Did you know that, little by little, the ozone layer is thickening? If you want to refresh your general knowledge about the ozone layer, please continue reading this page. If you want to learn only about the healing of the ozone layer, please go directly to page two. If you just want to see some beautiful planetary maps of the ozone layer, please go straight to page three.
The ozone layer is the Earth’s natural sunscreen
The ozone layer or ozone shield is a region of Earth’s stratosphere that absorbs most of ultraviolet (UV) radiation coming from the Sun. The ozone layer contains a high concentration of ozone (O3) – close to 10 parts per million – comparative with other parts of the atmosphere, where the average concentration is about 0.3 parts per million. The ozone layer is mainly found in the lower portion of the stratosphere, from approximately 15 km to 35 km above Earth. Its thickness varies worldwide and is generally thinner near the equator and thicker near the poles.
Although the concentration of the ozone in the ozone layer is very small, it is vitally important to life because it prevents the ultraviolet light (UV) coming from the Sun to reach the Earth’s surface. Extremely short frequency ultraviolet radiation (10–100nm) is screened out by nitrogen (N). The UV radiation capable of penetrating nitrogen is divided based on its wavelength into three categories: UV-A, UV-B, and UV-C, which are described in Table 1.
| UV-A (315-400nm) | Ozone is transparent to most UV-A, a longer-wavelength UV radiation, so the majority of it reaches the Earth’s surface. UV-A is significantly less harmful to DNA, although it may still potentially cause physical damage, premature aging of the skin, indirect genetic damage, and skin cancer. |
| UV-B (280-315nm) | UV-B radiation can be harmful to the skin and is the main cause of sunburn. Excessive exposure can also cause cataracts, immune system suppression, and genetic damage, resulting in problems such as skin cancer. The ozone layer is very effective at screening out UV-B. Nevertheless, some UV-B, particularly at its longest wavelengths, reaches the surface, and is important for the skin’s production of vitamin D in mammals. |
| UV-C (100-280nm) | UV-C is very harmful to all living things. Fortunately, it is entirely screened out by a combination of O2 (< 200nm) and O3 (> 200nm) by around 35 km altitude. |
Table 1: Types of UV radiation
A number of free radical catalysts, including nitric oxide (NO), nitrous oxide (N2O), hydroxyl (OH), atomic chlorine (Cl), and atomic bromine (Br), have a destructive effect on the ozone layer. In 1976, atmospheric research revealed that the ozone layer was being depleted by some chemicals released by the industry, especially chlorofluorocarbons (CFCs) and bromofluorocarbons (BFCs). These are highly stable gases capable to rise unchanged to the stratosphere, where Cl and Br radicals are then liberated by the action of UV light.
Ozone levels have dropped by a worldwide average of about 4% since the late 1970s. For approximately 5% of the Earth’s surface, around the North and South Poles, much larger seasonal declines have been observed. The most dramatic ozone loss is above the South Pole, where an “ozone hole” appears every spring (see Figure 1). An “ozone hole” is not actually a hole, but an area of damage in the ozone layer in which the ozone is thinner.
The ozone map for the Southern Pole from September 2019 (this is when the spring begins in the Southern Hemisphere) shows quite a bit of improvement, even though the worldwide economy was up and running at its full potential. That improvement seems to have evaporated in 2020-2022, despite the fact that during the pandemic the worldwide economy slowed down considerably.
I did not find any explanation for this fact. If you are aware of such an explanation, please post it in the Comments section.