Air Quality And Climate

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Notes

Composition of Air

The composition of clean, dry air is approximately **78% nitrogen** and **21% oxygen**.
The remaining gases include **carbon dioxide** and trace quantities of **noble gases** (e.g., argon, neon).
This composition has remained relatively unchanged for about 200 million years.

Air Pollutants and Their Sources

**Carbon dioxide (CO₂)** is produced by **complete combustion** of carbon-containing fuels (e.g., CH₄ + 2O₂ → CO₂ + 2H₂O).
**Carbon monoxide (CO)** is produced by **incomplete combustion** (e.g., 2C₈H₁₈ + 10O₂ → 5CO + 3CO₂ + 9H₂O) and is **toxic** as it binds to haemoglobin, preventing oxygen transport.
**Particulates (soot, C)** are also from incomplete combustion (e.g., CH₄ + O₂ → C + 2H₂O) and cause **respiratory problems** and **cancer**.
**Methane (CH₄)** comes from **digestive processes** of animals, decomposition of vegetation, and bacterial action in swamps, rice paddies, and landfill sites.
**Oxides of nitrogen (NOₓ)** form when N₂ and O₂ react at high temperatures (e.g., in car engines, furnaces, lightning) and cause **acid rain** and **photochemical smog**.
**Sulfur dioxide (SO₂)** is produced by burning **fossil fuels containing sulfur** (e.g., S + O₂ → SO₂) and causes **acid rain**.

Effects of Air Pollutants

**CO₂** and **methane** are **greenhouse gases** that contribute to **global warming** and **climate change**.
**CO** is **poisonous** – it combines with haemoglobin, reducing oxygen carriage in the blood.
**Particulates** cause **respiratory problems** and **cancer**.
**NOₓ** and **SO₂** dissolve in rainwater to form **acid rain**, which corrodes metal structures, damages carbonate rocks/buildings, harms aquatic life, and pollutes crops/water.
**NOₓ** also irritates lungs, throats, and eyes, and contributes to **photochemical smog**.

The Greenhouse Effect and Global Warming

The **greenhouse effect** is a natural process: the Sun's radiation warms Earth, and **greenhouse gases** (CO₂, CH₄) trap some **infrared radiation** emitted from the surface, keeping the planet warm.
**Enhanced greenhouse effect** occurs when increased concentrations of greenhouse gases trap more thermal energy, leading to **global warming**.
Consequences of global warming include **rising sea levels** (from melting glaciers), **extreme weather**, **habitat loss**, **species extinction**, **migration of species**, and **spread of diseases**.

Reducing Climate Change

Reduce **CO₂ emissions** by using **renewable energy** (solar, wind, hydrogen), **fuel-efficient vehicles** (electric/hybrid), **public transport**, **recycling**, and reducing household energy use.
**Planting trees** (reforestation) removes CO₂ via **photosynthesis**.
Reduce **methane emissions** by decreasing **livestock farming** (methane from digestion).

Reducing Acid Rain

Use **low-sulfur fuels** to reduce SO₂ emissions.
**Flue gas desulfurisation** (FGD) in power stations: waste gases are sprayed with a **lime slurry** (calcium oxide/carbonate) which reacts with SO₂ to form **calcium sulfate**, removing 90–95% of SO₂.
**Catalytic converters** in vehicles remove **oxides of nitrogen** by redox reactions: $2NO + 2CO$ → N₂ + 2CO₂.

Catalytic Converters (Extended Tier Only)

Catalytic converters contain **platinum** and **rhodium** catalysts on a **honeycomb** structure to increase surface area.
They convert **CO** to **CO₂** (2CO + O₂ → 2CO₂), **NOₓ** to **N₂** (2NO → N₂ + O₂), and **unburned hydrocarbons** to CO₂ and H₂O (e.g., C₈H₁₈ + 12½O₂ → 8CO₂ + 9H₂O).

States of matter: solid, liquid, gas. Not directly about air quality but can illustrate gas particles in the atmosphere.

Practice questions

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1.What is the approximate percentage of nitrogen in clean, dry air?
Easy
- A21%
- B78%
- C1%
- D0.04%
2.Which gas is produced by the complete combustion of carbon-containing fuels?
Easy
- Acarbon monoxide
- Bcarbon dioxide
- Cmethane
- Dsulfur dioxide
3.Carbon monoxide is toxic because it combines with haemoglobin in the blood and prevents it from carrying oxygen.
Easy
True or false?
4.State one adverse effect of particulates (soot) on human health.
Medium
5.Complete the sentence about the greenhouse effect.
Medium
Greenhouse gases such $as ____ and ____$ absorb thermal energy and re-emit it, trapping heat in the atmosphere.
6.Match each pollutant to its primary source.
Medium
- Sulfur dioxide
- Oxides of nitrogen
- Methane
- Combustion of fossil fuels containing sulfur
- High temperature reactions in car engines
- Digestive processes of animals
7.The complete combustion of methane produces carbon dioxide and water. How many moles of oxygen are required to completely combust 2 moles of methane? $(Equation: CH4 + 2O2$ → $CO2 + 2H2O)$
Hard
- A4
- B3
- C6
- D5
8.Name one strategy to reduce carbon dioxide emissions from vehicles.
Medium

Slides

Composition of Clean, Dry Air

The composition of gases in the atmosphere has not changed much in 200 million years.
Clean, dry air is approximately 78% nitrogen and 21% oxygen.
The remaining gases include carbon dioxide and trace quantities of noble gases.

What is the approximate percentage of oxygen in clean, dry air?

78%
21%
1%
0.04%

Air Pollutants and Their Sources

Carbon dioxide: complete combustion of carbon-containing fuels (e.g., fossil fuels).
Carbon monoxide: incomplete combustion of fuels; toxic, binds to haemoglobin.
Particulates (soot): incomplete combustion; cause respiratory problems and cancer.
Methane: digestive processes of animals, decomposition, landfill sites.
Oxides of nitrogen: high-temperature reactions in car engines and furnaces; cause acid rain.
Sulfur dioxide: combustion of fossil fuels containing sulfur; causes acid rain.

Which of these are sources of sulfur dioxide?

Combustion of fossil fuels containing sulfur compounds
Incomplete combustion of methane
Power stations burning coal
Reaction of nitrogen with oxygen in car engines

Acid Rain Formation

Sulfur dioxide and oxides of nitrogen dissolve in rainwater to form acid rain.
Acid rain corrodes metal structures, buildings and statues made of carbonate rocks.
It damages aquatic organisms and causes respiratory problems.

Acid rain is caused $by ____ and ____$ dissolving in rainwater.

The Greenhouse Effect

The Sun emits radiation that enters Earth's atmosphere.
Some energy is reflected; the Earth's surface absorbs and re-emits thermal energy (infrared).
Greenhouse gases (CO2, methane) absorb some thermal energy and re-emit it, trapping heat.
This keeps Earth warm; increased concentrations lead to global warming (enhanced greenhouse effect).

Which of these is a greenhouse gas?

Nitrogen
Oxygen
Carbon dioxide
Argon

Consequences of Global Warming

Climate change: rising temperatures alter weather patterns.
Rising sea levels: glaciers melt, causing flooding in low-lying areas.
Extinction of species: habitats destroyed by changing conditions.
Migration of species: move to more habitable areas.
Spread of diseases: warmer climate allows disease vectors to expand.

Which of these are consequences of global warming?

Rising sea levels
Increased oxygen levels
Extinction of species
More frequent droughts

Reducing Carbon Dioxide Emissions

Use renewable energy (solar, wind) instead of fossil fuels.
Use fuel-efficient vehicles (electric/hybrid cars).
Reduce number of vehicles: public transport, car-sharing.
Recycle/reuse products made from crude oil.
Reduce household energy consumption.
Reduce deforestation and plant more trees (photosynthesis absorbs CO2).

Which of the following helps reduce carbon dioxide emissions?

Burning more coal
Planting trees
Using more cars
Increasing deforestation

Reducing Methane Emissions

Methane is produced during digestion in livestock.
Reducing livestock farming can lower methane emissions.

Methane emissions can be reduced by decreasing the amount $of ____$ farming.

Reducing Acid Rain: Sulfur Dioxide

Use low-sulfur fuels.
Flue gas desulfurisation: spray waste gases with calcium oxide/calcium carbonate slurry.
Calcium compounds react with SO2 to form calcium sulfate, removing 90-95% of SO2.

What is the main method to reduce sulfur dioxide emissions from power stations?

Using catalytic converters
Flue gas desulfurisation
Planting trees
Using electric cars

Catalytic Converters (Extended Tier)

Catalytic converters in vehicles remove oxides of nitrogen, carbon monoxide, and unburned hydrocarbons.
They contain platinum and rhodium catalysts in a honeycomb to increase surface area.
Redox reactions: CO oxidised to CO2; NOx reduced to N2; hydrocarbons oxidised to CO2 and H2O.
Example: $2NO + 2CO$ → $N2 + 2CO2$ .

In a catalytic converter, carbon monoxide is oxidised $to ____ and$ oxides of nitrogen are reduced $to ____$ .

Summary of Air Quality and Climate

Main air pollutants: CO2, CO, particulates, CH4, NOx, SO2.
Greenhouse gases cause global warming and climate change.
Acid rain is caused by SO2 and NOx.
Reduction strategies: renewable energy, low-sulfur fuels, catalytic converters, flue gas desulfurisation.

Flashcards

What is the approximate composition of clean, dry air?

78% nitrogen, 21% oxygen, and the remaining gases include carbon dioxide and trace quantities of noble gases.

What are the main sources of carbon dioxide in the atmosphere?

Complete combustion of carbon-containing fuels such as fossil fuels (e.g., methane: $CH4 + 2O2$ → $CO2 + 2H2O)$ .

What adverse effect does carbon dioxide have on the environment?

It increases global warming, which leads to climate change.

How is carbon monoxide produced and what is its adverse effect?

It is produced by incomplete combustion of carbon-containing fuels. It is toxic, as it combines with haemoglobin in the blood and prevents it from carrying oxygen.

What are particulates and what are their adverse effects?

Particulates are particles of carbon (soot) produced by incomplete combustion. They cause respiratory problems and cancer.

What are the sources of methane?

Waste gases from digestive processes of animals, decomposition of vegetation, and bacterial action in swamps, rice paddy fields, and landfill sites.

How are oxides of nitrogen formed and what are their adverse effects?

They are formed when nitrogen and oxygen react at high temperatures (e.g., in car engines). They produce photochemical smog, acid rain, and cause respiratory problems.

What is the main source of sulfur dioxide and its adverse effect?

Combustion of fossil fuels containing sulfur compounds $(e.g., S + O2$ → SO2). It dissolves in rain to form acid rain, which corrodes structures and damages aquatic life.

What is the difference between complete and incomplete combustion of hydrocarbons?

Complete combustion in excess oxygen produces CO2 and H2O. Incomplete combustion in oxygen-deficient conditions produces CO, H2O, and sometimes carbon particulates.

Explain the greenhouse effect.

The Sun's energy enters the atmosphere; some is reflected, some is absorbed by Earth and re-emitted as infrared radiation. Greenhouse gases (e.g., CO2, methane) absorb some of this thermal energy and re-emit it, trapping heat and keeping Earth warm.

What is the enhanced greenhouse effect?

The increase in concentration of greenhouse gases due to human activity, which traps more thermal energy and causes global warming.

List three consequences of global warming.

Rising sea levels due to melting glaciers, extinction of species due to habitat destruction, and migration of species to more habitable areas.

How can carbon dioxide emissions be reduced?

By using renewable energy (solar, wind), fuel-efficient vehicles, reducing vehicle use, recycling, reducing energy consumption, and planting trees (reforestation).

How can methane emissions be reduced?

By reducing the amount of livestock farming, as methane is produced during digestion in animals.

What are two strategies to reduce acid rain?

Using catalytic converters in vehicles to remove oxides of nitrogen, and flue gas desulfurisation to remove sulfur dioxide from power station emissions.

Describe flue gas desulfurisation.

Waste gases from coal-fired power stations are sprayed with a wet slurry of calcium oxide and calcium carbonate, which react with sulfur dioxide to produce calcium sulfate, removing 90-95% of SO2.

What is the function of a catalytic converter?

It converts harmful exhaust gases (oxides of nitrogen, carbon monoxide, unburned hydrocarbons) into less harmful substances (N2, CO2, H2O) using redox reactions on transition metal catalysts.

Write the equation for the reaction of nitrogen monoxide with carbon monoxide in a catalytic converter.

$2NO + 2CO$ → $N2 + 2CO2$

What are the products of complete combustion of a hydrocarbon?

Carbon dioxide and water.

What are the products of incomplete combustion of methane?

Carbon monoxide and water, or carbon (soot) and water, depending on oxygen availability.

Why is carbon monoxide dangerous to humans?

It combines with haemoglobin in the blood, preventing oxygen transport.

What is the source of particulates?

Incomplete combustion of carbon-containing fuels, such as fossil fuels.

Name two greenhouse gases.

Carbon dioxide and methane.

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