Causes of Ozone Layer Depletion: Human-Made and Natural Causes

In the Earth’s atmosphere, there is a significant depletion of the ozone layer. The ozone layer protects us from harmful ultraviolet rays from the sun. Human activities and some natural processes thin the ozone layer. Several chemicals, including CFCs, HCFCs, and halons, negatively affect the ozone layer. Here, we’ll explore the main causes of ozone layer depletion.

Introduction: Ozone Layer

The Earth’s atmosphere is composed of different layers. The troposphere is the lowest layer of Earth’s atmosphere where all human activities happen.

The next layer in Earth’s atmosphere is the stratosphere. Most of the atmospheric ozone also concentrates on the lower layer of the stratosphere. Ozone contains three oxygen molecules. These ozone molecules create an ozone layer in the stratosphere. The ozone layer absorbs radiation from the sun and prevents it from reaching the Earth’s surface. In short, the ozone layer absorbs the harmful ultraviolet radiation from the sun that may cause various adverse effects on living organisms on the planet Earth.

The ozone layer acts as a protective shield that protects us from hazardous UV radiation. Unfortunately, this protective shield is depleting due to various reasons; most of which are human-made ones. Natural causes are there too, but the impact is less than human-made reasons. Several factors contribute to ozone layer depletion, but first, let’s understand what ozone depletion is.

What Is Ozone Depletion?

In simple terms, the reduction of the ozone concentration in the stratosphere is known as ozone layer depletion. The primary substance that disturbs the ozone concentration is CFCs i.e., chlorofluorocarbon. The depletion of the ozone layer starts when CFCs enter into the stratosphere layer of Earth’s atmosphere.

CFCs cause a considerable amount of breakdown in the ozone layer reacting with the ozone molecule. Since the late 1970s, ozone depletion has been a major environmental concern. The Industrial Revolution released a lot of pollutants, but ozone depletion has been mostly caused by manufactured chemicals, especially halocarbons, since the mid-20th century.

The gradual decrease in ozone concentration has been largely caused by human-made emissions of ozone-depleting substances (ODS). Chlorofluorocarbons (CFCs), halocarbons, solvents, propellants, and refrigerants are some of them. Some ozone-depleting substances come from natural sources, but the dramatic rise in chlorine and bromine levels from industrial compounds has drastically accelerated ozone depletion.

What Are the Main Ozone Depleting Substances (ODS)?

Ozone layer depletion is caused by CFCs, HCFCs, Halogens, Carbon Tetrachloride, and Methyl Chloroform. All these depleting substances are explained below:

CFCs

CFCs stand for Chlorofluorocarbons. It is mainly used in cooling appliances such as refrigerators, and air conditioners. Also used in dry cleaning agents, industrial solvents, hospital sterilizers, and foaming products like mattresses, cushions, etc.

Five types of CFCs in the atmosphere increased from 2010 to 2020, reaching record levels in 2020 despite being banned under the Montreal Protocol. This rise is alarming since CFCs were supposed to be phased out by 2010.

HCFCs

It stands for Hydrochlorofluorocarbons. HCFCs also get their way into the atmosphere through various human activities like vehicles and many other industrial emissions. They’re common in refrigeration, air conditioning, and foam blowing. As hydrogen atoms are present in HCFCs, they decompose before they reach the stratosphere, which makes them behave differently from CFCs. They still harm Earth’s atmosphere.

HCFCs destroy 98% less ozone than CFCs, but they’re still greenhouse gases and cause global warming. HCFCs are less potent than CFCs, but still significantly more potent than CO2.

Halons

Halons are used in specific fire extinguishers and also affect the ozone molecules present in the atmosphere. Fire suppression uses halons, which contain bromine, which are powerful ozone-depleting chemicals. They are controlled under the Montreal Protocol.

Carbon Tetrachloride

Carbon tetrachloride (CTC) is also used in some specific extinguishers and solvents. It is also written as CCl4. The EPA proposed new regulations for CTC in July 2023 to protect workers and communities. CTC is used as a solvent in commercial settings and to make other chemicals. These new rules aim to limit its use, reducing exposure risks and improving workplace safety. According to the EPA, CTC poses an unreasonable risk to health, including liver toxicity and cancer from chronic inhalation and dermal exposure, particularly to workers.

Methyl Chloroform

Methyl chloroform is widely used in different industries such as vapor degreasing, adhesives & some aerosols, cold cleaning, chemical processing, etc. In 1987, the Montreal Protocol banned methyl chloroform as an industrial solvent because of its ozone-depleting properties. Global emissions decreased a lot in the 1990s, but recent measurements indicate they’ve been higher than expected in Europe. The global tropospheric hydroxyl radical (OH) concentrations are affected by these ongoing emissions.

What Causes Ozone Depletion?

Below are the major causes of the ozone layer depletion and how they affect the environment:

Human-Made Causes of Ozone Layer Depletion

Human-made causes include the emission of CFCs, HCFCs, Halons, Chlorine Monoxide (ClO) reactions, additional chemicals, and rocket launches. These are described below:

Chlorofluorocarbons (CFCs) Emissions

The triatomic form of oxygen found in Earth’s atmosphere is termed O3 i.e., ozone. CFCs are one of the major causes of ozone layer depletion.

The primary reasons that provoke ozone depletion include lower temperatures and higher concentrations of chlorine & bromine in the upper layer of the stratosphere.

The traditional sources of CFC emissions are soaps, insulating foams, solvents, spray aerosols, takeaway containers, cooling equipment like refrigerators & ACs, etc. All these used chlorofluorocarbons. Since CFC-containing products were widely used in the past, significant amounts of these compounds have been accumulated in the atmosphere.

When the CFCs enter the stratosphere layer, they start affecting the ozone layer. The CFC molecules start breaking into chlorine atoms through ultraviolet radiation. When these chlorine atoms react with an ozone molecule, it affects the entire chemical cycle of the ozone layer. As a result, it causes a hole in the ozone layer.

Researchers were surprised to see recent increases in some CFCs even though overall CFC emissions have declined since the 1980s (5% of their highest levels). This is important to know because the ozone hole over Antarctica is still expected to heal by around 2060, even with these increases in CFCs.

Emission of Hydrochlorofluorocarbons (HCFCs)

CFCs are the primary cause of the hole in the ozone layer, while HCFCs are the secondary cause.

HCFCs and other ozone-depleting substances (ODS) are quite common to be emitted through various human activities. These activities include the use of vehicles, emissions from industries and factories, and the use of refrigerants and aerosols containing ozone-depleting substances.

These ODS are comparatively stable in the lower layers of Earth’s atmosphere. On the other hand, when it reaches the stratosphere layer of Earth’s atmosphere, it gets exposed to UV radiation, where it breaks down and releases chlorine atoms.

The US EPA made big changes to reduce the use of hydrofluorocarbons (HFCs). These were used instead of CFCs and HCFCs. The new rule limits HFCs in products because they warm the planet a lot. This follows the American Innovation and Manufacturing Act of 2020. The goal is to cut down HFC use greatly by the years 2024 (40%) and 2036 (85%). There’s also a plan to better handle and reuse existing HFCs, which are strong greenhouse gases.

Ozone Depletion via Chlorine Monoxide (ClO) Reaction

When free chlorine atoms (present in the atmosphere) react with O3 (ozone), they form ClO (chlorine monoxide) and an oxygen molecule. This chlorine monoxide then reacts with an ozone molecule to form a chlorine atom and two oxygen molecules. Again, this chlorine atom forms chlorine monoxide by reacting with the ozone molecule. This ongoing cycle of reactions contributes immensely to the depletion of the ozone layer in the Earth’s stratosphere.

Emission of Halons

Halons, similar to chlorofluorocarbons (CFCs), are also responsible for depleting the ozone layer. These compounds are often used in fire extinguishers and fire suppression systems, as they contain bromine and chlorine, which interrupt combustion. But they have a big impact on the environment.

As halons travel through the atmosphere, they eventually reach the stratosphere, where the ozone layer is situated. These halon molecules are broken down by intense ultraviolet (UV) radiation, releasing bromine and chlorine atoms.

As bromine and chlorine react with ozone (O3), they break down the ozone molecules into oxygen (O2), which depletes the protective layer of ozone. Because of this depletion, more harmful UV radiation gets to the Earth’s surface.

Additional Chemicals Contributing to Ozone Depletion

Apart from CFCs, HCFCs, and other ODS, many other chemicals influence ozone depletion. Some of these include chlorine compounds (Clx), nitrogen oxides (NOy), and others. Volatile Organic Compounds (VOCs) are also relevant in the environmental context.

These chemicals belong to different categories. Many of these chemicals are chlorine and nitrogen-based compounds, each affecting the ozone layer differently.

These chemicals also affect the ozone layer when react with ozone atoms near the stratosphere layer of Earth’s atmosphere.

Rocket Launches

Rocket launches also contribute to ozone depletion, mainly due to emissions released into the stratosphere. Their launches have a noticeable impact on the ozone layer, but it’s considered less significant than the historical effects of CFCs and HCFCs. According to some studies, rocket launches could have an even greater impact on the ozone layer in the future, but the extent of this impact is still being studied.

All of the above were human-made causes of ozone layer depletion. Below are some natural causes:

Natural Causes of Ozone Layer Depletion

The natural causes mainly include volcanic eruptions, natural atmospheric chemistry, sunspots, and solar activity. These are discussed below:

Volcanic Eruptions

When volcanoes erupt, they emit gases and particles into the atmosphere. At high altitudes, sulfur dioxide (SO2) converts into sulfuric acid aerosols. Aerosols provide surfaces for chemical reactions that can deplete ozone. Chlorine and bromine, which are naturally present in the stratosphere, are involved in these reactions.

A prominent example was Mount Pinatubo eruption in 1991. There was a temporary but major depletion of ozone. However, such large volcanic eruptions are rare.

As of 2023, scientists are monitoring volcanic activities and their potential impacts on the ozone layer. Volcanic eruptions don’t have the same impact on ozone depletion as human-made CFCs.

Natural Atmospheric Chemistry

There’s a natural cycle that forms and breaks down the ozone layer. When oxygen molecules (O2) interact with UV light, ozone (O3) is created, and it’s broken down naturally.

As water vapor and methane naturally form in the atmosphere, they can create hydrogen oxides and nitrogen oxides, which contribute to ozone depletion. Researchers are still studying these natural chemical processes, especially how they mix with changes humans make in the air.

Sunspots and Solar Activity

Sunspots are dark areas of the sun. They are cooler than other parts. They show more solar activity like solar flares and big solar energy bursts. This activity sends more UV and X-ray rays to our upper atmosphere and affects the ozone layer. How this activity changes the ozone is not simple. Increased UV radiation can both generate and break down ozone molecules.

Data from NASA’s Solar Dynamics Observatory continues to provide insights into solar activity in 2023. While solar activity does affect the ozone layer, it has a more cyclical effect because of the 11-year solar cycle. During this solar cycle, the Sun’s activity changes. It takes 11 years for the Sun to go from very active to less active, and then back to very active.

While natural factors do impact the ozone layer, historically human-made chemicals have done the most damage, especially CFCs.

Interconnection Between Global Warming and Ozone Layer Depletion

Global warming is one of the big environmental issues at present. It is affecting the environment in different ways, starting from climate change, and extreme weather events, disturbing the ecosystem and biodiversity of the planet. Its indirect effects may also interact with factors influencing the ozone layer.

Various atmospheric processes are affected by greenhouse gases, which cause the troposphere (atmospheric layer below the stratosphere) to absorb more heat.

The ozone layer, where the stratosphere is located, has different thermal dynamics than the troposphere, with different factors affecting it.

The main cause of ozone depletion is chemical reactions involving substances that deplete the ozone layer. A lot of factors influence its recovery, including sunlight and atmospheric chemistry.

While global warming and ozone depletion are driven by different processes and chemicals, they are interconnected in complex ways. Global warming is caused by greenhouse gases, which can cause cooling in the stratosphere, which affects the chemistry of the ozone layer. For example, changing climate can change wind patterns and temperatures, impacting ozone distribution.

Some ozone-depleting substances are potent greenhouse gases, so reducing them helps mitigate global warming. Furthermore, ozone depletion can cause indirect effects on climate systems from increased ultraviolet radiation. It’s true that global warming and ozone depletion cause and affect the Earth’s atmosphere in different ways, their interaction within the atmosphere results in complex and interconnected effects.

Conclusion

Ozone layer depletion is one of the big crises for humankind. Ozone depletion results in increasing ultraviolet radiation hitting the Earth’s surface. Increasing UV exposure can cause skin cancer, cataracts, and other health problems in humans, as well as negative effects on wildlife, marine creatures, and plants. International agreements, especially the Montreal Protocol, are trying to phase out ozone-depleting substances.

Hence, we should spread awareness among all our peer groups about the causes of ozone layer depletion (both human and natural ones). We also need to be aware of the harmful effects of ozone depletion and how we can handle this vital environmental issue.

We should try to handle ozone layer depletion at an individual level. Try to minimize the use of products, appliances, equipment, etc. that emit ODS (ozone-depleting substances). Our continuous attempt will work to make this planet a sustainable place to live for each organism peacefully.