The holes in the sky

We now know for sure that we are amid a climate crisis. So many different terminologies get thrown around, but do we know what any of them mean?

Let us take the ozone layer. We know that the ozone layer is somewhere up there and that there is a hole that is slowly starting to emerge through it, but does it have any real importance and how does it affect us? The simple answer is yes, it does affect us. However, this one-word answer does not do a great deal at helping us understand the significance of the issue.

The ozone layer, which sits around 20 km from the Earth’s surface, is an area with a high concentration of ozone molecules (which has the chemical formula of O3) in the stratosphere – the second major layer of Earth’s atmosphere between 12 to 50 km above the Earth’s surface. Although ozone is toxic to humans, in the stratosphere, it absorbs harmful ultraviolet radiation (UV-C and most UV-B radiation) from the Sun which protects us from genetic damage and possible cell mutations which can cause skin cancer. It also has the task of stabilising the Earth’s temperature.

 In the early 1970s, scientists have used satellites and ground stations to measure ozone levels and found evidence to show that human activities were disrupting the ozone layer’s natural cycle of being decomposed by ultraviolet radiation and then being formed again in natural processes. The production of chemicals such as chlorofluorocarbons (CFCs), an organic compound containing chlorine, carbon and fluorine atoms, has added factor that destroys ozone. CFCs have been made by humans, not derived from nature. In the past, CFCs were used widely as they are inert (do not react easily with other chemicals) and stable molecules. This makes them very useful in fire-safety equipment and as refrigerants.

CFC molecules can, however, be broken down by ultraviolet radiation. In the troposphere -the lowest level of the Earth’s atmosphere, CFCs are protected from UV radiation by the ozone layer and so move as a whole molecule. This is where the problem starts to occur. Once the CFCs enter the stratosphere, the CFC molecules are not protected from UV radiation by the ozone layer but break down using the energy from the UV radiation from the Sun and release chlorine atoms. These chlorine atoms then react with ozone molecules (O3), taking one oxygen atom to form chlorine monoxide, ClO and an oxygen molecule, O2.

However, when a chlorine monoxide molecule meets an oxygen atom, the oxygen atom breaks up the chlorine monoxide, taking the oxygen atom and releasing the chlorine atom back into the stratosphere to react with, and destroying more ozone.

This reaction happens repeatedly, allowing a single atom of chlorine to eliminate ozone molecules forming ‘holes’. (These are not literal holes but areas where there have been significant depletion in the levels of ozone)

Fortunately, chlorine atoms do not remain in the stratosphere forever. When a chlorine atom reacts with gases such as methane (CH4), it forms hydrogen chloride (HCl), which can be carried down from the stratosphere into the troposphere, where it can be removed from the air by dissolving in the rain forming acid rain.

According to World Atlas, scientists now have images showing the ozone is recovering with a 20% decrease in ozone depletion between 2005 and 2016. In 2019, the smallest ozone hole since 1982 was recorded over Antarctica. However, in 2020 the largest hole ever observed was found over the Arctic and took longer to close due to atmospheric conditions.

So, the ozone is destroyed as part of its role of protecting us from harmful radiation from the Sun but damaging emissions are speeding up this natural process meaning that the ozone is being destroyed faster than it can repair itself. If humans stop putting CFCs and other ozone-destroying chemicals into the stratosphere, the ozone layer could eventually repair itself and therefore potentially bring the Earth’s temperature back to normal and eliminate the climate crisis.

Demi Bako

2 thoughts on “The holes in the sky

  1. Some very interesting and excellent chemistry. It is worth remembering that the main concern for CFC’s is their ozone depletion in a radical catalytic cycle. Also other radicals such as bromine, hydroxyl and nitrogen monoxide radicals cause similar ozone depletion upsetting the balance between ozone depletion and formation. Although CFC’s do absorb in the critical window between carbon dioxide and water IR absorption bands. The amount present is so much smaller than that of carbon dioxide that carbon dioxide remains the most worrying of the greenhouse gases and increases in levels in the atmosphere will continue to be a major cause of global warming. An excellent blog.

    Liked by 1 person

    1. Thank you Verity.
      It is very interesting to see that CFCs are not the only chemicals disrupting the balance between ozone depletion and formation and it is important for the world as a whole to quickly look for ways to reduce carbon dioxide emissions.

      Liked by 1 person

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