Man made Sources of Air Pollution MCQ - Practice Questions with Answers

1. Gases:

• Gases produced during fuel combustion are CO, CO₂, SO₂, various oxides of nitrogen (NO, NO₂, N₂O₄) and assorted hydrocarbons. 
• Carbon monoxide (CO) is produced due to incomplete combustion of the carbon content of fossil fuels. 
• Carbon dioxide (CO₂) is produced due to complete combustion of carbon content.
• Hydrogen sulphide (H₂S) is produced from refineries, sewage treatment and pulp mills. CO alone contributes to 47% air pollution. 
• SO₂ is produced due to burning of coal and oil and from industrial processes. 
• Nitrogen oxides are formed when fuel is burnt at very high temperature such as in industrial plants and transportation vehicles. 
• Nitrogen monoxide (NO) is produced during combustion in the engine cylinder.
• When this gas passes out of the engine, it cools down and combines with more oxygen to form NO₂ and N₂O₄. This mixture of gases is generally called oxides of nitrogen (NOx). 
• Ozone (O₃) is another air pollutant which is a major component of photochemical smog which is formed from NOx, VOCs and oxygen in the presence of sunlight and heat.

2. Particulate Matters:

• These are solid particles and liquid droplets suspended in air. 
• They may be settled down where particle size is more than 10 μm or remain suspended in air when particle size is below 10 μm.
• Particulate matter in the size range of 0.01 μm to 50 μm or less in size, aerosols (less than 1 μm) flash and dust 0.25 to 500 μm), grit (more than 500 μm).
• Particulate matter below 5 μm size is usually deposited in the respiratory tract. 
• Smoke and fog reduce air visibility, photosynthetic efficiency of plants and cause respiratory distress and allergy in human beings.

3. Secondary Pollutants:

• These are formed from primary pollutants through a wide range of photochemical reactions and cause greater damage than primary pollutants.
• When hydrocarbons from exhaust are exposed to light, alkanes, ethylenes, unsaturated hydrocarbons, aldehydes and aromatics are formed. 
• One of these compounds is benzopyrene which induces cancer in man. 
• Two other photochemically originated pollutants are peroxybenzoic nitrate and peroxyacetyl nitrate (PAN).
• Some other secondary pollutants for air pollution are sulphur dioxide and sulphuric acid mist, NO, NO₂, and HNO₃.
• The word smog was first used in 1905 to describe the combination of smoke and fog in London which totally obscured visibility for a few hours. 
• This smog resulted from SO₂, soot and tarry materials released into the atmosphere by burning of high-sulphur coal.