ScienceBenefits and risks

Radiation that is not absorbed by the atmosphere reachesthe Earth's surface and warms it, leading to the greenhouseeffect. Some radiation, such as ultraviolet, exposes our skinto harmful rays and puts us at risk of developing skincancer.

The atmosphereSome radiation of the electromagneticspectrumelectromagnetic spectrum: The different types ofelectromagnetic radiation, arranged in order of frequency orwavelength. is absorbed by the atmosphere, but some istransmitted.

Light, some infrared, some ultravioletultraviolet radiation:Electromagnetic radiation with a frequency between that ofvisible light and X-rays., and microwavesmicrowaves:Electromagnetic radiation with a frequency between that ofvisible light and radio waves., pass through the atmosphere andreaches the Earth’s surface. Gamma raysgamma radiation:High frequency electromagnetic radiation emitted duringradioactive decay. Many centimetres of lead or metres ofconcrete are needed to absorb it., X-raysX-rays: High frequencyelectromagnetic radiation, used for medical imaging., most of theultraviolet and some of the infraredinfrared radiation:Electromagnetic radiation emitted from a hot object. areabsorbed by the atmosphere and do not reach the Earth’ssurface.

InfraredInfrared from the Sun reaches the Earth’s surface and warms it.

The warm Earth emits some infrared radiation, and some of thisis absorbed by gases in the atmosphere. This is called thegreenhouse effect. If there were no greenhouse effect, the Earthwould be too cold for life as we know it.

PhotosynthesisLight from the Sun reaching theEarth’s surface provides the energyfor plants to produce food byphotosynthesisphotosynthesis:The chemical change that occurs inthe leaves of green plants. It useslight energy to convert carbondioxide and water into glucose.Oxygen is produced as a by-product

Light from the sun reaching

earth

of photosynthesis..

Photosynthesis replaces carbon dioxide in the atmosphere withoxygen. This reverses the process of respiration.

MicrowavesThe atmosphere transmits

microwaves, and these

can be usedto communicate with satellites.

Radiation and cell damageAny radiation absorbed by living cells can damage them byheating them. However, ionising radiations are

more likely todamage living cells. This is because photons of ionising radiationdeliver much more energy. They can easily kill cells, and canalso

cause cancer by damaging the DNADNA: The materialinside the nucleus of cells, carrying genetic information. DNAstands for Deoxyribonucleic Acid. in the nucleus of a cell.

Effects of microwaves

Microwavesmicrowaves:Electromagnetic radiation with afrequency between that of visiblelight and radio waves. in theenvironment may be harmful, butthere is no agreement on this. Theyare not ionising, and so cannotcause cancer in the way thatultravioletultraviolet radiation: Electromagnetic radiation with afrequency between that of visible light and X-rays., X-raysX-rays: High frequency electromagnetic radiation, used for medicalimaging. or gamma raysgamma radiation: High frequencyelectromagnetic radiation emitted during radioactive decay.Many centimetres of lead or metres of concrete are needed toabsorb it. do.

Microwave ovens work because the food contains watermolecules which are made to vibrate by the microwaves. Thismeans that food absorbs microwaves and gets hot. Themicrowaves cannot escape from the oven, because the metalcase and the metal grid on the door reflect microwaves back intothe oven.

WatchYou may wish to viewthis BBC News itemabout campaignerswinning a two-yearbattle to get a mobilephone mast movedaway from a primaryschool.

Watch

Some people think that mobilephones, which transmit and receivemicrowaves, may be a health risk.This is not accepted by everyone, asthe intensity of

the microwaves is toolow to damage tissues by heating,and microwaves are not ionising.

Ultraviolet

One health risk which is definitelypresent in our environment isultraviolet, in sunlight. Not much ofthe ultraviolet reaching the Earthgets to us, because the ozone layerhigh up in the atmosphere absorbsmost of it. In the summer, it is wiseto use sun-screens and clothing to

Umbrellas can be useful in

the sun as well as the rain

absorb ultraviolet, and prevent itreaching the sensitive cells of the skin.

The ozone layer - higher only

The ozone layer absorbs ultravioletbecause ultraviolet

ionises theozone, which then changes tooxygen. This

chemical change isreversible, and the oxygen changesback to ozone.

Ideas about science - risk

Scientific or technologic

aldevelo

pments often introduce new Ozone

molecule formation

risks.

Chemicals used in aerosol spray cans and fridges, whenreleased into the atmosphere, gradually made their way upto the

ozone layer, and

removed some of it. This h

asincreased the intensity of the ultravioletradiationultraviolet radiation: Electromagnetic radiationwith a frequency between that of

visible light and

X-rays.reaching the Earth

. These chemicals are not used anymore, and the ozone layer is gradually returning to normal.

However, this will take a few years.

It is important to be able to assess the size of risk in any activity.No activity is completely safe.

The consequence of too much ultraviolet – skin cancer –often does not appear until much later in life, so it doesn'tseem a real risk to young people.It is difficult to assess how much ultraviolet you arereceiving when you are sunbathing. If you feel hot, that isbecause of the infrared, not the ultraviolet.Weather forecasts now inform you of the intensity ofultraviolet radiation. See for example BBC weather.

BenefitsFor most risky activities, there are benefits as well as risks:

sunbathing produces a sun tan, which many people findmore attractivesome ultraviolet is good for you, as it produces vitamin Din the skin

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Making a judgement - higher onlyTo make a judgement about a possible bad outcome you needto consider two factors:

What is the chance of the outcome happening?What is the consequence of that outcome?

The precautionary principleThe ‘precautionary principle’ tells you to avoid any activity ifserious harm could arise.

Parents may insist that their children are not allowed out

on the beach at all in the summer months.

The real risk may be very different from the perceived risk iethe risk that you think is there.

You can’t see ultraviolet, and the word ‘radiation’ soundsfrightening to many people. This makes the risk seemworse than something you can see, and which is morefamiliar.Some parents may assume that summers are no differentfrom when they were young, so there is no danger to theirchildren.Other parents may be very alarmed by stories of increasesin skin cancer, and not let their children out in sunnyweather at all. This is the precautionary principle.

The ALARA principleThe ALARA principle is to make any risk As Low As ReasonablyAchievable. This usually applies to an organisation which isresponsible for its employees.

a company employing lifeguards on the beach may insistthat they wear lycra sun-suits and sun-screen cream toabsorb ultraviolet when they are on dutythe company may also arrange that lifeguards take turnsat covering the hottest part of the day, when the intensityof ultraviolet is greatest

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