The stratospheric ozone layer is Earth’s “sunscreen” – protecting living beings from too much ultraviolet radiation. But since the 1970’s, this layer is getting thinner and thinner which can lead to catastrophic effects. Ozone depletion, however, can be prevented and reversed when we work together.
Three is a powerful number
Ozone is pure oxygen, but whereas the oxygen molecules that we breathe in and that trees exhale are made of two oxygen atoms (O2), Ozone is made up of three oxygen atoms (O3). Ozone is constantly formed and destroyed in the lower layer of the stratosphere, which is about 9-18 miles (15-30 kilometers) high in the atmosphere. The formation of Ozone absorbs harmful UV-B radiation, which is high energy ultraviolet light. As UV-B radiation enters the ozone layer, O2 molecules become energized and split up in a reaction known as photolysis (greek, “light decomposition”). The newly single oxygen atoms will then react with other O2 molecules, forming an O3 molecule. The O3 molecule now stores the UV-B energy in its chemical bonds, and as more UV-B pours in from the sun, it causes those new strong bonds to vibrate, trapping the harmful radiation. The thickness of the ozone layer naturally varies throughout the year according to seasonal changes in UV radiation and atmospheric chemistry. These seasonal changes are most dramatic over Antarctica, where every spring the ozone layer becomes thinner than anywhere else in the atmosphere.
In the 1930s, chemicals called Chlorofluorocarbons (CFCs) were invented, which are highly stable compounds and excellent refrigerants. The refrigerants that people had been using prior to CFCs were highly toxic gasses such as ammonia (NH3), methyl chloride (CH2Cl), and Sulfur Dioxde (SO2). Unsurprisingly, before the advent of CFCs there were quite a few deaths caused by refrigerant leaks. CFCs were also popular for usage in aerosol products such as hair spray. In 1794, Mario Molina and Sherwood Rowland realized that since CFCs were so stable, that they could drift all the way up to the stratosphere without degrading. Once there, they would be bombarded with UV radiation, which would cause the chlorine atoms from their structures to break free. These free chlorine atoms would then attack the ozone, thereby decreasing the strength of the Earth’s natural sunscreen. In the 1980s scientists observed that the annual thinning of the ozone layer over Antarctica had become much thinner than what was natural or predicted. This dangerously thin layer of ozone is what is referred to as the ozone “hole.” CFCs were subsequently banned in 1987 by an international agreement known as the Montreal Protocol. Since then, nations have agreed to more stringent regulations on ozone depleting substances. There are still CFCs present in the atmosphere from the era before the Montreal Protocol was enacted – it will take many more decades before the ozone layer will be restored to its natural state.
How it affects us
Alright, so CFCs were banned… all better, right? Not exactly; it is evident that there is a long way to go before the ozone layer looks like how it did in 1979 (see video included). This means that an increased amount of UV-B radiation is able to impact life on this planet. Single-cellular microorganisms are particularly sensitive to UV-B radiation because they do not have a protective skin layer like animals do. This allows for the UV-B to directly impact their cellular organelles. Phytoplankton (greek, “plant drifters”) are photosynthetic microorganisms which could be threatened by increased UV-B exposure. This is a problem because they are basically the foundation for life as we know it, since they are responsible for producing at least 50% of the oxygen in the atmosphere. If that isn’t enough, increased UV-B exposure results in more cases of skin cancer in humans. It is not all bad news, as one study has estimated that by 2030, two million cases per year of skin cancer worldwide will be avoided as a result of the Montreal Protocol and its subsequent amendments.
CFCs were replaced with alternatives that are much less damaging to the ozone layer, which is a great success story and has resulted in the ozone hole starting to show the early signs of healing. The CFC alternatives are called Hydrochlrofluorocarbons (HCFCs) and Hydrofluorocarobns (HFCs), and unfortunately, they are not a perfect solution to the problem. The flaw of HCFCs and HFCs is that they are powerful greenhouse gases, leading to global warming, with anywhere between 700-12,500 times that of carbon dioxide.
The ozone hole may thankfully be one of the more straight-forward environmental problems that humankind has to deal with. The goal is to prevent additional emissions of ozone-depleting substances into the atmosphere. This will require continued cooperation among the nations of the world, and quick removal of any new chemicals that are discovered to negatively impact the ozone layer. Disappointingly, there seems to one or more nations that have decided it is alright to begin producing CFCs again, although no one knows exactly which one is doing it. Ozone requires a lot of energy to form, as it is formed by high energy solar radiation. Unfortunately, this means that using our technology to simply generate enough Ozone to account for the stratospheric deficiency is not feasible at this time.
There are climate-friendly refrigerants available, which do not have nearly the destructive effects of CFCs, HFCs, and HCFCs- Hydrocarbons (HC), such as propane and isobutene, are a prime example. The main drawback of HCs is their flammability. Simply supporting the implementation of natural refrigerants and/or refrigeration technology that supports their usage would be a step anyone can make to help the cause. Reading labels of aerosol and refrigerant products to check for CFC, HCFC, and HFC content can also help determine which of those products are safer for the environment. Last, but far from least, supporting government initiatives on climate change and ozone depletion is probably the greatest way that one can help, even if it doesn’t always feel like it.
article written by: Trent Pinion, Corpus Christi, Texas