What is the ozone layer and what does it do?

Recent Met Office forecasts for UV are indicating low to moderate levels, however there is a possibility that the levels may in fact be much higher than this today.

Scientists say high UV levels are due to changes in the ozone layer.

So what exactly is the Ozone?

Ozone is a gas which is an allotrope (or form) of oxygen which occurs naturally in the earth atmosphere.

The form of oxygen we are most familiar with is di-oxygen, O2. It constitutes 21% of the earth’s atmosphere.

Ozone is tri-oxygen, or O3. It is much rarer, typically averaging 3 molecules in 10 million.

Where is Ozone?

Only 10% of ozone occurs in the layer of the atmosphere closest to the earth’s surface. Although naturally occurring, levels are raised significantly by pollution.

Here it is mostly regarded as ‘bad’ ozone – leading to the formation of smog and potentially causing irritation damage to life on earth.

This is not the part of the atmosphere we are concerned with in this instance.

The stratosphere is home to 90% of atmospheric ozone. It is here that we find the ‘ozone layer’. Here ozone acts as ‘good ozone’, acting as a vital screen to the earth from damaging ultraviolet (UV) radiation from the sun.

The Ozone layer do?

Ultraviolet from the sun is classified as three types, based on the wavelength of the radiation – UV-a, UV-b and UV-c.

Ozone molecules react with the different wavelengths of UV to different extents.

A strong interaction with UV-c means it is entirely screened out at around 20 miles up.

Ozone has little effect on UV-a, but this radiation does not cause sunburn or direct genetic damage so is not the form of greatest concern. UV-b is the wavelength known to have the greatest impact on life on earth, with overexposure directly linked to DNA damage such as skin cancer. Fortunately ozone is able to screen out the majority of UV-b, but some still reaches the earth’s surface.

Any decreases in the thickness of the ozone layer will obviously result in increased levels of UV-b reaching the earth’s surface.

Source: BBC

N.H.Khider