Air pollutionIB MYP Chemistry: Revision notes
Section 1
Air pollutants and where they come from
Burning fuels in vehicles, power stations and homes releases pollutants into the air. The four main ones are:
- carbon monoxide (CO): from incomplete combustion of fuels, mainly in vehicle engines
- sulfur dioxide (SO₂): from burning fuels that contain sulfur, such as coal in power stations
- nitrogen oxides (NOₓ): formed when nitrogen and oxygen from the air react at the high temperature in engines
- particulates: tiny solid particles, such as unburnt carbon (soot), mainly from diesel engines and burning wood and coal
Nitrogen oxides are not made from nitrogen in the fuel, because fuels contain very little nitrogen.
Section 2
Effects of each pollutant
- Carbon monoxide is toxic: it combines with haemoglobin so the blood carries less oxygen. It causes headaches, dizziness and, at high levels, death.
- Sulfur dioxide dissolves in rain to form sulfuric acid, so it causes acid rain. It also causes breathing problems such as asthma.
- Nitrogen oxides cause breathing problems and also form acid rain (nitric acid). They contribute to smog.
- Particulates get deep into the lungs and cause breathing problems and heart disease. They also make buildings dirty.
Link each pollutant to its source and its effect: for example nitrogen oxides, from hot engines, give acid rain and breathing problems.
Section 3
Acid rain
Sulfur dioxide and nitrogen oxides dissolve in rain water to form sulfuric and nitric acids. Acid rain lowers the pH of lakes and soil, harming fish and trees, and reacts with limestone and marble because they are made of calcium carbonate:
calcium carbonate + sulfuric acid → calcium sulfate + water + carbon dioxide
It also makes metals corrode faster. Wind carries the gases far from where they were made, so the damage can be in another country.
Section 4
Reducing pollution from vehicles
A catalytic converter is fitted to the exhaust of a car. Its honeycomb is coated with metal catalysts such as platinum and rhodium. It changes harmful gases into less harmful ones:
carbon monoxide + nitrogen monoxide → carbon dioxide + nitrogen
It also changes unburnt fuel into carbon dioxide and water. It does not remove carbon dioxide, which is a greenhouse gas.
Other ways to cut vehicle pollution: filters to trap particulates in diesel exhaust, cleaner fuels, electric vehicles, public transport, cycling and walking.
Section 5
Reducing pollution from power stations
Sulfur dioxide can be reduced in two ways:
- remove sulfur from the fuel before it is burned
- remove sulfur dioxide from the chimney gases: the gases pass through calcium carbonate or calcium oxide, which reacts with sulfur dioxide to form a solid, calcium sulfite (flue gas desulfurisation)
Another option is to use less coal by changing to renewable energy.
Section 6
Weighing up the impacts
Pollution control questions ask you to evaluate. Include benefits (cleaner air, fewer illnesses, less damage to forests and buildings) and drawbacks (cost, higher prices, waste produced, carbon dioxide still released). Link them to social, economic and environmental effects, then give a justified conclusion.
Do not say a catalytic converter stops all pollution. It removes carbon monoxide and nitrogen oxides, but carbon dioxide is still released.
That's the notes covered.
Carry on to the next subtopic.
Exam questions on Air pollution
- An air-quality monitoring station beside a busy road in Mexico City records high levels of carbon monoxide, nitrogen oxides and particulates at rush hour. Most of the vehicles on the road use petrol or diesel engines.Describe two harmful effects of nitrogen oxides.2 marks
- A student in Seoul compares particulate pollution at four sites. At each site she fixes a clean microscope slide, coated in a thin layer of petroleum jelly, to a post 1.5 m above the ground and leaves it for seven days. She then counts the dark particles stuck to a 1 cm² area of each slide. The counts are: roadside 48, school playground 20, park 9 and a hill 3 km from any road 6.Describe the pattern in the results and suggest a reason for it.2 marks
- In many countries new petrol cars must be fitted with a catalytic converter. This is a metal honeycomb coated with platinum and rhodium, which the hot exhaust gases pass through before leaving the car.Write a word equation for the reaction in a catalytic converter that changes carbon monoxide and nitrogen monoxide into less harmful gases, and explain why the products are less harmful.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).