11.3.2 Human Activities

• Coal
• Petroleum
• Natural gas

Nearly half of the air pollution comes from cars and other motor vehicles.

Factories and power plants that burn coal or oil release poisonous gases in the air.

• Carbon monoxide (CO)
• Nitrogen oxides (NO, NO₂)
• Sulphur oxides (SO₂, SO₃)

Simple explanation: Human activities — especially burning fossil fuels in vehicles, factories, and power plants — are the main cause of air pollution.

Chemical Equations from the Book

1. Incomplete combustion of carbon (produces CO):

C_(s) + O_2(g) (limited) → CO_(g)

2. Burning of sulphur (produces SO₂):

S_(s) + O_2(g) → SO_2(g)

3. Formation of nitric oxide (NO):

N_2(g) + O_2(g) → 2NO_(g)

4. Oxidation of NO to NO₂:

2NO_(g) + O_2(g) → 2NO_2(g)

Simple explanation: These equations show how pollutants like CO, SO₂, and NOₓ are formed during combustion.

Table 11.1: Effects Produced by Air Pollutants

Simple explanation: This table summarises the properties, sources, and effects of the three main air pollutants.

Concept Assessment Exercise 11.4 (from the Book)

1. Write three human activities that are responsible for air pollution.

• Burning fossil fuels in vehicles
• Burning fossil fuels in factories and power plants
• Incineration (burning of waste)

2. Write three natural processes that are contributing to air pollution.

• Forest fires
• Volcanic eruptions
• Dust storms

3. List main sources of the following air pollutants:

(a) SO₂ — Burning fossil fuels (coal, petroleum) in power stations and industries (b) CO — Incomplete combustion of fossil fuels in vehicles and residential heating (c) NOₓ — Exhaust fumes of motor vehicles, power stations, and industries using fossil fuels

Intermediate Level

Natural Sources in Detail

Human Activities in Detail

Why Fossil Fuels Are the Main Problem

• Carbon — produces CO and CO₂ when burned.
• Sulphur — produces SO₂ when burned.
• Nitrogen — produces NOₓ at high temperatures.

When these fuels are burned, they release these pollutants into the air.

Simple explanation: Fossil fuels contain impurities (sulphur, nitrogen) that become pollutants when burned.

The Role of Vehicles

• Nearly half of air pollution comes from cars and other motor vehicles.
• Vehicle exhaust contains: CO, NOₓ, unburned hydrocarbons, particulates.
• This is why catalytic converters are important (covered in Section 11.6).

Industrial Sources

• Sulphur dioxide (SO₂) — from sulphur in the fuel.
• Nitrogen oxides (NOₓ) — from high-temperature combustion.
• Carbon monoxide (CO) — from incomplete combustion.
• Particulate matter — soot, ash, dust.

Important Points

• - Air pollution: air that contains harmful particles and gases.
• - Natural sources: forest fires, dust storms, volcanoes, termites, cows, electrical discharges.
• - Human activities: burning fossil fuels, vehicles, factories, power plants, incineration.
• - Fossil fuels: coal, petroleum, natural gas.
• - Nearly half of air pollution comes from cars and other motor vehicles.
• - Pollutants from combustion: CO, NOₓ, SOₓ.
• - Table 11.1: summarises the properties, sources, and effects of CO, SO₂, and NOₓ.
• - Natural sources of specific pollutants:
• - Volcanoes → SO₂, dust, ash
• - Termites and cows → CH₄
• - Lightning → NOₓ
• - Forest fires and dust storms → smoke, dust

Remember

• - Natural sources: forest fires, dust storms, volcanoes, termites, cows, lightning.
• - Human activities: burning fossil fuels, vehicles, factories, power plants.
• - Nearly half of air pollution comes from motor vehicles.
• - Fossil fuels: coal, petroleum, natural gas.
• - Pollutants from combustion: CO, NOₓ, SOₓ.
• - Volcanoes → SO₂, dust, ash.
• - Termites and cows → CH₄.
• - Lightning → NOₓ.

Common Mistakes

• 1. Thinking all air pollution is caused by humans. Some pollution is natural (volcanoes, forest fires).
• 2. Forgetting that vehicles are a major source. Nearly half of air pollution comes from motor vehicles.
• 3. Thinking CO₂ is the only greenhouse gas. Other gases like CH₄ and NOₓ also contribute.
• 4. Confusing the sources of different pollutants.
• - SO₂ → burning fossil fuels
• - CO → incomplete combustion
• - NOₓ → vehicle exhaust, high-temperature combustion
• - CH₄ → decomposition, livestock
• 5. Thinking volcanoes only release dust. They also release poisonous gases like SO₂.
• 6. Forgetting that lightning produces NOₓ. Electrical discharges in the atmosphere produce nitrogen oxides.

Quick Revision

• Air pollution: air that contains harmful particles and gases is said to be polluted.
• Natural sources:
• Forest fires and dust storms → smoke, dust
• Volcanoes → dust, poisonous gases (SO₂), ash
• Termites and cows → methane
• Electrical discharges (lightning) → nitrogen oxides
• Human activities:
• Burning fossil fuels (coal, petroleum, natural gas)
• Vehicles (cars and other motor vehicles) — nearly half of air pollution
• Factories and power plants
• Incineration
• Pollutants from burning fossil fuels: carbon monoxide (CO), nitrogen oxides (NO, NO₂), sulphur oxides (SO₂, SO₃).
• Chemical equations:
• C(s) + O₂(g) (limited) → CO(g)
• S(s) + O₂(g) → SO₂(g)
• N₂(g) + O₂(g) → 2NO(g)
• 2NO(g) + O₂(g) → 2NO₂(g)
• Table 11.1: properties, sources, and harmful effects of CO, SO₂, and NOₓ.

60-Second Revision

• Natural sources: forest fires, volcanoes, termites, cows, lightning.
• Human activities: burning fossil fuels, vehicles, factories, power plants.
• Nearly half of air pollution comes from motor vehicles.
• Volcanoes → SO₂; cows → CH₄; lightning → NOₓ.
• Warning: air pollution comes from both natural and human sources.