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The Ozone Layer - Part 1 | Environmental Chemistry | Chemistry | FuseSchool

in this video we will learn about the

two main layers of our atmosphere the

troposphere full of weather and bad

ozone and above that the stratosphere

we're good ozone protects us against

dangerous ultraviolet light our

atmosphere is made up of gases mostly

nitrogen and oxygen they're held to the

earth by gravity a sort of ocean of air

because air is compressible it gets less

and less dense as you get further from

the earth it's considered the first 50

kilometres where 99% of the atmosphere

is found visible sunlight passes through

the atmosphere and warms the ground

heating up the air at ground level as

the colder air above sinks it pushes up

the warmed air which is less dense due

to expansion this movement known as

convection current gives us our weather

systems the atmosphere gets colder and

colder till you reach about 10

kilometers the tropopause where the

temperature is coldest below this is the

troposphere containing 80 percent of our

air and all the weather above the

tropopause we have the stratosphere this

is a layer of thin air which is hot on

top because it's heated from above by

ultraviolet radiation absorbed by the

good ozone and cold underneath making it

dynamically stable contrast this with

the turbulent troposphere if you have

ever flown in a jet aeroplane you may

have had a bumpy ride after takeoff

through the turbulent troposphere but

once you're above the clouds above the

weather your journey is smooth Pella

planes cannot fly this high because the

air is too thin for the propeller to

grip the air so where does this good

stratospheric ozone come from pause the

video and think of the formula of ozone

well ozone is an allotrope of oxygen as

molecules are made of three oxygen atoms

bonded weakly together it is an unstable

gas which slowly decomposes back to

molecular oxygen the ozone in the

stratosphere is continually being made

and broken by the ultraviolet light in

the ozone oxygen cycle to start with UV

gets absorbed in the stratosphere by

molecular oxygen which splits into two

fast-moving atoms these fast-moving

oxygen atoms collide with air molecules

around them nitrogen and oxygen this

slows the free oxygen atoms down

enabling them to bond weakly with the

molecular oxygen to form ozone if

they're moving too fast they simply

bounce off the energy they shared with

the molecules in the air heats up the

upper atmosphere the oxygen atom has now

joined with an oxygen molecule to form

ozone ozone is very effective at

absorbing ultraviolet light which causes

the ozone to split back into an oxygen

atom and an oxygen molecule again

keeping the upper atmosphere warm ozone

reforms as before once the oxygen atom

is moving slowly again the ozone is

spread out through the stratosphere

shown here in black why do you think

there is so little ozone high up and low

down remember we need ultraviolet

radiation and oxygen to make ozone pause

and think

well here there is too little oxygen and

here near the tropopause a point of

lowest temperature where the troposphere

and the stratosphere join there is no

ultraviolet light available it has all

been absorbed by the ozone further out

so this is the ozone layer

if the ozone was squashed together like

a solid it would only be the thickness

of a sheet of cardboard but it is

actually a gas spread out over 20 or 30

kilometers before our atmosphere was

filled with oxygen the UV reached the

Earth's surface and prevented life from

emerging onto the land

ozone is also present in the troposphere

formed mainly by the action of sunlight

on pollution from motor vehicles here it

helps to form photochemical smog and is

a pollutant

you