation, Condensation, Hygroscopicity): These play significant roles. The vapour pressure of a liquid droplet and the realtive humidity associated with the inetraction between the nose and the inhales gas play a role in deposition in the rspiratory tract. Hygroscopicity is imporatnt as few partucles might increase in size and density by absorbing water molecules as they move upward the respiratory tract. This might affect the intensity of deposition.

5. Diffusion coefficient of the particles: The effect of movement of small molecules under brownian movement and the effect of larger molecules of larger particles under the force of gravity tend to affect their diffusional co-efficient. This is turn affects the deposition in the respiaratory tract.