Stratospheric Ozone Depletion

Stratospheric Ozone

In the stratosphere, it forms a layer that absorbs ultraviolet radiation, which protects life on Earth.

Earth needed enough oxygen, which

developed around 2 billion years ago.

Ozone appears in both the stratosphere and the troposphere.

Once this layer formed, life could evolve outside

of the oceans!

Know Your UV ABCs!• UVA - penetrates deeper into skin

and causes immediate tanning.• Leads to premature aging of

the skin and enhances development of skin cancer.

A stands for aging!

• UVB - stronger than A, but cannot penetrate as deeply.• Responsible for burns, tans,

and skin cancer. B stands for burning!

• UVC - strongest and most dangerous.UVC and UVB are absorbed by the Ozone Layer!

How Does It Do It’s Job?

They reform to be able to break apart

once again!

The ozone molecules in the stratosphere absorb the sun’s UV light and break apart!

Every time a molecule of ozone is destroyed by the sun’s UV light, heat released, which is why there is a thermal

inversion in the stratosphere.

Stratospheric Ozone Depletion

Allows more UVB light to reach Earth’s surface, causing increased rates of skin cancer and cataracts.

CFCs, HCFCs, CCl4, methylchloroform, and halons (brominated flurorocarbons)

Ozone Depleting Substances (ODS)

A thinning of the ozone layer as a result of chemical reactions in the stratosphere.

Very stable, nontoxic, and environmentally safe in the troposphereContain chlorine and bromineHave a long life span

How Does it Work?

One CFC molecule can lead to the destruction of 100,000 ozone molecules.

Where does this Happen?The thinning of the ozone layer was discovered over the poles.

The ice promotes the collection of chlorine in the form of Cl2 gas.When the sun returns after the winter, the UV light breaks the Cl2

apart and the free chlorine atoms destroys the ozone.

Montreal Protocol of 1987International agreement to reduce and then

stop using ODS.

If We Can’t Use CFCS, Then What Can We Use?

HFCs have a very high global warming potential.

Hydrofluorocarbons are now used in refrigerators and air conditioning systems!

They do NOT deplete ozone!

But they are greenhouse gases!

How Are We Doing??The phase out of most ODS were complete in

between 2010 and 2015.

Did it work?

Are things Better?

Let’s Complete Activity 7 to find out!!

Please use the version posted in Canvas!

How Do They Compare?

Because the CFCs are so persistent, it takes longer to regenerate!

Rate of RegenerationTo calculate the rate of regeneration, we need to look at

the change in ozone concentration over time.

1994

Change in Concentration = 141.8 - 92.3 DU

92.3 Dobson Units

2017 141.8 Dobson Units

Change in Time = 2017 - 1994

Rate = 2.15 DU/year

How Old Will You Be?The ozone layer will be back to normal when it reaches

225 Dobson Units

2017

Change in Concentration = 225 - 141.8 DU

141.8 Dobson Units

? 225 Dobson Units

Rate = 2.15 DU/year

Time = (83.2 DU)/2.15 DU/year = 38.7 years!17 + 39 = 56! It should happen in your lifetime!

Or Will It??

An international agreement only works if everyone commits to it!