C1 Air Quality- chemicals in the air

The earth atmosphere is a mixture of gases, these are as follows:

• Nitrogen 78%
• Oxygen 21%
• Argon 1%
• Carbon dioxide 0.04%
• and variable amounts of water vapour.

Aswell as these, human activities add harmful chemicals (pollutants) to the air.

Coal (which is mainly carbon) and petrol and diesel (which are mainly hydrocarbons (compounds made up of hydrogen and carbon only)) burn in fossil fuel stations, and vehicles to create electricity, this is an example of combustion.

Combustion is where fuels react with oxygen, an example of this is below with methane as the fuel:

• Methane (CH4) reacts with 2 oxygen (O2) atoms and makes carbon dioxide (CO2) and 2 water (H2O) atoms
• The number of atoms at the start are as follows: 1 carbon (C) atom, 4 hydrogen (H) atoms and 4 oxygen (O) atoms.
• the number of atoms at the end are as follows: 1 carbon (C) atom, 4 hydrogen (H) atoms and 4 oxygen (O) atoms.

In all chemical reactions the atoms are rearranged.

The same atoms are present in both the products and the reactants, the only difference is that they are joined together differently. This is called the conservation of atoms.

The properties of the reactants in a chemical reaction are very different to that of the products. Some products of hydrocarbon combustion are pollutants.

The following chemicals are air pollutants:

• Sulphur dioxide (SO2)
• Nitrogen monoxide (NO)
• Nitrogen dioxide (NO2)
• Carbon monoxide (CO)
• Carbon Dioxide (CO2)
• Particulates (small particles of solid) for example carbon (C)

The following are all examples of how pollutants are released into the air:

• Through incomplete combustion*- this makes carbon monoxide and solid carbon.
• When fuel burns**, this makes sulphur dioxide.
• In engines when oxygen and nitrogen react together***, this makes nitrogen oxides.

*Fossil fuels burn to make carbon dioxide. Sometimes there is not enough oxygen to convert all the carbon in the fuel to carbon dioxide. This is incomplete combustion

**Some fossil fuels contain sulphur impurities. When the fuel burns, the sulphur reacts with oxygen to make sulpher dioxide.

***Nitrogen monoxide forms first. This reacts with more oxygen from the air to make nitrogen dioxide, in other words nitrogen monoxide is oxidized. Together NO and NO2 are called NOX.

Below is what happens to certain pollutants after they are produced:

• Particulate carbon makes surfaces dirty and can cause health problems if breathed in.
• CO is poisonous.
• CO2 dissolves in rainawater and seawater, plants use it for photosynthesis. CO2 in the atmosphere contributes to global warming.
• SO2 and NO2 react with water and oxygen to make acid rain. NO2 may increase the risk of asthma attacks.

The only way to produce less CO2 is to burn less fossil fuel.

We can reduce air pollution from fossil fuel stations by:

• Using less electricity,
• Removing sulphur impurities from fuels before burning them,
• Removing sulphur dioxide and particulates (carbon and ash) from the gases that power stations emit.

We can reduce air pollution from vehicle exhaust gases by:

• Developing efficient engines that burn less fuel,
• Using low sulphur fuels
• Using catalytic converters to convert nitrogen monoxide to nitrogen and oxygen and carbon monoxide into carbon dioxide,
• Using public transport instead of cars,
• Having legal limits on exhaust emmissions.