Question

Column I presents common air pollutants, and column II presents treatment technologies commonly employed to control air pollutants.

	Air pollutant		Treatment technology
1	Dust (size 5-25 microns)	P	Cyclone separator
2	Carbon monoxide (CO)	Q	Wet lime-water scrubber
3	Sulfur dioxide (SO2)	R	Electrostatic precipitator
4	Fly ash (size < 2.5 microns)	S	Catalytic converter

The option that CORRECTLY matches the air pollutant with its treatment technology is:

• A. 1 - P ; 2 - S ; 3 - Q ; 4 - R
• B. 1 - P ; 2 - R ; 3 - S ; 4 - Q
• C. 1 - R ; 2 - Q ; 3 - P ; 4 - S
• D. 1 - R ; 2 - Q ; 3 - S ; 4 - P

Hint:

Match by pollutant type: coarse dust to cyclone, fine fly ash to ESP, acid gas SO2 to wet scrubbing, CO gas to catalytic oxidation.

Answer 1

The Correct Option is A

Air pollution control equipment is chosen based on two things: whether the pollutant is a solid particle or a gas, and if it is a particle, how fine it is. Let's sort the four pollutants on that basis.

1. 1. Dust (5-25 microns): This is a coarse particulate. A cyclone separator, which spins the gas stream so heavier particles are thrown out by centrifugal force, is good at removing particles in this size range cheaply, so it pairs with P, Cyclone separator.
2. 2. Carbon monoxide (CO): CO is a gas, not a particle, so it cannot be removed by any particulate collector at all, cyclone, ESP or otherwise. It has to be destroyed chemically, and a catalytic converter oxidizes CO to CO₂ over a catalyst bed. So it pairs with S, Catalytic converter.
3. 3. Sulfur dioxide (SO₂): SO₂ is also a gas, an acid gas, and the standard way to remove acid gases from a flue stream is to absorb them in an alkaline liquid, commonly a lime or lime-water slurry, in a wet scrubber. So it pairs with Q, Wet lime-water scrubber.
4. 4. Fly ash (below 2.5 microns): This is a very fine particulate, too fine for a cyclone to catch efficiently. An electrostatic precipitator charges the fine particles and pulls them onto collector plates, giving very high efficiency even at sub-micron sizes. So it pairs with R, Electrostatic precipitator.

Putting these together: 1-P, 2-S, 3-Q, 4-R. Checking the given options, this exact combination is option (A). Any option that assigns a gas (CO or SO₂) to a particulate-only device like the cyclone or ESP, or assigns the very fine fly ash to a coarse-particle cyclone, must be wrong.

Let's summarize:

• Coarse dust: cyclone separator.
• CO gas: catalytic converter, chemical oxidation.
• SO₂ acid gas: wet lime-water scrubber, absorption.
• Very fine fly ash: electrostatic precipitator.

So the correct match is option (A).