Question

A bag filter is used for removal of particulate matter having a range of sizes. The correct sequence of air filtration mechanisms for their removal, in order of decreasing size, is

• A. Diffusion, Impaction, Disintegration
• B. Disintegration, Impaction, Interception
• C. Diffusion, Impaction, Interception
• D. Impaction, Interception, Diffusion

Hint:

Remember: large particles crash (impaction), medium ones touch (interception), tiny ones wander (diffusion).

Answer 1

The Correct Option is A

Step 1: Understand filtration mechanisms by particle size.
Impaction removes large particles (coarse PM) because they cannot follow air streamlines and impact directly onto filter fibers. 
Interception removes medium-size particles that follow streamlines but touch fibers and get captured. 
Diffusion removes the smallest particles (PM$_{2.5}$, ultrafine) due to Brownian motion. 
Step 2: Arrange from largest to smallest particle size. 
Largest particles → Impaction 
Medium particles → Interception 
Smallest particles → Diffusion 
Thus the correct decreasing size sequence is: \[ \boxed{\text{Impaction} ;>; \text{Interception} ;>; \text{Diffusion}} \] This corresponds to option (D). 
Final Answer: (D)