Earth and atmosphere, Year 11: pollutants from burning fuels

incomplete

提示The carbon ends up only partly oxidised.

为什么With 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

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

为什么S + 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

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

为什么Nitrogen 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

提示It is the black powder that collects inside chimneys.

为什么It 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

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

为什么In 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

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

为什么Because 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

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

为什么They 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

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

为什么Particles 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

提示Think about which organs meet polluted air first.

为什么Both 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

提示Consider what happens when very fine dust is inhaled.

为什么The 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.