Stratospheric Ozone

Did you know that we have 2 ozone layers? One of them is in the stratosphere and the other one in the troposphere. Let’s start with the one farther: the stratospheric ozone layer. 

This layer is important to the evolution of life on Earth and continued health and survival of life. Stratospheric ozone is the layer that we have been worried about because of the depletion that caused by anthropogenic factors such as chlorofluorocarbons (CFCs) and natural factors such as melting of ice crystals in the atmosphere at the beginning of the Antarctic spring. Then what will happen if the stratospheric ozone decreases? Well, the UV rays that reach the Earth’s surface will increase. Exposure to UV can lead to skin cancer and cataracts in humans. 

There are 3 different types of UV rays: UVA, UVB and UVC.  

• UVC: Almost 100% absorbed by oxygen and ozone in the atmosphere  

• UVB: About 90–95% absorbed by the ozone layer (UVB radiation is particularly harmful because it can damage DNA in living organisms.) 

• UVA: About 95% reaches Earth’s surface (only weakly absorbed) 

What is Antarctic Spring? 

You might be imagining a colder April or May maybe, but Antarctic Spring isn’t something like that unfortunately. Starting off, Antarctica is located in the southern hemisphere which makes spring September, October and November. The Antarctic winter can create polar stratospheric clouds full of ice crystals, and these crystals melt in the beginning of the spring when the sunlight returns. The chemical reactions convert less reactive chlorine into a more reactive form. Then, chlorine degrades ozone into atmospheric oxygen (O₂).  This process thins the ozone layer naturally.  

Chlorofluorocarbons (CFCs) 

As the difficulty and length of its name, the harm it has inflicted on the world is great. It is a propellant used as a refrigerant.  When the CFCs escape, they enter the stratosphere and destroy the ozone layer.  

Overall, the ozone (o₃) reacts to form oxygen causing the ozone depletion. As stated in the Antarctic Spring, chlorine is the atom causing it. When we look at the reactions of CFCs’ single chlorine atom can destroy thousands of ozone molecules through a catalytic cycle. Because the chlorine atom is regenerated at the end of the reaction, ozone depletion continues even after CFC emissions are reduced. It will take decades for CFC’s currently in stratosphere to completely dissipate, allowing the ozone layer to fully repair. Since the CFCs are persistent, they were replaced with hydrofluorocarbon (HFCs), a greenhouse gas without chlorine to enter the cycle. The use of CFCs was phased out under the Montreal Protocol. While they were replaced with Hydrofluorocarbons (HFCs) to save the ozone layer, HFCs were later found to be potent greenhouse gases, leading to further international agreements to phase them out as well. 

The naturally occurring stratospheric ozone layer was affected by anthropogenic and natural factors. However, the effect of depletion has a much wider range. This depletion leads to the disruption of terrestrial and marine photosynthesis, particularly affecting phytoplankton, which forms the base of the marine food web . When the primary producers are affected, the food chains and population of organisms get afflicted. The UV lights passing through can create genetic problems such as cancer and mutation. The situation is even more serious for organisms sensitive to UV rays. For example, when the shell-less, membrane-bound eggs of amphibians are exposed to UV rays in water, they may mutate inside and never hatch, or they may be born with defects, which could spell the end for amphibians.  

In conclusion, what has been done cannot be undone, but plans can be made for the future of the Earth. Minimizing CFC use was a start; many more steps will be taken in the future to reduce the ozone hole to its smallest possible size.