Reducing pollution and protecting yourself

What does the AQI number on your phone mean?

On a smoggy morning your phone shows 'AQI 320'. Should you go for a run, wear a mask, or stay in? And what are scientists doing to bring that number down?

Trees help: in photosynthesis, chlorophyll and sunlight turn carbon dioxide and water into glucose and oxygen, and dust settles on leaves and bark. A three-way catalytic converter in a car turns nitrogen oxides back into nitrogen and oxygen, and oxidises carbon monoxide and unburnt hydrocarbons to carbon dioxide and water.

Sulphur dioxide is cut by burning low-sulphur fuels, or by flue gas desulphurisation, where calcium oxide removes up to 95% of the SO₂ from power-station waste gases. Renewable energy from the Sun, wind, water, geothermal heat and biomass reduces the need for fossil fuels.

The Air Quality Index rates the air: under 50 is good, and the risk rises with the number; over 300 is hazardous. Children, the over-65s, outdoor workers and people with heart or lung disease or diabetes face the most risk. On bad days: stay out less, wear a fitted N95 mask, close windows and fit a CO detector.

Cut pollution at the source (converters, low-sulphur fuel, renewables, trees) and protect yourself when the AQI is high.

Key terms

Catalytic converter

Cleaner car exhaust.

Flue gas desulphurisation

Cutting acid rain.

Renewable resource

Replacing fossil fuels.

Air Quality Index

Deciding how to protect yourself.

Short questions with model answers

1. Q1. How can the CO in car exhaust be reduced? (Constructed response iv, p. 144)

   • Why CO forms
   • 2CO + O₂ → 2CO₂

   Fit a three-way catalytic converter, which oxidises CO to CO₂.

2. Q2. Write the photosynthesis equation from the book and say how it helps the air.

   • 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
   • Check

   Plants take carbon dioxide out of the air and release oxygen.

Common mistakes

• ✗ A higher AQI means cleaner air.

  ✓ The higher the number, the higher the risk; under 50 is good (p. 141).

• ✗ Any mask protects you from particulate matter.

  ✓ Not all do; a well-fitted N95 filters better (p. 141).

• ✗ A catalytic converter removes carbon dioxide.

  ✓ CO₂ passes through unchanged; the converter makes CO₂ from CO (Exercise iv).

MCQs

1. 1. Which substance remains unaffected in a car's catalytic converter? (Exercise iv, p. 143)

   1. (a) CO₂
   2. (b) CO
   3. (c) NO
   4. (d) NO₂
   Show answer

   (a) It is a product, not changed further (p. 140).

2. 2. Which people are most affected by air pollution? (Exercise v, p. 143)

   1. (a) Young adults
   2. (b) Middle-aged people
   3. (c) Children
   4. (d) Both children and aged people
   Show answer

   (d) Under 18 and over 65 (p. 141).

3. 3. Which catalyst is used in car catalytic converters? (Exercise viii, p. 143)

   1. (a) Ni
   2. (b) Cu
   3. (c) Pt, Pd and Rh
   4. (d) CaO
   Show answer

   (c) Chapter 9, p. 123.

4. 4. An AQI over which value is considered hazardous?

   1. (a) 50
   2. (b) 100
   3. (c) 200
   4. (d) 300
   Show answer

   (d) p. 141.

5. 5. In flue gas desulphurisation, what removes SO₂?

   1. (a) Calcium oxide
   2. (b) Sodium chloride
   3. (c) Platinum
   4. (d) Water only
   Show answer

   (a) Up to 95% (p. 140).

Quick revision

• Trees, catalytic converters, low-sulphur fuels, desulphurisation and renewables all cut pollution.
• AQI under 50 is good; over 300 is hazardous.
• On bad days: less time outside, N95 mask, closed windows, CO detector at home.