OZONE LAYER AND INFLUENCE OF COVID-19

Ozone layer, which is also known as ozonosphere can be found in the lower portion of the stratosphere that is 15-35 km above from the Earth. This layer consists of higher concentration of ozone. 90% of ozone in atmosphere presents in the stratosphere and it is referred as the ozone layer [1]. The thickness of the layer varies seasonally and geographically. As an example, ozone layer is thin near the poles. Ozone layer absorbs most of the ultra violet rays (UV rays) including 97-99% [2] of Sun’s medium frequency UV light. In addition, the layer absorbs solar radiations of wave lengths less than 290 nm and some other harmful forms of radiation. Due to the absorption of the solar radiation by the ozone layer, the temperature of the stratosphere is significantly high.   

Figure 01: The position of ozone layer in the atmosphere [3]

The ozone layer was discovered by the French scientists Charles Fabry and Henri Buisson in 1913.

Production of ozone in stratosphere

At the lower portion of stratosphere, chemical bonds of the oxygen molecules (O₂) break due to high energy solar photons. This phenomenon cause to occur single oxygen atoms.

O₂ + UV => O + O

Then these single atoms combine with remaining oxygen molecules and form ozone (O₃).

O+ O₂ => O₃

Most of the ozone in the stratosphere formed where the solar radiation level is high (equatorial belt).

Depletion of ozone layer

Now, the depletion of the ozone layer is becoming a global problem. It is due to the emission of manufactured chemicals mainly CFC gases (Chlorofluorocarbon) and halons. This problem was firstly described in a paper published by a Dutch Chemist Paul Crutzen in 1969. In his researches it was shown that the depletion was done by nitrogen oxides. Later in 1974, American chemists Mario Molina and F. Sherwood Rowland discovered that the ozone layer is mainly depleted by CFC [4]. CFC and halon cause chemical reactions to break the ozone molecules. It causes to reduce the solar radiation absorbing capacity of ozone layer. CFC is mainly released by the applications such as air-conditioning, refrigeration, blowing agents in foams etc. Halons released by the applications such as combustion.

Figure 02: Ozone depletion process [5]

The high emission of those ozone depleting substances by human cause to occur holes in the ozone layer. For the past few decades, the chemical reaction with the involvement of Chlorine and Bromine, cause the ozone layer deplete rapidly. Ozone depletion is greatly happened in South Pole. This depleted area is known as the ozone hole. This ozone hole was occurred in the spring over Antarctica.

Figure 03: ozone hole [6]

This ozone hole was grown for years. Though the maximum size of the ozone hole is decreasing as shown in the figure below.

Figure 04: Maximum ozone hole area [7]

Ozone depletion cause to have cancer risks (i.e.: skin cancer), eye damages (i.e.: permanent blindness, cataracts), sunburn, etc. [8]

How to protect ozone layer?

By avoiding the processes of emission of the manufactured gases such as CFC and halon, the ozone layer depletion can be reduced. As an example, minimizing the usage of motor vehicles reduce the halon percentage of atmosphere. Maintenance of air-conditioners properly or reducing the usage of air-conditioners can reduce the percentage of CFC in atmosphere. The global authorities (i.e.: The Montreal Protocol) also have taken some legal actions to protect ozone layer by banning the damaging chemicals [9]. And also, it was designated “September 16” as the international day for the preservation of the ozone layer.

Due to the lockdowns in most countries, for COVID-19, it has led to a significant reduction of air pollution due to the limited operation of industries as well as the motor vehicles. Nitrogen Dioxide dropped up to 60% in northern China, Western Europe and the U.S. in 2020 compared to 2019 [10]. And also, particulate matter pollution has gone down by 35% over northern China [10].  The reduction of the emission of CFC gases and halon in these days also likely protecting the ozone layer. Though, the reduction of air pollution due to lockdown is not the reason to close the ozone hole [11]. Main reasons are polar vortex, high-altitude currents that are responsible for bringing cold air to polar regions [11].

Polar vortex is a large area of low pressure and cold air surround the Earth poles. This effect is decreasing during summer season. Polar vortex is typically weaker in the Arctic region due to the presence of nearby land and the mountain ranges that disturb the weather. In this season, the ozone layer is healing mainly due to the unusual strong and long-lived polar vortex, and it is not mainly due to the air quality changes [12]

D.M.T.S. Rathnayake,

Faculty of Engineering,

University of Sri Jayewardenepura.

References

[1]	D. Wuebbles, "ozone layer, Atmosheric science," BRITANNICA, 17 April 2020. [Online]. Available: https://www.britannica.com/science/ozone-layer. [Accessed 14 May 2020].
[2]	B. Sparling, "The Ozone Layer," NASA Official, 30 May 2001. [Online]. Available: https://www.nas.nasa.gov/About/Education/Ozone/ozonelayer.html. [Accessed 14 May 2020].
[3]	"Biology Review of the Ozone Hole and Global Warming," School Tutoring Academy, 28 June 2015. [Online]. Available: https://schooltutoring.com/help/biology-review-of-the-ozone-hole-and-global-warming/. [Accessed 14 May 2020].
[4]	D. Wuebbles, "Ozone layer atmospheric science," BRITANNICA, 17 April 2020. [Online]. Available: https://www.britannica.com/science/ozone-layer. [Accessed 15 May 2020].
[5]	"What is Ozone Depletion?," eSchool Today, [Online]. Available: eschooltoday.com/ozone-depletion/what-is-ozone-depletion.html. [Accessed 14 May 2020].
[6]	E. Gray and T. Stein, "2019 Ozone Hole is the Smallest on Record Since Its Discovery," NASA TV, 21 October 2019. [Online]. Available: https://www.nasa.gov/feature/goddard/2019/2019-ozone-hole-is-the-smallest-on-record-since-its-discovery. [Accessed 14 May 2020].
[7]	EU, "Protection of the ozone layer," European Commission, [Online]. Available: https://ec.europa.eu/clima/policies/ozone_en. [Accessed 14 May 2020].