C5.9. Chemistry of the Atmosphere

About 80% nitrogen, about 20% oxygen, and small proportions of carbon dioxide, water vapour and noble gases.

What is the approximate composition of the Earth's atmosphere today?

They have been much the same as they are today.

What were the proportions of gases in the atmosphere like for the last 200 million years?

It may have been mainly carbon dioxide with little or no oxygen, with some nitrogen and smaller amounts of methane and ammonia.

What was the Earth's early atmosphere probably like?

Intense volcanic activity released gases that formed the early atmosphere.

How was the Earth's early atmosphere formed?

It condensed to form the oceans.

What happened to water vapour released by early volcanoes?

Carbon dioxide dissolved in the oceans and carbonates were precipitated, forming sediments and reducing atmospheric carbon dioxide.

What happened to carbon dioxide when the oceans formed?

Volcanic activity released nitrogen, which gradually accumulated.

How did nitrogen build up in the early atmosphere?

Algae and plants produced oxygen through photosynthesis.

How did oxygen levels increase in the atmosphere?

About 2.7 billion years ago.

When did algae first produce significant amounts of oxygen?

Oxygen gradually increased, eventually reaching levels that allowed animals to evolve.

What happened to oxygen levels after algae began producing oxygen?

It decreased the percentage of carbon dioxide in the atmosphere.

How did photosynthesis affect atmospheric carbon dioxide?

Carbon dioxide was removed from the atmosphere and became locked into carbonate-containing sediments and rocks.

How did the formation of sedimentary rocks decrease atmospheric carbon dioxide?

Carbon became locked away in fossil fuels such as coal, crude oil and natural gas.

How did the formation of fossil fuels decrease atmospheric carbon dioxide?

Carbonates formed from dissolved carbon dioxide were deposited as sediments and eventually formed limestone.

How were deposits of limestone formed?

They formed from the remains of living organisms that were buried and subjected to conditions over very long periods of time.

How were coal, crude oil and natural gas formed?

Gases that absorb some of the infrared radiation emitted by the Earth and contribute to warming the atmosphere.

What are greenhouse gases?

Water vapour, carbon dioxide and methane.

What are the three greenhouse gases named in the specification?

They help maintain temperatures on Earth high enough to support life.

Why are greenhouse gases important?

The warming of the Earth's surface and atmosphere caused by greenhouse gases absorbing and re-emitting infrared radiation.

What is the greenhouse effect?

It passes through the atmosphere and reaches the Earth's surface.

What happens to incoming short-wavelength radiation from the Sun?

It warms and emits long-wavelength infrared radiation.

What happens when the Earth's surface absorbs radiation?

Greenhouse gases absorb it and re-emit it in all directions, including back towards Earth's surface.

What happens to some of the infrared radiation emitted by the Earth?

Greenhouse gases absorb and re-emit infrared radiation, transferring energy back towards the surface and lower atmosphere.

Why does the greenhouse effect warm the Earth?

Long-term changes in the Earth's climate, including changes in average temperature.

What is global climate change?

They believe human activities are causing the temperature of the Earth's atmosphere to increase at the surface, resulting in global climate change.

What do many scientists believe about human activity and global climate change?

The climate system is complex and contains many variables.

Why is it difficult to model global climate change?

Burning fossil fuels and deforestation.

What human activities increase carbon dioxide levels?

Farming, especially livestock farming, and decomposition of waste in landfill sites.

What human activities increase methane levels?

They release energy and can release carbon dioxide and other pollutants.

What happens when fossil fuels are burned?

A substance released into the environment that can cause harm.

What is a pollutant?

Carbon dioxide, water vapour, carbon monoxide, sulfur dioxide, oxides of nitrogen, particulates and unburned hydrocarbons.

What pollutants can be produced when fuels are burned?

By incomplete combustion of carbon-containing fuels.

How is carbon monoxide produced?

It is toxic and reduces the blood's ability to carry oxygen.

Why is carbon monoxide dangerous?

It is colourless and odourless.

Why is carbon monoxide difficult to detect?

Tiny solid particles, such as soot or carbon particles, suspended in the air.

What are particulates?

They can be produced by incomplete combustion of fuels.

How are particulates produced?

They can cause health problems and global dimming.

What are the effects of particulates?

A reduction in the amount of sunlight reaching the Earth's surface caused partly by atmospheric particulates.

What is global dimming?

By burning fuels containing sulfur.

How is sulfur dioxide produced?

It can cause respiratory problems and acid rain.

What problems are caused by sulfur dioxide?

They are produced when nitrogen and oxygen react at the high temperatures inside engines and other combustion processes.

How are oxides of nitrogen produced?

They can cause respiratory problems and acid rain.

What problems are caused by oxides of nitrogen?

Rain made more acidic by pollutants such as sulfur dioxide and oxides of nitrogen dissolving in atmospheric water.

What is acid rain?

It can damage plants, aquatic ecosystems, buildings and stonework.

What are the effects of acid rain?

Burning a fuel when there is insufficient oxygen.

What is incomplete combustion?

Carbon monoxide and carbon particles, as well as water.

What products can be formed by incomplete combustion of hydrocarbons?

Carbon dioxide and water.

What products are formed by complete combustion of a hydrocarbon?

Use the composition of the fuel and whether there is enough oxygen for complete combustion.

How can you predict the products of combustion?

Carbon dioxide is produced during complete combustion, while carbon monoxide can be produced during incomplete combustion and is toxic.

What is the difference between carbon dioxide and carbon monoxide?

Sulfur dioxide is produced and can react in the atmosphere to form acidic substances.

Why can burning fuels containing sulfur cause acid rain?

The high temperatures allow nitrogen and oxygen from the air to react.

Why can burning fuels in engines produce oxides of nitrogen?

Carbon monoxide is toxic, while sulfur dioxide, oxides of nitrogen and particulates can cause respiratory problems.

How can air pollutants affect human health?

They can reflect or scatter incoming sunlight, reducing the amount reaching Earth's surface.

Why can particulates cause global dimming?