Chemistry of the atmosphere

Name all the gases in the atmosphere of the earth today

Nitrogen - 78%

Oxygen - 21%

other gases - small proportions (e.g. CO₂ water vapour and noble gases such as argon and methane

How long have the gases in the atmosphere today been around for?

The gases in the atmosphere have stayed pretty constant for around 200 million years

How old is the Earth and what does this mean?

The Earth is around 4600 million years old and that means that scientists cannot be certain about the early atmosphere.

What do scientists belive happend during the first billion years on Earth?

There was intese volcanic activity which released the gases that formed the atmosphere. One of these being water vapour.

What happend to the water vapour as the earth cooled?

The water vapour condensed to form the oceans

What did the Earth’s early atmosphere consist of?

In the early stages, the earth’s atmosphere consisted of mainly Carbon dioxide with little or no oxygen. This is due to the volcanic activity which released tonns of CO₂ into the atmosphere.

What other planets did the Earth’s early atmosphere look like now?

Mars and Venus today

What other gas other than CO₂ and water vapour were released by the volcanoes?

Nitrogen which gradually built up and small amounts of methane and ammonia

What are the differences between the Earth’s early atmosphere and the Earths atmosphere today?

Early = little nitrogen, contained large amounts of CO₂ , very little oxygen

Today = mainly nitrogen, contained small amounts of CO₂ , today 21% of the atmosphere is oxygen.

What happened to the CO₂ when the oceans were formed?

some of the carbon dioxide dissolved in the oceans to form a weak acid. This reacted with minerals in the sea to form precipitates. Over time, this formed sediments of carbonate rock on the sea bed. Some of the CO₂ in the sea was used to make corals and shells of organisms such as mussels. When these died, they formed the sedimentary rock limestone. This also removed carbon dioxide from the atmosphere. They is why the CO₂ began to decrease.

Where did the oxygen in today’s atmosphere come from?

Around 2.7 billion years ago photosynthetic algae first evolved in the oceans. Photosynthesis produced oxygen which entered the atmosphere. Over the following billion years, plants evolved. This increased the amount of oxygen in the atmosphere. At some point, the level of oxygen reached the point where animals could evolve.

What gas did photosynthesis reduce?

CO₂. The carbon can then be trapped in fossil fuels and again that caused the level of carbon dioxide in the atmosphere to fall.

What are fossil fuels?

Coal, oil and gas

What happens to some of the carbon which is used in photosynthesis?

Turns into fossil fuel

How long do fossil fuels take to form?

Fossil fuels are formed over millions of years.

Are fossil fuels renewable or non-renewable?

Non-renewable - if we keep using them, they will run out

How is coal formed?

Coal is formed from the remains of ferns and trees. If these die in marshy wetlands then they do not decompose. This can be due to a lack of oxygen or acidic conditions. These both prevent bacteria from carrying out secomposition. Over time, the plant remains are covered with sediments and compressed. The high temperature and pressure creates coal.

How is crude oil formed?

Crude oil is formed from plankton which are tiny plants and animals found in the sea. When these die, they settle in mud on the sea-bed. If oxygen is not present then they do not decompose. Over time, they are compressed by sediments. Heat and pressure then convert them into crude oil.

How is natural gas formed?

Natural gas is mainly the hydrocarbon methane. It is often found near deposits of oil this is because they are formed from plankton in a similar way to oil.

What do all fossil fuels contain?

Trapped carbon. This carbon was part of the carbon dioxide taken in by photosynthesis

Name 3 greenhouse gases?

Water vapour, carbon dioxide and methane

Describe what is meant by the greenhouse effect in terms of short wavelength radiation?

Energy from the sun travels to the Earth as short wavelength radiation e.g. UV and visible light. Some of the short wavelength radiation simply reflects back into space but most of it passes easily through the atmosphere. This is because short wavelength radiation does not interact strongly with the gas molecules in the atmosphere. The energy of the radiation is absorbed when it reaches the surface of the earth. The surface of earth now radiates the energy as long wavelength radiation such as infra-red.

Describe what is meant by the greenhouse effect in terms of long wavelength radiation?

Some of the long wavelength radiation interacts with the greenhouse gas molecules in the atmosphere. The energy in the long wavelength radiation is absorbed, because the energy is trapped in the atmosphere, this causes the temperature of the atmosphere to increase.

Advantages to the greenhouse effect?

The greenhouse effect keeps the temperature on Earth warm enough to support life.

What would happen if the greenhouse effect didn’t exists?

The earth would be too cold for most living organisms to survive.

What changes the level of water vapour

The level of water vapour varies widely so It depends on the temperature of the air.

Why are the CO₂ and methane levels increasing

Due to human activity

How is CO₂ increasing?

CO₂ is increasing as we burn fossil fuels. e.g. burning coal for electricity, burning petrol and diesel to power cars, burning gas to heat our homes.

The destruction on rainforests = deforestation.

How is CO₂ normally absobed?

by growing trees e.g. those in tropical rainforests.

How are rainforests destroyed and why?

In many cases, the forests are simply burned to provide land for grazing cattle. Burning forests again release large amounts of CO₂.

How is methane released?

In agriculture e.g. growing rice in flooded paddy fields. Methane is also released when cattle such as cows pass wind.

What is happening to CO₂ levels and methane and what does this mean?

They are both increasing. This means the temperature of the atmosphere is rising as more of the enegy from the sun is trapped.

What does rising temperatures mean?

Rising temperatures will increase melting of the polar ice sheets and glaciers. This will lead to increased sea levels. Increased sea levels could lead to more flooding of low-lying areas.

What could climate change lead to?

Lead to more severe weather e.g. more storms in the UK.

How does increasing temperaure effect animals.

Increasing temperatures could change the distribution of animals such as insects. It may even change the distribution of insect-borne diseases such as malaria.

What do many scientsits believe about climate change?

That is it caused by human activity causing the release of greenhouse gases.

What is peer-review and what does it allow for?

Is when evidence for climate change is shared between many different scientists. These scientists can then criticisse the evidence and decide whether it is valid. It allows scientists to detect false claims e.g. based on poor evidence or bias.

One probelm with understanding climate change

Climate change is complex and difficult to model so we sometimes see stories about climate change in the media that are simplified or simply biased. There is also speculation based on only parts of the evidence. This means that scientists must work harder to comminicate ideas around climate change to the general public.

What are some uncertainties about climate change?

We cannot predict with certainty how much the temperature of the atmosphere will increase. This can lead to speculation in the media.

What does carbon footprint tell us?

The carbon footprint tries to give us an idea of how much something contributes to climate change.

What is the carbon footprint?

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

How to reduce carbon dioxide emissions

A lot of energy is used to heat out homes. This often comes from burning fossil fuels. By insulating out homes or turning down the heating, we can reduce carbon dioxide emissions.

A great deal of carbon dioxide is released by driving cars. We can reduce this by using public transport such as buses and trains. These release less carbon dioxide per passenger.

A lot of carbon dioxide is produce by generating electricity by burning fossil fuels. We can reduce this by switching to renewable sources of electricity e.g. wind power.

How can we reduce the amount of energy we use at home?

Switch to energy-saving lightbulbs, turn appliances off at the plug rather than leaving them on standby.

Problems with reducing electricity?

Most of these solutions are expensive and people are reluctant to pay.

Sometimes they are inconvenient e.g. many people prefer to drive instead of using public transport.

How do we reduce methane emissions

One of the biggest sources of methane is agriculture. Grazing cattle such as cows release methane when they pass wind. One way to reduce that is for people to eat less beef and less dairy products.

Another source of methane are landfills. We can reduce this by trapping the methane and burning it to produce electricity. This is a good idea because methane is a much more powerful greenhouse gas than carbon dioxide, however, trapping and burning methane costs money.

Problem with trying to reduce methane levels?

People enjoy eating these and are unlikely to change their diets.

What are fuels?

Fuels release energy when they are combusted (burned)

two good examples of fuels?

Coal - often used to generate electricity in power stations and hydrocarbons - such as those found in petrol and diesel are used to power vehicles such as cars.

what do most fuels including both coal and hydrocarbons contain?

The elements carbon and hydrogen

What happens when we burn fuels?

When we burn fuels such as these, the carbon and hydrogen atoms react with oxygen in the air. These elements are oxidised.

Write the word equation for the combustion of methane?

methane + oxygen → carbon dioxide + water

Where is methane found and how is it usually used?

Methane is found in natural gas and is often used to heat homes

Chemical equation for the combustion of methane?

CH₄ + 2O₂ → CO₂ + 2H₂O

What happens to the carbon and hydrogen atoms in methane molecules during the combustion of methane?

The carbon atom in the methane molecule has been oxidised to form the gas carbon dioxide. The hydrogen atoms have been oxidesed to form water vapour.

How do do know that the combustion of methane is complete combustion?

We have made carbon dioxide, for complete combustion to happen, we need plently of oxygen. Carbon dioxide is a greenhouse gas, When humans burn fuels and relase carbon dioxide, this contributes to climate change.

What happens during the combustion of methane is oxygen is reduced?

If the amount of oxygen is reduced, then we make carbon monoxide instead of carbon dioxide.

What is carbon monoxide?

Is a toxic gas and it has no colour and no smell. This is why many people have carbon monoxide detectors in their homes.

what are three products of combustion

carbon dioxide, water vapour, carbon monoxide.

What do some fuels such as coal contain?

The element sulfur

What happens when coal is burned?

The sulfur atoms are oxidised (react with oxygen). This produces the gas sulfur dioxide.

How are oxides of nitrogen produced?

Inside engines, e..g in cars. This is when high temperatures cause nitrogen and oxygen from the air to react.

What is the products of the reaction between nitrogen and oxygen?

This produces a range of different molecules so scientsist call them all oxides of nitrogen (NO_x)

Issues with sulfur dioxide and oxides of nitrogen?

Cause breathing probelms in humans. They also dissolve in rainwater to form acid rain.

What can acid rain do?

Acid rain can damage trees and corrode bulding made from limestone.

One more pollutant made from burning fuels

When a truck burns diesel the particels of black smoke are released. These are particles of carbon (soot) and unburned hydrocarbons. This type of pollution is called particulates.

Issues with particulaties?

Particluates can damage human health e.g. they increase the risk of heart disease and lung disease. They can also reduce the amount of energy from the sun that reaches the earth’s surface. This is called global dimming

Potential problems with global dimming?

possibly affecting rainfall patterns