Earth and atmosphere, Year 11: pollutants from burning fuels

incomplete

HintThe carbon ends up only partly oxidised.

The whyWith plenty of oxygen the carbon in a fuel becomes carbon dioxide, CO2. With too little, some of it becomes carbon monoxide, CO, and some is left as particles of carbon (soot).

Sulfur in the fuel reacts with oxygen as the fuel burns

HintCoal and some oils contain an impurity that is a yellow element.

The whyS + O2 → SO2. Most fuels are mainly carbon and hydrogen, but some, including coal, also contain sulfur compounds. When the fuel burns the sulfur is oxidised too.

Nitrogen and oxygen from the air react at the high temperature inside the engine

HintAbout four-fifths of what a car draws in is one normally unreactive gas.

The whyNitrogen is unreactive at ordinary temperatures, but inside an engine or a furnace it is hot enough for it to combine with oxygen, for example N2 + O2 → 2NO.

Soot

HintIt is the black powder that collects inside chimneys.

The whyIt forms during incomplete combustion, when there is too little oxygen for all the carbon in the fuel to be oxidised. Together with unburned hydrocarbons it makes up the particulates released into the air.

water; sulfur dioxide

HintWork out what each of the three elements in the fuel becomes once it has joined with oxygen.

The whyIn plenty of air every element in the fuel is fully oxidised: carbon to carbon dioxide, hydrogen to water and sulfur to sulfur dioxide. Because oxygen is not in short supply, no carbon monoxide or soot is expected.

Carbon monoxide

HintIts formula has one fewer oxygen atom than the gas we breathe out.

The whyBecause it cannot be seen or smelt it is not easily detected, so a person can breathe in a harmful amount without knowing. That is why homes with gas, oil or solid-fuel heaters are fitted with detectors.

Sulfur dioxide and oxides of nitrogen

HintBoth are compounds of a non-metal joined to oxygen, and they dissolve in rainwater.

The whyThey react with water and oxygen in the air to form acids, which fall in the rain. Acid rain damages trees, harms life in lakes and rivers, and attacks limestone buildings and metal structures.

Global dimming

HintThe second word describes what happens when you turn a lamp down.

The whyParticles of soot and other solids reflect and absorb sunlight before it reaches the ground. It is a different effect from global warming and has a different cause.

They cause breathing (respiratory) problems

HintThink about which organs meet polluted air first.

The whyBoth gases irritate the airways and the lungs, and can make conditions such as asthma worse. This is one reason why sulfur is removed from fuels and why vehicle exhausts are cleaned.

Health problems for humans, for example damage to the lungs

HintConsider what happens when very fine dust is inhaled.

The whyThe particles are small enough to be carried deep into the lungs. Increased amounts in the air, for example near busy roads, are linked to more illness.