Kate O’Brien

Global Warming

atmosphere

Infrared radiation

Solar radiation

atmosphere

Solar radiation

Most radiation in absorbed by earth’s surface & warms it

Some radiation is reflected by the Atomsphere & Earth’s surface

atmosphereInfrared radiation

Infrared radiation is emitted from the Earth’s Surface

Some radiation passes through the atmosphere , and some is absorbed and re-emitted (which warms the Earth)

This is called the Greenhouse Effect

Greenhouse gases

Methane (CH4)

Carbon Dioxide (CO2)

Water (H2O)Skip

Carbon Dioxide (CO2)CO2 in atmosphereco

mbu

stio

n

Respiration

photosynthesis

decay

The concentration of CO2 is dependant on:

The addition of CO2 by:

• Volcanic eruptions

• Respiration (plants and animals)

• Burning + Decay (plants)

(and addition by the oxidation of hydrocarbons – ie MethaneMethane!)

The removal of CO2 by:

• Photosynthesis (green plants)

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Back to greenhouse gases

Methane (CH4)

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Although there is less methane than carbon dioxide in the atmosphere, it contributes to the greenhouse effect more

It is added to the atmosphere by:

• The production of coal, gas and oil

• From rotting organic waste

• From Cows’ digestion

(and trapped in ice-like structures below the northern sea, If this was released it would have a huge impact on the greenhouse effect)

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Water (H2O)

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Addition from evaporation from lakes and oceans

By far the most abundant greenhouse gas

When Carbon Dioxide: O=C=O, absorbs infrared radiation, it vibrates.Eventually, this vibration will cause the molecule to emit its own energy (radiation) - this can then be absorbed by another greenhouse gas or by Earth’s surface

In CH4, the C-H bonds absorb infrared radiation

In H2O, the O-H bonds absorb infrared radiation

How do gases absorb radiation?

The greenhouse effect of a gas is dependant on both its concentration and its ability to absorb infrared radiation

Scientists use this vibration to measure the levels of pollutants in the atmosphere

• 47% of the energy which enters the atmosphere reaches Earth’s surface

It is the portion of re-emitted energy which keeps the Earth’s surface at 14˚CWithout this re-emitted infrared energy, it would be -20˚C to -40˚C.

This is the greenhouse effect

The greenhouse effect creates an equilibrium between the energy emitted, and the energy being absorbed.

This balance is being disturbed by emissions to the atmosphere. There is concern that the rising levels of carbon dioxide will lead to global warming

In the Arctic, ice is melting

In the Antarctic, ice sheet is melting into the oceans

Tropical areas are experiencing more storms and floods

In Europe there have been extreme heat waves

Between 1995 and 2006 we experienced some of the warmest years on record.

Rivers have overflowed due to excessive rainfall and melting glaciers

Drought and disease ruin harvests

Increasing temperatures expand ocean water, this contributes to rising sea levels

Earth Summit 1992– Kyoto Protocol

There was international agreement that dangerous climate change must be prevented

By 1997 100 signed up to be part of the Kyoto Protocol, and this committed countries to reduce their emissions by 5% by 2012

However, the USA refused to sign; and in 2006, 25% of global carbon dioxide emissions came from the USA

Whichever method is used, carbon emissions must be reduced by 70-80% to stabilise atmospheric concentration& to stop global warming

European Union Strategies Targets by 2020:

• At least 20% of energy to come from renewable sources

• At least 10% of transport fuels to be ‘biofuels’.

• Greenhouse gas emissions to be reduced by 20% below 1990 levels

In 2007 the UK published a draft ‘Climate Change Bill’Which aims to find a way to cut the UK emissions by 60% from 1990 by 2050(with a 26-32% decrease by 2020)

From this year (2012) cars must emit no more than 130g CO2 per km(it was 165g/km in 2005)

Solutions to the Greenhouse Effect

Alternative Fuels

Carbon capture and storage

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Alternative Fuels

Wind turbines

Tidal power

Solar panels

Nuclear PlantsBack to Solutions

This involves capturing carbon dioxide from power stations and storing it safely, instead of it being released into the atmosphere.

Carbon capture and storage

Underground, porous rock can act as a sponge to store CO2

Old oil + gas fields are some of the best natural places to store CO2

BP is developing the first project to create decarbonised fuels. This would see a reduction in CO2 emissions by 90%.

The present fuel is made through this reaction:

CH4 + 2O2 CO2 + 2H2O

In decarbonised fuel, water is used to produce CO2 + H2, where the CO2 is will be separated and piped offshore into oilfields nearing the end of their productive life, this also enables us to extract the final 30% of the oil, which is usually extremely difficult.

It is thought that there is about 10 years worth of space in oilfields, and a further 30 years in gas fields, and other porous rocks could hold up to 500 years of CO2

Back to Solutions

The Ozone LayerOzone is good when its found in the upper atmosphere

(stratosphere) – it protects us from harmful ultraviolet light from reaching the Earth.

Ozone is bad when it is near to Earth’s surface (troposphere) – it is an air pollutant with harmful effects on the respiratory system.

O3

troposphere

stratosphere

Ozone layer

The ozone layer is in the stratosphere, 10-50km above Earth.

The ozone layer filters out wavelengths shorter than 320nm which would be damaging to life, converting it into heat (which is why the ozone is hotter than other parts of the atmosphere).

Ozone layer

UV-a

5%absorbed

95%absorbed

100%absorbed

UV-b UV-c

Formation of OzoneAbsorption of UV radiation breaks an O2 molecule into two oxygen

atoms

O2 + (radiation < 240nm) –› 2O

These O atoms then react with oxygen molecules

O2 + O –› O3 + heat

This heat is absorbed by air molecules in the stratosphere, raising its temperature.

How the Ozone layer worksThe ozone molecules (O3) absorb UV of wavelengths 240-310nm. O3 molecules are

converted back to O2 molecules + O atoms

O3 + (radiation < 310nm) –› O2 + O

The O atom immediately reacts with the O2 to reform ozone

O2 + O –› O3 + heat

In this way the chemical energy release when O + O2 combine is converted into heat.

Overall, the UV radiation is converted into heat.

This cycle keeps the ozone layer in balance.

O2 + O –› O3 + heat

Removal of Ozone

O3 + O –› 2O2

Luckily, the natural removal process is quite slow, however human activity can affect the rate & balance of this.

Ozone Depletion – Cl radicals.Chlorine radicals in the stratosphere can disrupt the natural balance of ozone-oxygen.

Chlorine radicals mainly come from chlorofluorocarbons, CFC’s. CFC’s can only be broken down by the UV radiation found above the ozone layer.

CFC’s take a long time to reach the ozone layer, and once there, UV radiation provides the energy needed for this reaction, which damages the ozone, to happen.

Initiation

When UV radiation strikes a CFC molecule, a C-Cl bond breaks, forming a chlorine radical:

CFCl3 –› Cl• + •CFCL2

Propagation

This chlorine radical can react with an O3, break it apart + destroy the ozone.

Step 1: Cl• + O3 –› ClO• + O2

Step 2: ClO• + O –› Cl• + O2

Overall: O3 + O –› 2O2

These propagation steps repeat many times, so a single CFC molecule can destroy thousands of ozone molecules

Ozone Depletion – •NOAnother radical that destroys the ozone is nitrous oxide,

•NO from lightning or aircrafts.

This also proceeds with 2 propagation steps:

Step 1: •NO + O3 –› •NO2 + O2

Step 2: •NO2 + O –› •NO + O2

Overall the same reaction occurs:

O3 + O –› 2O2

The biggest source of nitrous oxides is the combustion of oil and petrol (and the combustion of coal).

Internal combustion engineTraffic emissions are one of the biggest contributors to air pollution. The internal combustion engine in cars emits

atmospheric pollutants:

Carbon monoxide (CO)

This is a poisonous gas emitted by incomplete combustion. It can exist in the atmosphere for a month before being oxidised to CO2.

Carbon monoxide is extremely bad for our heath: It reduces the amount of oxygen supplied to tissues and organs. This leads to carbon monoxide poisoning.

Nitrogen Oxides (NOx)

Nitrogen oxides are produced in a high-temperature process during the burning of fuels in the internal combustion engine. 2 oxides are produced:

1 Nitrogen monoxide: NO

2 Nitrogen Dioxide: NO2

Nitrogen dioxide forms low-level ozone and nitric acid (which contributes to acid rain).

They are also respiratory irritants and low levels affect asthmatics.

Unburnt Hydrocarbons

Two compounds are of concern: benzene and buta-1,3-diene as they are know to be human carcinogens.

Once released into the atmosphere, the unburnt hydrocarbons and nitrous dioxide react together to form low-level ozone (photochemical smog). For humans this causes serious medical problems, including breathing problems and susceptibility to infections

Catalytic ConverterThese have been fitted into all EU cars since 1993. It has a ‘honeycomb’ arrangement to give it a large surface area. (and it does its job, a typical one has a surface area as big as 2 football pitches!)

The exhaust gases pass over the catalytic surface & harmful gases are converted into less harmful products, which are released.

Oxidation Catalyst (for Diesel engines)3-Way Catalyst – Petrol Engines

2CO + O2 –› 2CO2

C12H26 + 18½O2 –› 12CO2 + 13H2O 2NO + CO2 –› N2 + CO2

Some of the CO or NO molecules are held onto the metal surface. Temporary bonds are formed between the gas molecules and catalytic surface, which is how the molecules react together. After the reaction, the CO2 and N2 are desorbed and diffuse away.

Infrared Spectroscopy