topic 9 - Chemistry of the Atmosphere

What is the composition of Earth's atmosphere today?

Approximately 78% nitrogen, 21% oxygen and about 1% other gases, including argon, carbon dioxide and water vapour.

What were the main gases in Earth's early atmosphere?

Mainly carbon dioxide, with little or no oxygen. There was also nitrogen and possibly small amounts of methane and ammonia.

How old is the Earth?

Approximately 4.6 billion years old.

How was Earth's early atmosphere formed?

Intense volcanic activity released gases, including carbon dioxide, water vapour and nitrogen, forming the early atmosphere.

Why is there uncertainty about the composition of Earth's early atmosphere?

The Earth formed billions of years ago, so there is limited direct evidence of the conditions and gases present.

How did the oceans form?

As the Earth cooled, water vapour in the atmosphere condensed to form liquid water, which collected in oceans.

How did the formation of oceans reduce carbon dioxide in the atmosphere?

Carbon dioxide dissolved in the oceans. It was then removed from the atmosphere as carbonates formed and became sedimentary rocks.

How did photosynthesis change Earth's atmosphere?

Algae and plants removed carbon dioxide and released oxygen, increasing atmospheric oxygen and decreasing carbon dioxide.

When did algae first produce oxygen?

Approximately 2.7 billion years ago.

Why did oxygen levels gradually increase over time?

Algae and later plants carried out photosynthesis, releasing oxygen into the atmosphere.

How did the percentage of carbon dioxide in the atmosphere decrease over time?

Carbon dioxide dissolved in the oceans, was used in photosynthesis, and became locked away in sedimentary rocks and fossil fuels.

How was limestone formed from carbon dioxide?

Carbon dioxide dissolved in the oceans, and carbonate compounds formed sediments that eventually became sedimentary rocks such as limestone.

How were coal, crude oil and natural gas formed?

They formed from the remains of ancient organisms buried under sediment and converted over millions of years by heat and pressure.

How was coal formed?

From ancient plant material buried in swamps and converted over millions of years by heat and pressure.

How were crude oil and natural gas formed?

From ancient organisms, mainly plankton, buried in sediment and converted by heat and pressure over millions of years.

What is a greenhouse gas?

A gas that absorbs some of the infrared radiation emitted by the Earth's surface, helping to keep the planet warm.

Name three greenhouse gases.

Water vapour, carbon dioxide and methane.

What is the natural greenhouse effect?

Short-wavelength radiation from the Sun reaches Earth. The surface absorbs energy and emits long-wavelength infrared radiation. Greenhouse gases absorb some of this infrared radiation and re-emit it in all directions, warming the atmosphere and surface.

What is short-wavelength radiation mainly associated with in the greenhouse effect?

Incoming radiation from the Sun.

What is long-wavelength radiation in the greenhouse effect?

Infrared radiation emitted by the warmed Earth's surface.

How do greenhouse gases warm the Earth?

They absorb outgoing infrared radiation and re-emit it in all directions, including back towards the Earth's surface.

Why is the natural greenhouse effect important?

It keeps Earth's average temperature warm enough to support life.

What is the enhanced greenhouse effect?

The increase in warming caused by rising concentrations of greenhouse gases due to human activities.

How do humans increase carbon dioxide levels in the atmosphere?

By burning fossil fuels and through deforestation.

How does burning fossil fuels increase atmospheric carbon dioxide?

Carbon in the fuel reacts with oxygen during combustion, producing carbon dioxide.

How does deforestation increase atmospheric carbon dioxide?

Fewer trees remove carbon dioxide by photosynthesis, and burning or decomposing felled trees can release stored carbon dioxide.

How do humans increase methane levels in the atmosphere?

Through cattle and other livestock, rice farming, and leaks from fossil fuel extraction and waste disposal.

How does cattle farming contribute to methane emissions?

Microorganisms in the digestive systems of cattle produce methane, which is released into the atmosphere.

How can landfill sites produce methane?

Microorganisms break down organic waste in anaerobic conditions, producing methane.

What is global warming?

The long-term increase in Earth's average surface temperature.

What is global climate change?

Long-term changes in global or regional climate patterns, including temperature, rainfall and extreme weather.

What is one possible effect of global climate change on sea levels?

Sea levels may rise because ice on land melts and warmer seawater expands.

How can climate change affect weather patterns?

It can change rainfall patterns and increase the likelihood or intensity of some extreme weather events.

How can climate change affect ecosystems?

Habitats may change or disappear, causing changes in species distribution and biodiversity.

How can climate change affect food production?

Changes in temperature and rainfall, droughts and floods can reduce crop yields in some regions.

Why can climate change have different effects in different regions?

Regions differ in their climate, geography, ecosystems, water availability and ability to adapt.

Why do scientists use climate models?

To use data and scientific understanding to predict possible future climate changes under different conditions.

Why are predictions of climate change uncertain?

The climate system is complex, and predictions depend on assumptions about future emissions and other variables. Models also have limitations.

Does uncertainty mean scientists have no evidence for human-caused climate change?

No. Multiple lines of evidence support human-caused climate change, although the exact scale and timing of some future effects remain uncertain.

Why is peer review important in climate science?

Other scientists assess the methods, evidence and conclusions before research is published, helping identify errors and improve reliability.

How can you evaluate a report about climate change in an exam?

Consider the quality and amount of evidence, whether the source is reliable, whether the work has been peer reviewed, whether alternative explanations are considered and whether uncertainty is acknowledged.

What is a carbon footprint?

The total amount of carbon dioxide and other greenhouse gases emitted over the full life cycle of a product, service or event.

What does the life cycle of a product include when calculating its carbon footprint?

The emissions associated with raw materials, manufacture, transport, use and disposal.

How can individuals reduce their carbon footprint?

Use less energy, improve home insulation, use public transport or walk and cycle where practical, reduce waste and choose lower-emission products.

How can businesses reduce their carbon footprint?

Improve energy efficiency, use lower-carbon energy, reduce waste and emissions during manufacture, and improve transport and supply chains.

How can governments help reduce carbon dioxide emissions?

Support renewable energy, improve public transport, set emissions policies and encourage energy efficiency.

How can methane emissions be reduced?

Reduce leaks from fossil fuel production, capture landfill gas, and use farming practices that reduce methane emissions.

Why might reducing greenhouse gas emissions be difficult?

It can be expensive, require new technology and infrastructure, affect jobs and industries, and require cooperation between countries.

Why is international cooperation important for climate change?

Greenhouse gases mix in the atmosphere, so emissions from one country affect the global climate.

What is an atmospheric pollutant?

A substance released into the air that causes harm to humans or the environment.

What are the main atmospheric pollutants produced by burning fuels?

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

How is carbon monoxide formed?

It forms during incomplete combustion of carbon-containing fuels when there is insufficient oxygen.

Why is carbon monoxide dangerous?

It is toxic, colourless and odourless, so it is difficult to detect. It reduces the blood's ability to carry oxygen.

What are particulates?

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

How is soot produced?

It can form during incomplete combustion of fuels containing carbon.

What are the effects of particulates on human health?

They can enter the respiratory system, worsen breathing problems and contribute to lung and cardiovascular disease.

What is global dimming?

A reduction in the amount of sunlight reaching the Earth's surface, partly caused by particulates reflecting or scattering sunlight.

How is sulfur dioxide produced during combustion?

Sulfur impurities in fuels react with oxygen to form sulfur dioxide.

What are the effects of sulfur dioxide?

It can cause respiratory problems and contribute to acid rain.

How are oxides of nitrogen formed in car engines?

At high temperatures, nitrogen and oxygen from the air react to form nitrogen oxides.

What are the effects of oxides of nitrogen?

They can cause respiratory problems and contribute to acid rain.

What is acid rain?

Rain made more acidic by pollutants such as sulfur dioxide and nitrogen oxides reacting in the atmosphere to form acids.

How can acid rain damage the environment?

It can damage trees and aquatic ecosystems and cause weathering of limestone buildings and statues.

What is complete combustion?

Combustion with enough oxygen, producing carbon dioxide and water when a hydrocarbon burns.

What is incomplete combustion?

Combustion with insufficient oxygen, which can produce carbon monoxide and/or carbon particulates as well as water.

Why can the same fuel produce different pollutants under different conditions?

The products depend on the fuel's composition and the amount of oxygen available during combustion.

Which pollutant is produced by sulfur impurities in fuels?

Sulfur dioxide.

Which pollutant is produced when carbon-containing fuels burn with insufficient oxygen?

Carbon monoxide and/or carbon particulates.

Which pollutants form when nitrogen and oxygen react at high temperatures in engines?

Oxides of nitrogen.

What is the difference between a greenhouse gas and an atmospheric pollutant?

Greenhouse gases absorb infrared radiation and contribute to warming. Atmospheric pollutants harm health or the environment; some substances can be both.

What is the difference between global warming and global dimming?

Global warming is an increase in Earth's average temperature. Global dimming is a reduction in sunlight reaching Earth's surface due partly to particulates.

Why is reducing air pollution important even if a pollutant is not a greenhouse gas?

It can still harm human health, damage ecosystems or cause acid rain.

What should a strong exam answer include when explaining how the atmosphere changed?

Identify the gas that increased or decreased, name the process responsible and explain how that process changed its concentration.

What should a strong exam answer include when explaining the greenhouse effect?

Mention incoming short-wavelength solar radiation, absorption by Earth's surface, outgoing long-wavelength infrared radiation, and absorption and re-emission by greenhouse gases.