The ozone layer is a fascinating and crucial topic for life on our planet. Its location, function, and problems have been the subject of numerous scientific studies and public debates in recent decades. Understanding its exact location, how it is distributed in the stratosphere, and the mechanisms that govern its formation and destruction is essential for protecting it and preserving environmental balance.
In this article, we offer a comprehensive guide written in a friendly, clear, and complete voice, so you can understand every aspect of the ozone layer: from its location in the atmosphere and its importance for life, to the challenges it faces, the causes of its deterioration, and the global actions implemented to restore it. Let's delve into all the secrets and curiosities of this invisible shield that protects us every day.
What is the ozone layer?
The ozone layer is an area of the Earth's atmosphere that contains a relatively high concentration of ozone molecules (O3), a gas composed of three oxygen atoms. This zone is not a homogeneous layer, nor is it "visible" to the human eye, but rather a region defined by its significant capacity to absorb ultraviolet (UV) radiation from the Sun. Without the presence of this atmospheric ozone, especially that in the stratosphere, life as we know it on Earth would be impossible; harmful UV radiation would flood the surface, radically increasing the risks of skin cancer, cataracts, and immune system damage, as well as severely damaging flora and fauna.
In quantitative terms, the ozone layer represents only a tiny fraction of the gases that make up the atmosphere. For example, in the area of maximum concentration, there are about 2-8 parts per million of ozone. If all the ozone present on Earth were compressed at standard sea level pressure and temperature, its thickness would be only about 3 millimeters. This gives a clear idea of how delicate and indispensable this gaseous layer is.
Location of the ozone layer in the atmosphere
To understand where the ozone layer is located, we must first briefly review the structure of the Earth's atmosphere, which is divided into several layers differentiated mainly by their temperature and composition: troposphere, stratosphere, mesosphere, thermosphere and exosphere.. The ozone layer is located almost exclusively in the stratosphere, located between 15 and 50 kilometers above the Earth's surface. However, the region where ozone concentration is highest is typically between 19 and 35 kilometers above sea level.
In the stratosphere, ozone accounts for approximately 90% of the total amount present in the entire atmosphere. This is because the conditions there, particularly the presence of intense ultraviolet radiation and the lack of pollutants, favor its formation and maintenance. Below this layer, in the troposphere (from the surface to about 10-15 km altitude), ozone also exists, but in smaller quantities and under different conditions.
The stratosphere and the ozonosphere
The stratosphere is the second layer of the atmosphere, located above the troposphere and extending from about 15 km to 50 km in altitude. In this layer, the temperature, instead of continuing to decrease with height as it does in the troposphere, begins to increase. This increase is a direct consequence of the absorption of UV radiation by ozone, which reheats this atmospheric layer.
The area of maximum ozone concentration within the stratosphere is called the ozonosphere. Although ozone is distributed at different altitudes, the ozonosphere is where the greatest absorption of ultraviolet radiation occurs. For this reason, the ozone layer and the ozonosphere are often used interchangeably, although technically the ozonosphere is a part of the stratosphere.
How is the ozone layer formed?
The process of ozone formation in the stratosphere is a fascinating interplay of light and molecules, resulting from the interaction between solar ultraviolet radiation and atmospheric oxygen. The mechanism that explains its production and destruction was first described by scientist Sidney Chapman in 1930 and is known as the "Chapman cycle."
It all starts when high-energy ultraviolet radiation (UV-C, with a wavelength less than 240 nm) hits oxygen molecules (O2), splitting each into two independent oxygen atoms. These highly reactive oxygen atoms bind almost immediately to other O molecules.2, forming ozone (O3). Thus, the Sun is not only responsible for the destruction but also for the generation of this natural defense of our planet.
The reaction can be outlined as follows:
- Dissociation of oxygen: O2 + UV radiation → O + O
- Ozone formation: O + o2 → Y3
The process is continuous and dynamic, with ozone formation and destruction occurring constantly. When ozone absorbs UV light (mainly UV-B and some UV-C), it decomposes back into O2 I. This maintains a balance between formation and destruction, which is essential for the layer to act as a filter without becoming excessively dense.
The point of maximum ozone generation is in the stratosphere above the equator, where the incidence of solar radiation is greatest. Stratospheric winds then distribute the ozone molecules to higher latitudes, such as the poles.
Distribution of the ozone layer: is it homogeneous?
The ozone layer is neither uniform nor static; its thickness and concentration can vary widely depending on latitude, altitude, season, and even from one day to the next. Generally, most ozone originates in areas near the equator, but the highest concentrations are usually recorded in the high latitudes of the northern and southern hemispheres, especially over Siberia and the Canadian Arctic.
Around the equator, the amount of ozone is lower because, although a lot of it is produced, it is also destroyed more quickly by the intense action of UV radiation. Therefore, it is common to find the lowest amounts of ozone around the equatorial belt and the highest values near the poles.
Ozone values in the atmosphere are usually expressed in Dobson Units (DU), which is the thickness that a given amount of ozone would have if it were compressed to one atmosphere of pressure and 0°C. For example, a compressed ozone column of 300 DU would be equivalent to a 3 millimeter sheet of pure ozone.
Functions and benefits of the ozone layer for life
The role that the ozone layer plays in protecting life is absolutely essential. Its main function is to absorb between 97 and 99% of the high-frequency ultraviolet radiation coming from the Sun (specifically the UV-C and UV-B bands), preventing it from reaching the Earth's surface directly. This natural filter protects all living beings and ecosystems. Without the ozone layer, UV radiation would cause a dramatic increase in diseases such as skin cancer, cataracts, and a general weakening of the immune system in humans and animals, and would severely disrupt plant life and aquatic ecosystems.
Another important function of stratospheric ozone is the control of atmospheric temperature. By absorbing ultraviolet radiation, ozone reheats the stratosphere, establishing a thermal gradient essential for global atmospheric dynamics. Without this warming, weather patterns and wind circulation would change radically.
Other layers: Ozone in the troposphere
In addition to stratospheric ozone, there is also ozone in the troposphere, the layer of the atmosphere that extends from the surface to about 10-15 km above sea level. However, here ozone is considered a polluting gas, harmful to health and the environment. It is known as "bad ozone"because it does not help filter harmful solar radiation, but is toxic at high concentrations.
Tropospheric ozone is not found naturally in large quantities, but is generated from photochemical reactions between primary pollutants. Gases such as nitrogen oxides (NOx), volatile organic compounds (VOCs), methane (CH4) and carbon monoxide (CO) released by traffic, industry and human activities react under the action of sunlight generating ozone.
Ozone in the troposphere is the primary cause of photochemical smog and is a greenhouse gas; it can cause respiratory problems and damage to crops and vegetation.
Ozone Layer Measurement: Dobson Units and Controls
The amount of ozone in the atmosphere is not measured in liters, cubic meters, or grams, but in Dobson Units (DU), named after the British scientist Gordon Dobson. One DU is equivalent to a 0,01 mm layer of pure ozone under normal pressure and temperature conditions. The global average ozone concentration is typically around 300 DU, although it can vary depending on altitude, latitude, and season. Values range from 200 to 500 DU in different regions of the world.
These measurements have been made for decades using spectrophotometers, balloons with sounding waves (ozonesondes), and satellites. For a better understanding of the importance of ozone in protecting the planet, see the article onbenefits offered by the ozone layer.
The destruction of the ozone layer: causes and consequences
Since the end of the 20th century, the ozone layer has faced a serious threat due to the emission of certain man-made chemicals, especially chlorofluorocarbons (CFCs) and other halogenated compounds. These compounds, widely used in refrigeration, air conditioning, aerosols, plastic foams, and cleaning products, are characterized by being inert in the troposphere and having a long atmospheric persistence.
Over the decades, CFCs and their derivatives slowly rise to the stratosphere, where, upon receiving ultraviolet radiation, they break down and release chlorine and bromine atoms. These highly reactive atoms initiate a chain reaction that catalytically destroys ozone molecules, meaning they can destroy countless ozone molecules before being inactivated or neutralized.
The result is an imbalance in the natural cycle of ozone formation and destruction, tipping the balance towards reducing the total amount of this gas in the stratosphere. This is how the phenomenon known as the "ozone hole" occurred, especially visible in Antarctica, where the seasonal decrease has led to the loss of up to 50% of stratospheric ozone during some months of the year.
The hole in the ozone layer: causes and peculiarities
The term “ozone hole” refers to the temporary and dramatic decrease in ozone levels over the polar region, especially Antarctica, during the southern hemisphere winter and spring. This phenomenon was identified in the 80s and triggered alarms worldwide.
The peculiarities of the Antarctic ozone hole are related to the extreme cold conditions in the stratosphere, where temperatures drop below -78°C, favoring the formation of stratospheric polar clouds. On the surface of these clouds, chlorine and bromine compounds from CFCs and halons undergo chemical reactions that transform them into highly reactive forms. When sunlight returns in spring after the polar winter, these compounds react with the ozone, destroying it at a rapid rate.
The ozone hole is more pronounced and recurrent at the South Pole, since stratospheric temperatures there are lower than those at the North Pole. However, similar phenomena, although on a smaller scale, have also been observed in Arctic latitudes during some particularly cold winters.
Effects of ozone destruction
The depletion of the ozone layer leaves the Earth's surface less protected against ultraviolet radiation, with risks to health and the environment. The main associated problems are:
- Increased incidence of skin cancers, cataracts, and immune disorders in humans.
- Changes in marine ecosystems: decrease in oceanic phytoplankton, the basis of the food chain.
- Losses in terrestrial vegetation, changes in flowering cycles and crop growth.
- Impacts on fauna, both terrestrial and marine, with long-term consequences for biodiversity.
Furthermore, the depletion of the ozone layer can indirectly contribute to climate change, since some of the substitutes for CFCs, such as hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs), have greenhouse effects..
Global actions to protect the ozone layer
The first major international agreement to protect the ozone layer was the Montreal Protocol, signed in 1987 and ratified by nearly every country in the world. To better understand global action on this issue, see the article on the legacy of Mario Molina.
The Montreal Protocol's success is notable for having halted and reversed the trend of ozone loss in the atmosphere, although the recovery process is slow due to the long persistence of these compounds in the atmosphere (some can last up to 200 years).
Subsequent amendments have also been promoted, such as the Kigali Amendment (2016), which seeks to reduce the use of HFCs, potent but non-ozone-damaging greenhouse gases. To learn more about the implications of these agreements, you can visit the article on .
Recovery and future of the ozone layer
Since the end of the 20th century, international controls have allowed ozone levels to stabilize and begin to recover in many areas of the planet. To learn about specific progress in this process, see the article onrecovery of the ozone layer.
Models and measurements indicate that, if current policies continue, the ozone layer could return to its pre-1980 levels around 2075, although this timeframe may vary depending on future emissions and climate change.
The recovery is particularly evident in the reduction in the extent and duration of the Antarctic ozone hole, although seasonal fluctuations continue to occur.
However, ongoing monitoring and reduction of human-caused pollutants remain essential.
What can we do to protect the ozone layer?
Protecting the ozone layer depends on collective action and the individual decisions we make every day. Some recommendations include:
- Buy products that indicate on their labels that they are free of CFCs and ozone-depleting substances.
- Avoid using fire extinguishers and aerosols containing halons, CFCs, and prohibited substances.
- Give preference to refrigerators, freezers, and air conditioning equipment that use ozone-friendly alternative gases.
- Reduce car use and opt for sustainable means of transportation.
- Promote environmental education to raise awareness about the importance of protecting the ozone layer.
Curiosities and facts about ozone and its measurement
Ozone was discovered in 1840 by Christian Friedrich Schönbein, who identified its characteristic odor during thunderstorms. Years later, in 1913, French physicists Charles Fabry and Henri Buisson discovered the stratospheric ozone layer by analyzing the absorption of solar radiation.
Ozone has a peculiar chemistry: it is highly reactive and, although considered essential in the stratosphere, can be dangerous at the Earth's surface.
Modern measurements, using devices such as Dobson spectrophotometers and ozone probes, have made it possible to determine with great accuracy the vertical and horizontal distribution of ozone in the atmosphere.
The relationship between ozone and climate change
Ozone, in addition to its role as an ultraviolet radiation filter, is also a greenhouse gas, capable of absorbing and emitting infrared radiation. In the stratosphere, its main function is to warm that layer and protect us from UV rays. In the troposphere, however, it contributes to global warming and negatively affects air quality.
Furthermore, many CFC substitutes, such as HFCs, while not ozone-depleting, do contribute to global warming.
This dual role means that protecting the ozone layer and combating climate change must go hand in hand, promoting alternative technologies that are safe for both challenges.
Associated phenomena: polar stratospheric clouds and atmospheric dynamics
During polar winters, special clouds known as polar stratospheric clouds form in the stratosphere, made of ice and nitric acid. These clouds provide the necessary surface area for chemical reactions that release reactive chlorine and bromine, accelerating ozone destruction when sunlight returns in the spring.
Atmospheric circulation, especially stratospheric winds, It is key to the transport of ozone molecules from its area of greatest production (the equator) towards mid and polar latitudes. Changes in atmospheric dynamics, whether due to natural or anthropogenic causes, can significantly influence the distribution and recovery of ozone.
The future of ozone research
Ozone science continues to evolve to understand all the factors that affect its distribution, recovery, and relationship to the global climate. New satellites and predictive models improve our ability to anticipate potential emerging threats, such as the emergence of new chemical compounds or the impact of climate change.
Constant monitoring and international cooperation are essential to ensure the success of ozone layer protection policies.
The ozone layer, although thin and seemingly fragile, is one of our planet's greatest natural treasures. Over the past few decades, we have learned to appreciate its importance and take measures to prevent its destruction. The combination of citizen awareness, global policies, and technological innovation will allow us to move toward a safer and more sustainable future, protecting life on Earth under this truly invisible blue shield.
