Most of us be it in high school or elementary school, must have heard about the ozone layer. And how it acts as a protective blanket that shields us from UV-radiations. Now, you’re going to be reading about it again but this time, it is about the possibility of the layer healing itself. And hopefully dissuade our concerns about the numerous dangers posed by the sun rays because of the compromised layer.
Where is the Ozone Layer
To some non-science geeks, the ozone layer may sound abstract and seem like it doesn’t exist, just a sort of science gibberish. Well, I’m here to tell you that it actually does.
But where is it?
The ozone layer is actually located in the lower portion of the stratosphere. Now, the stratosphere is a layer of the earth’s atmosphere that’s just above the troposphere. The troposphere is the layer closest to the earth’s surface and basically a host to our weather (rain, cloud and snow). Scientists have discovered that most of the ozone, i.e about 90% on earth, is concentrated in the stratosphere.
You may be wondering how much of it is present. It has been calculated to be in the parts-per-million units. 1 ppm is so minute and could be simply understood as 32 seconds out of a year! The stratosphere is known to contain 2-8 ppm of ozone. This is due to the temperature changes that occur in this region.
What’s the Rave about the Ozone Layer?
A lot of reports and studies have been done on the stratospheric ozone layer. In fact, policies have been put in place to protect it from further damage.
Why is this so? What is so special about this ozone?
Well in the later part of the 19th century, some scientists discovered that some wavelengths of UV-light were blocked by a molecule in the stratosphere. This molecule turned out to be ozone. The UV-radiations were later found to cause skin cancers and increase skin aging, damage human DNA, and cause a number of other harmful effects to humans and plants. You see, if ozone was completely absent, the amount of UV-radiations earth received, would have decimated most life on it. This is why we should be concerned about the substances that could reduce the production of stratospheric ozone and take action into regulating their usage.
The Ozone-oxygen cycle
So far, we’ve been talking about ozone and its usefulness to life. But right now, we will take time to know how it is formed and its involvement in reducing the amount of UV-light reaching us. The mechanism by which this happens is best illustrated with the ozone-oxygen cycle.
When sun rays reach the earth, it splits molecular oxygen, O2, into 2 atomic oxygen, 2O. A single atomic oxygen then goes on to react with O2 to form ozone (a triatomic oxygen). It is from here that the real work begins. Ozone then react with the UV-radiations to be splitted again into O2 and O. This ozone-oxygen cycle ensures continued production of ozone in the atmosphere. But some other compounds have been found to interrupt this process when they react with oxygen. Thereby, potentially causing damage to life by hampering ozone production.
Should We be worried about these Ultraviolet Radiations?
On the electromagnetic spectrum, there is a division of radiations – ionizing and non-ionizing – into the left and right hand side. To the right are the ionizing radiations while the left has the non-ionizing radiations. The ionizing radiations have high frequencies and are able to knock off electrons from atoms in water, air and living tissues. This makes them extremely harmful and require protective gears by humans when in use. Examples are x-rays and gamma rays.
On the other hand, non-ionizing radiations have low frequencies and are unable to knock off electrons. They are only capable of heating substances. An example is microwaves used in food preservation. This is also the category that the ultraviolet radiations falls in on the EM-spectrum. The sun emits 3 major UV-radiations on the earth: UV-C, UV-B and UV-A. Apart from the sun, UV rays are also found in tanning beds, black lights and electric arc lighting. So for those of us that tan the artificial way, this could be harmful to you.
Absorption of UV-radiation
Studies have shown that UV absorption occurs the most at peak sunlight and at shorter wavelengths. UV-C, also called short-wave UV, is the radiation that is completely absorbed by ozone before it even reaches the earth’s surface. UV-B, the most harmful radiation, is mostly absorbed but not completely, requiring the invention of sunscreens to lessen its effects. Conversely, UV-A, because of its longer wavelength – between 310-400 nm – is not absorbed by ozone. It accounts for 95% of the sun’s UV rays. UV-A was previously thought to pose less danger to us but recent studies have linked its indirect involvement to the pathogenesis of skin cancer.
UV-B and UV-A (UV-C is completely absorbed by ozone) penetrate and damage the skin. The most dangerous UV light, UV-B directly damages DNA by reacting with the covalent bonds linking the nitrogenous bases. This consequently exposes adjacent pyrimidine bases (thymine) which go on to react with each other and form thymine dimers.
Thankfully, the DNA repair system takes care of this. But we all know that there’s no 100% efficient system. Some of the dimers escape this repair and go on to interfere with DNA replication, this causes mutation of cells. UV-A is quite harmless and causes tanning but it negatively affects DNA indirectly. It does this by creating free radicals, unstable compounds that steal electrons from biomolecules like DNA.
More importantly, melanin, a dark pigment in our skin, helps absorb some of these rays and release them as heat. Pale skinned persons become “tanned” while for dark skinned persons, they become darker.
The Greenhouse Effect
The concept of the greenhouse effect is tied with actual greenhouses. They are structures built with lightweight and transparent material to allow easy access for sunlight in order to trap heat. The aim is to create specific conditions for a particular crop to grow, either for commercial or domestic purposes. Greenhouses use convection as a means of trapping and transferring heat.
Convection is a form of heat transfer from a less dense, hotter material to a more dense colder material. This causes heat to be retained and circulated in a medium. But in reality, the greenhouse effect occurs when a planet is able to retain or trap heat after radiation from its planetary star reaches it. In this case, the earth and the sun.
Greenhouse Gases
The greenhouse effect is achieved by the presence of some gases in the atmosphere. They include water vapor, carbon(IV)oxide, methane, nitrogen oxide, ozone, chlorofluorocarbons (CFC) and hydrogenfluorocarbons. Carbon(IV)oxide has the highest concentration. Human industrial activities since the 17th century have greatly increased the concentration of CFCs and halocarbons in the atmosphere. These chemicals are used in aerosol sprays like insecticides, refrigerants, propellants, dry-cleaning and degreasing solvents, etc. They all have the tendency of depleting ozone levels.
In the late 1970s, studies showed that CFCs and halocarbons (carbon compounds containing halogens like bromine and fluorine) were harmful to the ozone layer. When CFCs and halocarbons react with UV radiation, free chlorine and bromine atoms are released. They later go on to react with oxygen, reducing ozone concentration. Also, Dutch chemist, Paul Crutzen gave accounts of nitrogen oxide being another cause of ozone depletion. The mechanisms by which this happens are the same with CFCs and halocarbons when in contact with UV-radiations.
Is The Ozone Layer Healing?
After its depletion was first noticed in 1979, there has been considerable increase in the size of the ozone column, i.e ozone hole. Sadly, the ozone layer at the Antarctic zone has shown significant decrease over the years. The largest ozone hole was recorded to be 28.4million km2 (this is about 5 times the size of the EU) in September 2000. It wasn’t until 2019 there were positive reports about the ozone hole. The United Nations Environment Program (UNEP) Montreal Protocol is a policy heavily focused on climate change. It has helped in the reduction of ozone-depleting substances (ODS) usages since 1986.
The Road to Recovery
On a brighter note, numerous environmental organisations, climate-change activists and international governments have helped in advocating and enforcing policies to preserve ozone. Among others are reducing carbon footprints in the form of minimizing fossil fuel burning and the use of electric cars. Also, the regulation of ODS have gone a long way to create positive impacts on climate change. All these have yielded considerable results because recently, reports have been given about the likelihood of the ozone hole closing up by the 2060s.
Although, some scientists warn of an incomplete recovery due to the difference in temperature and atmospheric conditions from decades before. We can only hope that from the change seen in 2019, while strictly complying with reducing the consumption of ODS, the possibility of the ozone column closing up is within reach.
But the journey to such destination is still posed with lots of challenges. Because for one, ozone is a greenhouse gas that also contributes to global warming. Hence our efforts in retaining it will also have negative impacts on climate change thereby creating a paradox. Also, there is no outright ban on the use of CFCs, meaning the actual time it’ll take for the ozone column to heal may be longer.
Conclusion
The growing concern on climate change is well founded on the fact that seasons and temperatures known to specific regions have changed. Since earth is ever evolving, the fear that it is doing so at a much faster pace and to our detriment is enough reason to be thorough with how safe industrial activities are. Ozone is an important chemical for all life on earth. Our collective efforts to preserve it will go a long way into prolonging life on earth and also reduce health care costs that arise from the complications of UV exposures.
Sources
NCEH >> UV radiation.www.cdc.gov. Retrieved 06 February 2023.
UV Radiation & Your Skin. www.skincancer.org. Retrieved 06 February 2023.
What is the current state of the ozone layer?www.eea.europa.eu. Retrieved 06 February 2023.
ozone depletion.www.britanica.com. Retrieved 06 February 2023.
Burren, R., Scaletta, C., Frenk, E., Panizzon, RG., Applegate, LA. (1998). “Sunlight and carcinogenesis: expression of p53 and pyrimidine dimers in human skin following UVA I, UVA I + II and solar simulating radiations”. Int J Cancer 76:201–206.
