International Day for the Preservation of the Ozone Layer

By Larry Ger Aragon/Philippines
Edited by Cecilia Razafinirinamaharavo/Madagascar

Graphics by Javan Lev Poblador/ATO-ClimatEducate Project

​September 16 marks one of the special dates for the environment – the International Day for the Preservation of the ozone layer. This day commemorates the date of signing of the 1987 Montreal Protocol on Substances that deplete the ozone layer, an environmental treaty by the United Nations in controlling the consumption and production of ozone-depleting substances and is considered as one of the most successful environmental treaties in history.

But what exactly is ozone layer in the first place? What does it protect us from? And why should we care about it?

Figure 1. The electromagnetic radiation (EM) spectrum with emphasis on the ultraviolet (UV) wavelength range.
Source: https://www.uvfab.com/wp-content/uploads/2019/01/UVspectrum1.jpg

1. Our sun emits more than the visible light

​​​The sun radiates different wavelengths across the electromagnetic (EM) spectrum, most of which are invisible to our naked eyes (see figure 1). Many living organisms on our planet benefit from visible to longer wavelengths in the EM spectrum, while wavelengths shorter than the visible range harms us upon prolonged exposures. Luckily, the earth’s atmosphere filters out most of the harmful wavelengths before it reaches the ground, except for some part of the ultraviolet (UV) rays (see figure 2).

Figure 2: Penetration of different wavelengths across the EM spectrum
​Source: https://imagine.gsfc.nasa.gov/Images/science/EM_spectrum_atmosphere.jpg

2. Ultraviolet rays are harmful on us

​Ever wonder why lotions often have sun protection factors (SPF) labels? These products shield us from the UV rays, the shorter wavelengths just before the visible range (see figure 1). This UV radiation has three categories, namely UV-C (100-280 nm), UV-B (280-315 nm) and UV-A (315-400 nm). We can just skip UV-C as it gets absorbed right away in the upper atmosphere. We focus on the effects of longer UV wavelengths, the UV-A and UV-B, which in essence does more harm than good. The World Health Organization (WHO) states that while UV-A promotes vitamin D formation in the skin, prolonged exposure to it can cause redness and premature skin aging. UV-B on the other hand, can harm us more with sunburn, damages to the DNA, cataracts, and possible skin cancer1. While our atmosphere cannot block most of the UV-A from reaching the surface, it can absorb most of the UV-B in the stratosphere through the region called ozone layer.

Figure 3: Absorption of different UV rays in the layers of the atmosphere including the stratospheric ozone layer.
Source: http://www.theozonehole.com/images/uvrayjp.gif

3. Our ozone layer shields us from these harmful UV rays

​Ozone (chemical formula O3) is a very reactive and colourless gas which is dominantly found in the stratosphere. Coined from the Greek word ozein which means “to smell”, this compound is known for its peculiar odour as described by C.F. Schönbein who first discovered it in mid-18th century2. The stratospheric ozone protects the earth’s surface from UV rays by photolyzing particularly the UV-B range (see figure 3). A thicker and healthier ozone layer in the stratosphere therefore promotes stronger shield from these harmful UV radiation.

4. However, we emit compounds that destroy the stratospheric ozone layer

​Emissions of human-made chemicals have depleted the ozone layer over the last few decades. It was found in the 1970s that halogen-containing compounds are able to seed catalytic destruction of stratospheric ozone particularly over the Antarctic region3. Halogen compounds such as chlorofluorocarbons (CFCs) and bromine halocarbons found in aerosol spray cans, refrigerators, and other commercial agents remain chemically stable in the ground for decades to centuries and only photolyze in the stratosphere by reacting with ozone compounds. Every percent (1%) loss in stratospheric ozone from these reactions creates ozone hole that allows harmful UV-B to reach the surface by two percent (2%)

5. UN established a treaty that recovers ozone hole

​The 1987 Montreal Protocol has prevented further depletion of stratospheric ozone layer and increases in surface UV-B rays5. Halogen-containing compounds in the stratosphere have fairly reduced since the late 1990s, allowing the springtime total column ozone in Antartica to slowly recover based on its 2001 to 2013 concentration levels. The Montreal Protocol has also maintained the negligible to small ozone depletion over the tropics and mid-latitudes.

This global movement proves that we can still fix the environmental damage we have done to keep our planet habitable. The Montreal Protocol preaches a success story about harmonizing science, policy and global activism which we hope to also pull off as we face more complex environmental problems such as climate change.

References
1 World Health Organization. Ultraviolet Radiation. Available online at https://www.who.int/uv/faq/uvhealtfac/en/
2 Schönbein, C. F. (1840). On the odour accompanying electricity and on the probability of its dependence on the presence of a new substance. Philosophical magazine, 17, 293-294.
3 Molina, M. J. & Rowland, F. S. (1974). Stratospheric sink for chlorofluoromethanes: Chlorine atom catalysed destruction of ozone. Nature, 249, 810-812.
4 Seinfeld J. H., Pandis S. N., 2006. Atmospheric Ozone. In Atmospheric Chemistry and Physics, 2nd edition. 52-55. John Wiley & Sons, Inc, Hoboken, New Jersey.
5 Mäder, J. A. et al. (2010). Evidence for the effectiveness of the Montreal Protocol to protect the ozone layer. Atmospheric Chemistry and Physics, 10, 12161-12171.
6 World Meteorological Organization (WMO), 2018. Executive Summary: Scientific Assessment of Ozone Depletion: 2018, World Meteorological Organization, Global Ozone Research and Monitoring Project - Report No. 58, 67pp., Geneva, Switzerland.
Seinfel and Pandis.

THE AUTHOR

Larry Ger Aragon is one of the new Science and Solutions Advisers in ClimatEducate from the Philippines. He has a bachelors degree in Meteorology and is now finishing his masters in Atmospheric Science. Aside from research works, he joins the country's Department of Science and Technology in promoting different fields of Science to younger students through its Science Explorer program. For most of his rest time, he is either sleeping, binge-watching random asian series and animes, or singing songs with high notes that he cannot even reach, pretty much the basic errands a normal person would do.