Indoor Air Pollution & Control

You’ll be able to

Identify the major indoor air pollutants in developed and developing nations
Describe technologies that reduce pollutant emissions from combustion sources
Calculate the mass of pollutant removed by a control device of given efficiency

Indoor air pollutants

Indoor air is often more polluted than outdoor air. In developed nations, key indoor pollutants include radon — a naturally occurring radioactive gas that seeps from soil and rock into basements and is a leading cause of lung cancer; asbestos — a fibrous insulation material that causes lung disease when its fibers are inhaled; carbon monoxide from faulty heaters and stoves; VOCs and formaldehyde off-gassing from paints, furniture, and carpets; and tobacco smoke. In developing nations, the dominant hazard is particulate matter and CO from burning wood, charcoal, or dung indoors for cooking and heating without ventilation.

Sick building syndrome and mitigation

When many occupants of a modern, tightly sealed building report headaches, fatigue, and irritation that ease when they leave, the cause is often sick building syndrome — a buildup of indoor pollutants (VOCs, molds, CO₂) in a structure with poor ventilation. Because energy-efficient buildings are sealed against air leaks, they can also trap pollutants. Remedies are straightforward: improve ventilation, test for and vent radon, remove or seal asbestos, use low-VOC materials, and maintain combustion appliances.

Controlling pollution at the source

Several technologies cut pollutant emissions from combustion. Scrubbers spray a wet slurry (often limestone) through smokestack gas to remove SO₂ before it exits. Electrostatic precipitators charge particulates so they stick to collector plates, removing most particulate matter from flue gas. Catalytic converters on vehicles convert CO, NOₓ, and unburned hydrocarbons into less harmful CO₂, N₂, and water. Baghouse filters trap particles in fabric bags. These devices are why regulated smokestacks and tailpipes emit far less pollution than they once did.

Pollutant removal by a control device

mass removed = input mass × efficiency ; mass emitted = input mass × (1 − efficiency)

Express efficiency as a decimal (98% = 0.98). A 98%-efficient device still lets 2% of the pollutant escape.

Worked example

A coal plant’s flue gas carries 500 kg of particulate matter per day. An electrostatic precipitator removes 98% of it. How much particulate matter is removed, and how much escapes into the air each day?

1.Convert efficiency to a decimal: 98% = 0.98.
2.Mass removed = input × efficiency = 500 kg × 0.98 = 490 kg per day.
3.Mass emitted = input × (1 − efficiency) = 500 kg × 0.02 = 10 kg per day.
4.Check: removed + emitted = 490 + 10 = 500 kg, the full input.

Answer: 490 kg is captured and 10 kg still escapes each day. Even a highly efficient 98% device releases some pollution, which is why standards keep tightening.

Checkpoint

A naturally occurring radioactive gas that seeps from soil and rock into the basements of homes and is a leading cause of lung cancer is:

Tip

Match each control device to its target pollutant: scrubbers → SO₂, electrostatic precipitators and baghouse filters → particulates, catalytic converters → vehicle CO/NOₓ/hydrocarbons. Exam questions often ask which device to install to fix a specific pollutant.

Checkpoint

A smokestack emits 1,000 kg of sulfur dioxide per day. A scrubber is installed that removes 90% of the SO₂. How much SO₂ still escapes into the atmosphere each day?

On the exam

For removal-efficiency problems, watch whether the question asks for the amount removed (input × efficiency) or the amount emitted (input × (1 − efficiency)). They are easy to swap. A quick check: removed + emitted should equal the total input.

Answer the 2 checkpoints as you read.