C1-Air quality



Air (atmosphere) is a mixture of gases: mainly nitrogen, oxygen and argon it also contains small amounts of water vapour and carbon dioxide.

Clouds are water and dust is a solid so they are not part of the air.

Gases spread out to take up all the space available.

Perticles are very small so in gases there is alot of space between gas molecules, so they can be squeezed into a smaller volume.

Dry air contains:

  • 78% Nitrogen
  • 21% Oxygen
  • 1% Argon
  • Small amounts of other gases

Oxygen reacts with most metals to make solid metal oxides.

We can find the amount of oxygen in air by passing air over heated copper.

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The Earths atmosphere

The Earths atmosphere was probably formed about 4 billion years ago by gases from volcanoes. Volcanoes release huge amounts of carbon dioxide, water vapour, lava and dust.

Different processes have removed almost all of the Carbon dioxide that was in the early atmosphere:

  • 4 billion years ago the Earths atmosphere was very hot.
  • As the Earth cooled oceans formed from the condensed water.
  • About 3 billion years ago small bacteria-like creatures evolved to use photosynthesis.
  • Carbon dioxide was formed from plants and animals dying and becoming buried.
  • Over millions of years some buried materials became fossil fuels.
  • Carbon dioxide dissolved in oceans reacted with salts to form insoluble calcium carbonate.
  • This formed sediments which became buried and cemented to form sedimentary rocks.

Sixty years ago many scientists thought the early atmosphere was mainly ammonia and methane.

Recent rock composition discoveries showed early ideas were not correct and the early atmosphere was mainly carbon dioxide.

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Human activity and air quality

Humans are changing the gases in the atmosphere by burning fuels.

Gases called pollutants are harmful to health, e.g. cabon monoxide, nitrogen oxides and sulfur dioxide.

Pollutants are harmful to the environment and to the people and animals living there, e.g. Carbon monoxide reduces the amount of oxygen blood can carry.

Air quality is good if there are few pollutants and poor if there are lots of pollutants.

Burning fuels releases carbon dioxide and solid particulates that float in the air e.g. Carbon (soot). Particulates are also naturally released by volcanoes as ash.

In the last 50 years the amount of carbon dioxide in the air has increased by 25%.

Carbon dioxide is linked to climate change, by acting as a 'greenhouse' trapping heat in the atmosphere.

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Human activity and air quality

Human activity like burning down forests to make more farmland, increases carbon dioxide and particulates.

When air pollution levels are high, more deaths from asthma, heart disease and lung cancer occur. There is a correlation between air quality and health.

Air quality is more of a problem in large cities, such as mexico city and beking. Some countries have laws to improve air quality.

Sulfur dioxide and nitrogen dioxide are pollutants that make acid rain, which damage plants and animals.

Sulfur dioxide and nitrogen oxides are asthma triggers for some people.

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Measuring air quality

Small amounts of carbon dioxide in the air are measured in part per million (PPM).

1PPM means that there is 1 gram of the pollutant substance in 1 million grams of air.

The other pollutant gases, carbon monoxide, nitrogen oxides and sulfur dioxide are measured in parts per billion (PPB).

The amount of pollutant gases are measured in air quality monitering stations throughout the UK. The data is transmitted automatically to a central computer for analysis.

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Correlation and cause

A correlation is a link between a factor and an outcome. Data is needed to show this.

To establish a casual link, evidence needs to show that changing a particular factor is the only cause of a particular outcome.

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Burning fuels

Oxygen is needed for any fuel to burn and release energy.

Fossil fuels such as petrol, diesel and fuel oil are mainly hydrocarbons. Hydrocarbons only contain carbon and hydrogen atoms.

Coal is a fossil fuel mainly made of carbon atoms.

Hydrocarbon fuel + Oxygen = Carbon + Water (+ energy)

Oxidation is when oxygen is added to a substance.

Reduction is when oxygen is removed from a substance.

Combustion (or burning) is an oxidation reaction.

Gases in the atmosphere can be separated.

Pure oxygen makes fuel burn more rapidly and at higher temperatures. One example is in an oxy-fuel welding torch, which can melt steel.

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Atoms in chemical reactions

Atoms do not change. In chemical reactions atoms get rearranged to make new substances.

Atoms of non-metal elements join to form molecules.

Elements are rearranged to make new compounds in chemical reactions.

Atoms in reactants are arranged into new products with different properties.

Mass is conserved in a reaction beause all the atoms in the reactants are just rearranged into the products.

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Burning sulfur

Solid yellow sulfur burns and makes a colourless gas called sulfur dioxide.

Sulfur is insoluble but sulfur dioxide dissolves in water and make an acid solution.

Fossil fuels contain small amounts of sulfur from the plants and animals that formed them.

When fossil fuels burn the sulfur burns:

Sulfur + Oxygen = Sulfur dioxide

Coal often contains the most sulfur, so burning coal an give off more sulfur dioxide than other fossil fuels.

In the 1970s people noticed forests and aquatic life in ponds were dying.

Scientists linked sulfur dioxide to acid rain.

Acid rain lowers the Ph of the land it lands on, harming living things or eroding carbonate rock.

Acid rain does not affect humans directly so it is an indirect pollutant.

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Forming pollutants

Power stations and transport make the most pollution because they burn the most fuel. Electricity prodution and transport has increased over the last century.

Sulfur dioxide is made by fuels containing sulfur. Carbon dioxide is allways formed when fuels burn.

If not enough air is availbale to burn the fuel:

  • Poisonous carbon monoxide is made.
  • Bits of solid carbon (soot) called particulates are made, making surfaces dirty.

Car engines make nitrogen oxides when nitrogen and oxygen In the air react at high temperatures, contributing to acid rain.

Air quality measurements need repeating many times because results vary. On dry, hot, calm days air pollutants can be trapped in cities.

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Forming pollutants

Carbon monoxide and particulate carbon are formed during incomplete combustion.

Only in the last 50 years have scientists discovered how different air pollutants form, and how they react with the air to produce smog, acid rain and climate change.

Nitrogen monoxide is formed in furnaces and engines at a temperature of about 1000 °C .

When nitrogen monoxide is released into the atmosphere it cools. It reacts with more oxygen to form toxic nitrogen dioxide.

Both nitrogen oxide and nitrogen dioxide pollutants can be in the air, so NOx is used to represent both of them.

NOx damages buildings, contributes to acid rain and can affect health.

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Complex reactions

Chemical formulae show how many atoms are joined together.

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Removing pollutants

Pollutants are removed from the air when:

  • Particulate Carbon settles on surfaces, making them dirty.
  • Sulfur and nitrogen oxides react with water and oxygen to produce a mixture of sulfuric acid and nitric acid in rain.
  • Carbon dioxide is used by plants for photosynthesis.
  • Carbon dioxide dissolves in rain water and in oceans.

Air quality an vary for several reasons.

Potential outliers could actually be valid data and removing them could lead to mistakes.

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Improving power stations

Burning oil and gas make less sulfur dioxide than burning coal.

Sulfur can be removed from oil and gas before it is burnt, but it is hard to remove from coal.

Power stations are developing ways of reducing pollution by cleaning waste gases.

They can remove solid particles using electrostatic filters.

Sulfur dioxide can be removed from waste gases by flu gas desulfurisation.

2 wet scrubbing methods used to remove sulfur from power stations are:

  1. Using an alkaline slurry of calcium oxide (lime) and water to make gypsum (calcium sulfate), which can be sold as plaster.
  2. Using sea water, a natural alkaline which absorbs sulfur dioxide.
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Reducing CO2

Ways of reducing our use of fossil fuels include: using alternative energy soures, improving building insulation, walking, cyling and using public transport.


'Carbon neutral' meaning when they are burnt they release the same amount of carbon dioxide as the plant used growing.

Large areas of land needed, which could be used for food.

Fossil fuels are not renewable so they are not a sustainable source of energy.

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Air pollution from transport

Air pollution from vehicles can be reduced by:

  • Using cars less
  • Using cleaner fuels and removing pollutants from exhausts
  • Making public transport cheaper, more frequent and in more places

Modern vehicles have more effiecient engines that use less fuels.

Catalytic converters contain a platinum catalyst that allow pollutant gases to react with each other.

Carbon monoxide + Nitrogen monoxide = Nitrogen + Carbon dioxide

Carbon monoxide gains oxygen so it is oxidised.

Nitrogen monoxide loses oxygen so it is reduced.

Low sulfur fuels are needed as sulfur damages the catalyst. This also reduces sulfur dioxide emissions.

Legal limits for exhaust emissions are enforced by MOT tests.

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Electric cars do not give out pollutants when being used, but the electricity being produced by burning fossil fuels does.

Few charging points are available at the moment.


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