subtopic 6.4: Stratospheric Ozone
image from http://en.wikipedia.org/wiki/Ozone_layer
The ozone layer is the part of the Earth's atmosphere which contains relatively high concentrations of ozone (O3). "Relatively high" means a few parts per million - much higher than the concentrations in the lower atmosphere but still small compared to the main components of the atmosphere. Although the concentration of ozone in the ozone layer is very small, it is vitally important to life because it absorbs biologically harmful ultraviolet (UV) radiation from the Sun. The "thickness" of the ozone layer - that is, the total amount of ozone in a column overhead - varies by a large factor worldwide, being in general smaller near the equator and larger as one moves towards the poles. It also varies with season, being in general thicker during the spring and thinner during the autumn.
In this unit unit we will look at how human activities have resulted in the depletion of the ozone layer and the roles of government and non-government agencies in controlling the restricting ozone depleting substances.
This unit is a minimum of SL 2 hours.
In this unit unit we will look at how human activities have resulted in the depletion of the ozone layer and the roles of government and non-government agencies in controlling the restricting ozone depleting substances.
This unit is a minimum of SL 2 hours.
Guiding questions:
- How does the ozone layer maintain equilibrium?
- How does human activity change this equilibrium?
Understanding
solar radiation
6.4.1 The Sun emits electromagnetic radiation in a range of wavelengths, from low frequency radio waves to high frequency gamma radiation.
- Explain how different categories of UV radiation (UVA, UVB, UVC) vary in their effects on living organisms.
The Sun emits energy in the form of electromagnetic radiation, which spans a broad spectrum of wavelengths. This spectrum includes, from longest to shortest wavelength: radio waves, microwaves, infrared (heat), visible light, ultraviolet (UV) light, X-rays, and gamma rays. The visible light portion of the spectrum is essential for human vision, allowing us to perceive colors from red (longer wavelengths) to violet (shorter wavelengths). In addition, visible light is crucial for photosynthesis in plants, which primarily use blue and red light to convert light energy into chemical energy, fueling ecosystems on Earth.
https://www.cdc.gov/radiation-health/about/electromagnetic-spectrum.html
6.4.2 Shorter wavelengths of radiation (namely, UV radiation) have higher frequencies and, therefore, more energy, so pose an increased danger to life.
- Outline how in the absence of pollution, stratospheric ozone provides an example of a dynamic equilibrium.
- Explain why seasonal changes occur in stratospheric ozone over the Polar Regions
Ozone plays a key role in the temperature structure of the Earth's atmosphere. Without the filtering action of the ozone layer, more of the Sun's UV-B radiation would penetrate the atmosphere and would reach the Earth's surface. Ultraviolet radiation is absorbed during the formation and destruction of ozone from oxygen. You do not need to memorise chemical equations is not required.
The Sun also emits ultraviolet (UV) radiation, which is divided into three categories based on wavelength:
- UVA (320–400 nm): The least harmful form of UV radiation, UVA makes up approximately 95% of the UV radiation reaching Earth’s surface. It can penetrate deep into the skin and contribute to premature aging and DNA damage, but it is not absorbed by ozone.
- UVB (280–320 nm): UVB is partially absorbed by the ozone layer, with about 5% reaching Earth’s surface. It is more harmful than UVA and can cause sunburn, skin cancer, and damage to the eyes and immune system.
- UVC (100–280 nm): The most dangerous type of UV radiation, UVC is almost completely absorbed by the ozone layer and oxygen in the atmosphere. Fortunately, very little of it reaches the Earth's surface.
STRATOSPHERIC OZONE
6.4.3 Stratospheric ozone absorbs UV radiation from the Sun, reducing the amount that reaches the Earth’s surface and, therefore, protecting living organisms from its harmful effects.
- Explain how stratospheric ozone protects living organisms from UV radiation.
image from www.chemhume.co.uk
The stratospheric ozone layer plays a critical role in absorbing ultraviolet (UV) radiation from the Sun, reducing the amount that reaches the Earth's surface and protecting living organisms from its harmful effects. UV radiation is high-energy radiation, particularly at shorter wavelengths (UVB and UVC). These shorter wavelengths have enough energy to damage biological molecules, such as DNA, leading to mutations, cancers, and other detrimental effects in living organisms.
Ozone (O₃) absorbs the majority of UVB and UVC radiation.
While UVC radiation (100–280 nm) is almost completely absorbed by ozone and oxygen in the stratosphere, UVB (280–320 nm) is only partially absorbed, with a small fraction reaching the Earth's surface. This absorption is essential for protecting ecosystems, as excessive UVB radiation can damage the cells of plants and animals. UVA radiation (320–400 nm), which is not absorbed by ozone, penetrates the atmosphere and can also cause skin aging and DNA damage, though it is less harmful than UVB and UVC.
The ozone layer acts as a protective barrier by absorbing high-energy UV radiation and preventing it from directly impacting living organisms. Without this protection, Earth would be exposed to significantly higher levels of UV radiation, resulting in severe environmental and health consequences, including increased rates of skin cancer, eye damage, and disruptions to ecosystems.
While UVC radiation (100–280 nm) is almost completely absorbed by ozone and oxygen in the stratosphere, UVB (280–320 nm) is only partially absorbed, with a small fraction reaching the Earth's surface. This absorption is essential for protecting ecosystems, as excessive UVB radiation can damage the cells of plants and animals. UVA radiation (320–400 nm), which is not absorbed by ozone, penetrates the atmosphere and can also cause skin aging and DNA damage, though it is less harmful than UVB and UVC.
The ozone layer acts as a protective barrier by absorbing high-energy UV radiation and preventing it from directly impacting living organisms. Without this protection, Earth would be exposed to significantly higher levels of UV radiation, resulting in severe environmental and health consequences, including increased rates of skin cancer, eye damage, and disruptions to ecosystems.
Activity: Use UV-sensitive beads to investigate the impact of UV exposure under different conditions. They can simulate the effects of the ozone layer using filters and compare the color change in the beads under direct sunlight and through different barriers (e.g., sunscreen or fabric)
6.4.4 UV radiation reduces photosynthesis in phytoplankton and damages DNA by causing mutations and cancer. In humans, it causes sunburn, premature ageing of the skin and cataracts.
- Explain the effects of increased UVB radiation on human health, focusing on skin cancer, eye damage, and immune system suppression
- Discuss the impacts of ozone depletion on marine ecosystems
Human Health Impacts:
Increased exposure to UVB radiation poses significant risks to human health. Some of the most serious consequences include:
Increased exposure to UVB radiation poses significant risks to human health. Some of the most serious consequences include:
- Skin Cancer: UVB radiation is a major cause of skin cancer, including both non-melanoma and melanoma forms. Prolonged and unprotected exposure to UVB increases the likelihood of DNA damage, leading to mutations that can result in the uncontrolled cell growth associated with cancer. Melanoma is particularly dangerous because it spreads more rapidly than other skin cancers.
- Cataracts and Eye Damage: UVB radiation can also cause cataracts, a clouding of the lens in the eye that can lead to blindness. Increased UV exposure accelerates the formation of cataracts, especially in populations with limited access to protective eyewear.
- Immune System Suppression: UV radiation has been shown to suppress the immune system, making individuals more susceptible to infections and reducing the body’s ability to fight off diseases. This is particularly concerning in regions with already high UV exposure and where medical resources may be limited.
https://www.sciencedirect.com/science/article/pii/S0160412024001211
Impacts on Aquatic Ecosystems:
Aquatic ecosystems, particularly those in the upper layers of oceans and lakes, are sensitive to increased UVB radiation. Phytoplankton, which forms the base of the marine food web, is highly vulnerable to UVB damage. This can disrupt entire marine ecosystems:
Impacts on Terrestrial Ecosystems:
UVB radiation also affects terrestrial ecosystems, particularly plant life. Increased UV exposure can alter plant growth patterns, nutrient cycling, and species composition:
Human Livelihoods and Socio-Economic Impacts:
The environmental changes caused by ozone depletion can have broader socio-economic impacts:
Aquatic ecosystems, particularly those in the upper layers of oceans and lakes, are sensitive to increased UVB radiation. Phytoplankton, which forms the base of the marine food web, is highly vulnerable to UVB damage. This can disrupt entire marine ecosystems:
- Phytoplankton Reduction: UVB radiation inhibits the photosynthesis process in phytoplankton, reducing their productivity. This has cascading effects throughout the food chain, as phytoplankton are a primary food source for many marine organisms, including zooplankton, fish, and marine mammals. A decline in phytoplankton populations can lead to reduced fish stocks and altered biodiversity.
- Coral Reef Damage: Coral reefs, already vulnerable to climate change and ocean acidification, are also affected by increased UVB radiation. Excessive UV exposure can damage the symbiotic algae (zooxanthellae) living in corals, leading to bleaching events where corals lose their color and are unable to sustain themselves. Coral bleaching disrupts reef ecosystems, which support diverse marine life.
Impacts on Terrestrial Ecosystems:
UVB radiation also affects terrestrial ecosystems, particularly plant life. Increased UV exposure can alter plant growth patterns, nutrient cycling, and species composition:
- Reduced Plant Productivity: Many plant species are sensitive to UVB radiation, which can damage plant tissues and reduce their ability to photosynthesize efficiently. This affects crop yields and food security, particularly in regions already facing agricultural challenges.
- Changes in Species Composition: As some plants are more resistant to UVB than others, increased UV exposure may shift the balance of ecosystems, allowing UV-resistant species to dominate. This can reduce biodiversity and disrupt existing ecosystems by altering predator-prey relationships and competitive dynamics.
Human Livelihoods and Socio-Economic Impacts:
The environmental changes caused by ozone depletion can have broader socio-economic impacts:
- Agriculture: Reduced plant productivity affects food security, especially in agricultural regions dependent on crops that are sensitive to UV radiation. This can lead to economic losses for farmers and increases in food prices.
- Fisheries: Declines in fish populations due to disruptions in the marine food web can threaten commercial fisheries, affecting the livelihoods of communities dependent on fishing.
- Tourism: Increased UV radiation can also impact tourism, particularly in regions reliant on outdoor activities. Concerns over health risks such as skin cancer may deter tourists from visiting high UV exposure areas, such as beaches or coral reefs affected by bleaching.
Beneficial Effects of UV Radiation
While UV radiation has several harmful effects, it also plays a beneficial role in human health. UVB radiation stimulates the production of vitamin D in the skin, which is essential for maintaining healthy bones and supporting the immune system. Additionally, small doses of UV radiation can be used in sterilization processes, as it effectively kills bacteria and viruses. UV light is also used in phototherapy to treat certain skin conditions like psoriasis and eczema, demonstrating its therapeutic applications when applied in controlled environments.
While UV radiation has several harmful effects, it also plays a beneficial role in human health. UVB radiation stimulates the production of vitamin D in the skin, which is essential for maintaining healthy bones and supporting the immune system. Additionally, small doses of UV radiation can be used in sterilization processes, as it effectively kills bacteria and viruses. UV light is also used in phototherapy to treat certain skin conditions like psoriasis and eczema, demonstrating its therapeutic applications when applied in controlled environments.
Human activities have introduced ozone-depleting substances (ODSs) into the atmosphere, particularly chlorofluorocarbons (CFCs) and halons. These substances are stable in the lower atmosphere but are broken down by UV radiation in the stratosphere, releasing chlorine and bromine atoms. These halogens catalyze the breakdown of ozone molecules, disrupting the natural balance of ozone formation and destruction. One chlorine atom can destroy thousands of ozone molecules before being deactivated.
Application of Skills:
Consider data related to the impacts of UV radiation
Consider data related to the impacts of UV radiation
6.4.5 The relative concentration of ozone molecules has stayed constant over long periods of time due to a steady state of equilibrium between the concurrent processes of ozone formation and destruction.
- Explain how the dynamic equilibrium of the ozone layer is maintained
The ozone layer is maintained through a dynamic equilibrium, where ozone (O₃) molecules are constantly formed and destroyed. Ozone is created when UV-C radiation splits oxygen molecules (O₂), forming oxygen atoms (O), which then combine with O₂ to produce ozone (O₃). This ozone absorbs UV radiation (mainly UVB and UVC) and breaks back down into oxygen molecules and atoms, maintaining a balance.
Stratospheric ozone is formed naturally by chemical reactions involving solar ultraviolet radiation (sunlight) and oxygen molecules, which make up 21% of the atmosphere.
- solar ultraviolet radiation breaks apart one oxygen molecule (O2) to produce two oxygen atoms (2 O)
- each of these highly reactive atoms combines with an oxygen molecule to produce an ozone molecule (O3).
- these reactions occur continually whenever solar ultraviolet radiation is present in the stratosphere. As a result, the largest ozone production occurs in the tropical stratosphere
OZONE DEPLETION
6.4.6 Ozone-depleting substances (ODSs) destroy ozone molecules, augmenting the natural ozone breakdown process
- Explain how ODSs, such as CFCs, lead to the destruction of ozone in the stratosphere
- Evaluate the role of human activities in contributing to ozone depletion through the use of ODSs
When rates of ozone formation and depletion are unequal, the equilibrium will tip to increase in formation or destruction. Human activities have introduced ozone-depleting substances (ODSs) into the atmosphere, particularly chlorofluorocarbons (CFCs) and halons. These substances are stable in the lower atmosphere but are broken down by UV radiation in the stratosphere, releasing chlorine and bromine atoms. These halogens catalyze the breakdown of ozone molecules, disrupting the natural balance of ozone formation and destruction. One chlorine atom can destroy thousands of ozone molecules before being deactivated.
NOTE: Ozone depletion is not a cause of global warming.
NOTE: Ozone depletion is not a cause of global warming.
Halogenated organic gases are very stable under normal conditions but can liberate halogen atoms when exposed to ultraviolet radiation in the stratosphere. These atoms react with monatomic oxygen and slow the rate of ozone
re‑formation. Pollutants enhance the destruction of ozone, thereby disturbing the equilibrium of the ozone production system
Ozone-depleting substances (ODS)
re‑formation. Pollutants enhance the destruction of ozone, thereby disturbing the equilibrium of the ozone production system
Ozone-depleting substances (ODS)
- Chlorofluorocarbons (CFCs or freons) - propellants in spray cans, foam, refrigerants
- Hydrochlorofluorocarbons (HCFCs) - replacements for CFCs
- Halon - fire extinguishers
- Methyl bromide - pesticides
- Nitrogen oxides - bacterial breakdown of nitrites and nitrates in the soil, supersonic aircraft
- Carbon tetrachloride - cleaning substance
How ozone is depleted by CFC’s:
- UV radiation breaks off a chlorine atom from a CFC molecule.
- The chlorine atom attacks an ozone molecule (O3), breaking it apart and destroying the ozone.
- The result is an ordinary oxygen molecule (O2) and a chlorine monoxide molecule (ClO).
- The chlorine monoxide molecule (ClO) is attacked by a free oxygen atom releasing the chlorine atom and forming an ordinary oxygen molecule (O2).
from http://www.ucar.edu/learn/1_6_1.htm
image from www.esrl.noaa.gov
NOTE: The chemical equations relating to the formation and destruction of ozone are required for SL
impacts of ozone depletion
6.4.7 Ozone depletion allows increasing amounts of UVB radiation to reach the Earth’s surface, which impacts ecosystems and human health.
- Describe how polar stratospheric clouds contribute to the formation of ozone holes over the poles
- Discuss why ozone depletion is more severe over Antarctica compared to the Arctic
Ozone depletion in polar regions, particularly over Antarctica, is most severe during the spring, when the "ozone hole" reaches its peak. This seasonal depletion is caused by a combination of unique chemical and atmospheric conditions found in the polar stratosphere. The main factors contributing to this phenomenon are extreme cold temperatures, the formation of polar stratospheric clouds (PSCs), and the presence of ozone-depleting substances (ODSs) in the atmosphere
Key Processes in Polar Ozone Depletion:
- During the polar winter, temperatures in the stratosphere drop below -78°C, allowing PSCs to form. These clouds consist of tiny ice crystals and nitric acid. PSCs provide surfaces for chemical reactions that convert inactive chlorine and bromine compounds (produced by ODSs like CFCs) into their reactive forms, such as chlorine monoxide (ClO) and bromine monoxide (BrO).
- When sunlight returns to the polar regions in the spring, UV radiation triggers chemical reactions involving these reactive chlorine and bromine species. These reactions rapidly break down ozone (O₃) molecules into oxygen (O₂), depleting the ozone layer.
- The ozone hole is most prominent during the Antarctic spring (September to November). During this period, the combination of sunlight, reactive chlorine and bromine, and PSC surfaces leads to rapid ozone depletion. The depletion is more pronounced in Antarctica than in the Arctic because the Antarctic vortex—a circular wind pattern—isolates the air above the continent, allowing PSCs to persist for longer periods.
https://theconversation.com/antarctic-ozone-recovery-will-be-a-long-and-bumpy-road-22429
The total amount of ozone that constitutes the atmosphere is measured in Dobson Units (DU), which is a value determine by measuring the concentration of ozone molecules in a column of air that extends from the Earth’s surface to the top of the atmosphere. Areas with values less than 220 Dobson Units are considered to have experienced severe ozone destruction. The image below presents a color-coded scale for Dobson Units that shows the 220-unit cut-off below which the concentration of ozone is recognized as being low enough that it poses a danger to human health. Please note which colors represent high ozone concentrations and which colors represent low ozone concentrations.
https://www.esa.int/Enabling_Support/Preparing_for_the_Future/Space_for_Earth/Antarctic/Satellite_observations_monitor_ozone_hole
Volcanic Aerosols:
Volcanic eruptions can enhance ozone depletion by injecting sulfur compounds into the stratosphere, where they contribute to the formation of additional surfaces for chemical reactions on PSCs. This further accelerates the breakdown of ozone molecules.
Volcanic eruptions can enhance ozone depletion by injecting sulfur compounds into the stratosphere, where they contribute to the formation of additional surfaces for chemical reactions on PSCs. This further accelerates the breakdown of ozone molecules.
6.4.7 Ozone depletion allows increasing amounts of UVB radiation to reach the Earth’s surface, which impacts ecosystems and human health.
- Explain how ozone depletion leads to increased UVB radiation reaching Earth’s surface
- Discuss why ozone depletion is more severe at the poles during spring
Ozone depletion refers to the thinning of the ozone layer, which allows greater amounts of ultraviolet B (UVB) radiation to reach the Earth’s surface. Stratospheric ozone, which absorbs much of the harmful UVB radiation from the Sun, has been significantly depleted due to the release of ozone-depleting substances (ODSs), such as chlorofluorocarbons (CFCs). This depletion has affected the entire globe, not just specific regions, but is particularly severe at the poles.
Ozone depletion is most visible in the form of ozone "holes" that appear each spring over the polar regions, especially Antarctica. These seasonal ozone holes are caused by a combination of chemical and atmospheric factors, including the presence of ODSs and specific weather patterns that are unique to polar regions.
Ozone depletion is most visible in the form of ozone "holes" that appear each spring over the polar regions, especially Antarctica. These seasonal ozone holes are caused by a combination of chemical and atmospheric factors, including the presence of ODSs and specific weather patterns that are unique to polar regions.
Global and Polar Ozone Depletion:
- Global Impact: Ozone depletion is not limited to the polar regions; it has affected the stratosphere over the entire planet. As the ozone layer thins, more UVB radiation passes through the atmosphere, increasing the risk of harm to ecosystems and human health globally.
- Polar Ozone Holes: At the poles, particularly over Antarctica, ozone depletion is more pronounced due to the formation of ozone holes. These holes appear during the spring (September-November in the Southern Hemisphere) as a result of seasonal weather patterns, such as the Antarctic vortex. This circular wind pattern traps cold air and allows polar stratospheric clouds (PSCs) to form. PSCs provide surfaces for chemical reactions that convert ODSs into reactive chlorine and bromine compounds, which then catalytically destroy ozone molecules when sunlight returns in the spring.
Finn Bjørklid, Norwegian Institute for Air Research (NILU).
Ozone Depletion and Polar Weather Patterns:
The polar regions experience particularly severe ozone depletion due to the unique weather patterns that occur during their winter. The Antarctic vortex traps cold air, leading to the formation of PSCs. These clouds provide surfaces for the reactions that convert inactive forms of chlorine and bromine into highly reactive species. When sunlight returns in the spring, these reactive compounds catalyze the rapid destruction of ozone, forming the ozone hole. Although the Arctic experiences similar conditions, the ozone depletion is usually less severe due to milder weather patterns.
The polar regions experience particularly severe ozone depletion due to the unique weather patterns that occur during their winter. The Antarctic vortex traps cold air, leading to the formation of PSCs. These clouds provide surfaces for the reactions that convert inactive forms of chlorine and bromine into highly reactive species. When sunlight returns in the spring, these reactive compounds catalyze the rapid destruction of ozone, forming the ozone hole. Although the Arctic experiences similar conditions, the ozone depletion is usually less severe due to milder weather patterns.
MITIGATION STRATEGIES
6.4.8 The Montreal Protocol is an international treaty that regulates the production, trade and use of chlorofluorocarbons (CFCs) and other ODSs. It is regarded as the most successful example yet of international cooperation in management and intervention to resolve a significant environmental issue.
- Evaluate the success of the Montreal Protocol in reducing ozone depletion
- Discuss how international cooperation through the Montreal Protocol has helped mitigate ozone depletion
Strategies for Reducing Ozone Depletion
Pollution management may be achieved by reducing the manufacture and release of ozone-depleting substances. Methods for this reduction include:
- recycling refrigerants
- developing alternatives to gas-blown plastics, halogenated pesticides, propellants and aerosols
- developing non-propellant alternatives.
The Montreal Protocol
The Montreal Protocol on Substances that Deplete the Ozone Layer is an international treaty, adopted in 1987, that regulates the production, trade, and use of ozone-depleting substances (ODSs), particularly chlorofluorocarbons (CFCs). It is widely regarded as one of the most successful examples of international environmental cooperation, having led to significant reductions in the emissions of ODSs, and as a result, the ozone layer is gradually recovering.
The success of the Montreal Protocol is attributed to several key factors:
The success of the Montreal Protocol is attributed to several key factors:
- Global Participation: The treaty has been ratified by almost every country in the world, making it the first universally ratified treaty in United Nations history. This global participation was critical because ODSs, once released into the atmosphere, disperse globally and affect the ozone layer regardless of where they are emitted.
- Legally Binding: The protocol includes legally binding agreements that require countries to phase out the production and use of ODSs. It also established compliance mechanisms, making it difficult for nations to ignore their commitments.
- Flexibility and Adaptation: The Montreal Protocol has been amended several times to adjust to new scientific knowledge and to phase out additional harmful chemicals. The Kigali Amendment (2016), for instance, introduced measures to phase out hydrofluorocarbons (HFCs), which do not deplete the ozone layer but are potent greenhouse gases.
- Financial and Technical Assistance: Developed countries under the protocol have provided financial and technical assistance to developing nations to help them transition away from ODSs. This support has been essential in ensuring global compliance and the success of the treaty.
- Scientific Consensus: The protocol was based on a solid foundation of scientific research that demonstrated the harmful effects of ODSs on the ozone layer. The clear link between ODS emissions and ozone depletion helped garner global support and urgency for action.
UNEP (United Nations Environment Programme), forges international agreements, studies the effectiveness of these agreements, and the difficulties implementing and enforcing them.
- The Montreal Protocol (1987), which is an international agreement on reduction of emission of ozone-depleting substances.
- The signatories agreed to freeze production of many CFCs and halons and strongly reduce consumption and production of these substances by 2000.
- People from many different backgrounds have come together from across the world including scientists, industrialists, researchers, policy and law makers, to work together on a common cause.
- Most countries followed the rules but China and India continued to produce and use huge amounts of CFCs.
- But they have since both agreed to phase out the use of CFCs.
- Therefore, the Montreal Protocol is often used as an exemplar of successful international cooperation
Model of Cooperation
The Montreal Protocol has largely been a success
- The success of the protocol shows that science-based policy and international cooperation can address global issues effectively.
- An example of the precautionary principle
- Designed in such a way countries could phase out ODSs at different times depending on their economic status
- An example of collaboration between experts in different fields coming together to solve a problem
- First protocol with regulations that were carefully monitored
6.4.9 Actions taken in response to the Montreal Protocol have prevented the planetary boundary for stratospheric ozone depletion being crossed.
- Explain how the Montreal Protocol has prevented the crossing of the planetary boundary for ozone depletion
- Analyze the trend in ozone hole size over time and evaluate what it indicates about the success of the Montreal Protocol.
The planetary boundary for stratospheric ozone depletion represents a threshold where the ozone layer becomes too thin to protect Earth from harmful ultraviolet B (UVB) radiation. If crossed, this could result in severe damage to human health and ecosystems. However, thanks to the actions taken under the Montreal Protocol, this boundary has not been crossed.
The Montreal Protocol, adopted in 1987, successfully regulated the production and use of ozone-depleting substances (ODSs), such as chlorofluorocarbons (CFCs). These efforts led to a significant reduction in global ODS emissions, allowing the ozone layer to slowly recover.
Evidence from Ozone Hole Data:
The ozone hole over Antarctica, which peaked in the late 1990s, has shown signs of stabilization and recovery since the early 2000s. For instance:
By preventing further depletion, the Montreal Protocol has successfully kept the planetary boundary for ozone depletion from being crossed, demonstrating how effective international cooperation can address global environmental issues
The Montreal Protocol, adopted in 1987, successfully regulated the production and use of ozone-depleting substances (ODSs), such as chlorofluorocarbons (CFCs). These efforts led to a significant reduction in global ODS emissions, allowing the ozone layer to slowly recover.
Evidence from Ozone Hole Data:
The ozone hole over Antarctica, which peaked in the late 1990s, has shown signs of stabilization and recovery since the early 2000s. For instance:
- 1990s: The ozone hole reached a maximum size of nearly 30 million square kilometers in 2000.
- 2000s-Present: Since the Montreal Protocol, the size of the ozone hole has fluctuated but has been steadily decreasing. Current trends suggest the ozone layer could return to pre-1980 levels by mid-century.
By preventing further depletion, the Montreal Protocol has successfully kept the planetary boundary for ozone depletion from being crossed, demonstrating how effective international cooperation can address global environmental issues
https://isetnepal.org.np/the-ozone-layer-is-healing-new-study-finds/
UNEP has had a key role in providing information, and creating and evaluating international agreements, for the protection of stratospheric ozone.
United Nations Environment Programme (UNEP) in forging international agreements
United Nations Environment Programme (UNEP) in forging international agreements
- ITIHC (International Trade in Harmful Chemicals)
- air pollution
- contamination of international waterways
- provide information to countries and public on disadvantages of pollution
- brought together 24 countries in 1987 to sign the initial Montreal Protocol on Substances that Deplete the Ozone Layer
hl only
6.4.10 ODSs release halogens, such as chlorine and fluorine, into the stratosphere, which break down ozone.
- Explain how CFCs contribute to the destruction of ozone in the stratosphere
- Compare the roles of chlorine and fluorine in catalyzing the breakdown of ozone
Ozone-depleting substances (ODSs), like chlorofluorocarbons (CFCs) and halons, are stable in the lower atmosphere but break down under ultraviolet (UV) radiation when they reach the stratosphere. This process releases highly reactive halogen atoms, such as chlorine (Cl) and fluorine (F), which are responsible for ozone depletion.
Chlorine’s Role in Ozone Destruction:
When CFCs are exposed to UV radiation, they break apart, releasing chlorine atoms:
Chlorine’s Role in Ozone Destruction:
When CFCs are exposed to UV radiation, they break apart, releasing chlorine atoms:
http://icestories.exploratorium.edu/dispatches/the-ozone-holeits-still-there/index.html
These chlorine atoms catalyze the destruction of ozone (O₃) by breaking it down into oxygen (O₂), and the chlorine atom is regenerated, allowing it to continue destroying ozone in a cycle:
A single chlorine atom can destroy thousands of ozone molecules, leading to significant ozone depletion over time.
Fluorine and Other Halogens:
Though chlorine plays the primary role in ozone depletion, fluorine and bromine from halons also contribute. Bromine, in particular, is highly efficient at destroying ozone and is even more damaging than chlorine.
Impact on the Ozone Layer:
This ongoing breakdown of ozone leads to the thinning of the ozone layer, especially over the polar regions. As a result, increased amounts of ultraviolet B (UVB) radiation reach the Earth's surface, causing harmful effects on ecosystems and human health.
A single chlorine atom can destroy thousands of ozone molecules, leading to significant ozone depletion over time.
Fluorine and Other Halogens:
Though chlorine plays the primary role in ozone depletion, fluorine and bromine from halons also contribute. Bromine, in particular, is highly efficient at destroying ozone and is even more damaging than chlorine.
Impact on the Ozone Layer:
This ongoing breakdown of ozone leads to the thinning of the ozone layer, especially over the polar regions. As a result, increased amounts of ultraviolet B (UVB) radiation reach the Earth's surface, causing harmful effects on ecosystems and human health.
6.4.11 Polar stratospheric ozone depletion occurs in the spring due to the unique chemical and atmospheric conditions in the polar stratosphere.
- Explain the role of polar stratospheric clouds (PSCs) in the depletion of ozone over polar regions
- Discuss how volcanic aerosols and active surfaces contribute to ozone depletion in the polar stratosphere
Polar stratospheric ozone depletion is most severe during the spring in the polar regions, especially over Antarctica, where the phenomenon known as the ozone hole occurs. This depletion is driven by a combination of chemical and atmospheric conditions that are unique to polar environments. These conditions lead to accelerated ozone destruction, with the primary contributing factors being polar stratospheric clouds (PSCs), volcanic aerosols, and the presence of active surfaces that enhance ozone-destroying reactions.
Key Chemical and Atmospheric Conditions:
- Polar Stratospheric Clouds (PSCs):
- PSCs form during the polar winter when temperatures in the stratosphere drop below -78°C. These clouds are composed of ice crystals and nitric acid, which provide surfaces for chemical reactions that convert relatively inactive chlorine compounds (from ODSs) into highly reactive forms such as chlorine monoxide (ClO).
- When sunlight returns in the spring, these reactive chlorine compounds are released and initiate the catalytic destruction of ozone. PSCs are critical to this process because they accelerate the transformation of chlorine compounds into their active, ozone-destroying form.
- Volcanic Aerosols:
- Volcanic eruptions can inject aerosols into the stratosphere, contributing to ozone depletion by providing additional active surfaces for the chemical reactions that destroy ozone. These aerosols enhance the efficiency of chlorine and bromine reactions, further depleting the ozone layer.
- Active Surfaces:
- The cold temperatures in polar regions allow for the formation of active surfaces on PSCs and volcanic aerosols, where ozone-destroying reactions can occur. These surfaces facilitate the conversion of stable chlorine compounds into their reactive forms, significantly speeding up the rate of ozone destruction.
6.4.12 Hydrofluorocarbons (HFCs) were developed to replace CFCs as they can be used in similar ways and cause much less ozone depletion, but they are potent GHGs. They have since been controlled by the Kigali Amendment to the Montreal Protocol.
- Explain why HFCs were introduced as replacements for CFCs
- Discuss the role of the Kigali Amendment in regulating HFCs
Hydrofluorocarbons (HFCs) were developed as replacements for chlorofluorocarbons (CFCs), which were phased out under the Montreal Protocol due to their destructive impact on the ozone layer. HFCs serve similar purposes, particularly as refrigerants and in aerosols, but unlike CFCs, they do not deplete the ozone layer. However, HFCs are potent greenhouse gases (GHGs), contributing significantly to global warming. As a result, they have been regulated under the Kigali Amendment to the Montreal Protocol to reduce their emissions and mitigate their impact on climate change.
Why HFCs Replaced CFCs:
CFCs were widely used in the mid-20th century as refrigerants in refrigerators, air conditioners, and aerosols. However, due to their role in breaking down the ozone layer, their production was phased out under the Montreal Protocol. HFCs were developed as alternatives because they do not contain chlorine, making them much less harmful to the ozone layer. This made them an attractive substitute for CFCs in industries that required similar chemicals for cooling and aerosols.
Environmental Impacts of HFCs:
Kigali Amendment:
In recognition of the severe global warming potential of HFCs, the Kigali Amendment to the Montreal Protocol was adopted in 2016 to control and phase down the use of HFCs. This amendment represents a critical evolution of the Montreal Protocol, expanding its focus from just ozone depletion to addressing climate change as well. The Kigali Amendment sets a timeline for reducing HFC production and consumption, with targets for developed and developing countries to transition to less harmful alternatives.
Why HFCs Replaced CFCs:
CFCs were widely used in the mid-20th century as refrigerants in refrigerators, air conditioners, and aerosols. However, due to their role in breaking down the ozone layer, their production was phased out under the Montreal Protocol. HFCs were developed as alternatives because they do not contain chlorine, making them much less harmful to the ozone layer. This made them an attractive substitute for CFCs in industries that required similar chemicals for cooling and aerosols.
Environmental Impacts of HFCs:
- Ozone Layer: Unlike CFCs, HFCs do not contribute to ozone depletion because they lack chlorine, the key element responsible for breaking down ozone in the stratosphere.
- Greenhouse Gas Effect: Despite being ozone-friendly, HFCs are highly potent greenhouse gases, with global warming potentials (GWP) thousands of times higher than carbon dioxide (CO₂). As they are released into the atmosphere, they trap heat, significantly contributing to climate change.
Kigali Amendment:
In recognition of the severe global warming potential of HFCs, the Kigali Amendment to the Montreal Protocol was adopted in 2016 to control and phase down the use of HFCs. This amendment represents a critical evolution of the Montreal Protocol, expanding its focus from just ozone depletion to addressing climate change as well. The Kigali Amendment sets a timeline for reducing HFC production and consumption, with targets for developed and developing countries to transition to less harmful alternatives.
Leakage and Environmental Concerns:
HFCs, like CFCs, are used in appliances such as refrigerators and air conditioners. When these appliances are discarded, unless the HFCs are carefully collected and managed, they can leak into the atmosphere. These leaks contribute to the greenhouse gas effect, further amplifying the warming potential of these substances. Proper disposal and recycling of HFCs are crucial to minimize their environmental impact.
HFCs, like CFCs, are used in appliances such as refrigerators and air conditioners. When these appliances are discarded, unless the HFCs are carefully collected and managed, they can leak into the atmosphere. These leaks contribute to the greenhouse gas effect, further amplifying the warming potential of these substances. Proper disposal and recycling of HFCs are crucial to minimize their environmental impact.
6.4.13 Air conditioning units are energy-intensive, contribute to GHG emissions and traditionally have contained ODSs.
- Explain the environmental impact of air conditioning units, focusing on their contribution to greenhouse gas emissions and energy consumption.
- Discuss sustainable alternatives to air conditioning that reduce the need for artificial cooling.
Air conditioning units are widely used to regulate temperature in buildings and vehicles, but they are highly energy-intensive, leading to significant greenhouse gas (GHG) emissions. Historically, air conditioners used ozone-depleting substances (ODSs), such as chlorofluorocarbons (CFCs), as refrigerants. Although many of these substances have been phased out under the Montreal Protocol, the replacement chemicals—such as hydrofluorocarbons (HFCs)—are potent greenhouse gases. As global demand for cooling rises, addressing the environmental impact of air conditioning is crucial.
Energy Consumption and Emissions:
- Energy Use: Air conditioning accounts for a significant portion of global energy consumption, particularly in warmer climates. As buildings rely on electricity to power air conditioners, this contributes to increased demand for fossil fuel energy, which in turn raises CO₂ emissions and exacerbates climate change.
- Greenhouse Gas Emissions: Older air conditioning systems used CFCs, which depleted the ozone layer, while newer systems often use HFCs, which, while ozone-friendly, have high global warming potential (GWP). These emissions contribute significantly to global warming, making the need for alternatives critical.
Development of Substitute Refrigerants:
To mitigate the environmental impact of refrigerants, new alternatives are being developed that are less harmful to both the ozone layer and the climate. These include:
- Natural Refrigerants: Substitutes like hydrocarbons (HCs), ammonia (NH₃), and carbon dioxide (CO₂) have been developed as refrigerants that have minimal ozone-depleting potential and low global warming potential.
- Hydrofluoroolefins (HFOs): HFOs are synthetic refrigerants with a much lower GWP compared to HFCs and are increasingly being adopted in cooling technologies as a more environmentally friendly option.
Sustainable Alternatives to Air Conditioning:
In addition to improving refrigerants, other sustainable alternatives to reduce the energy demand and environmental impact of air conditioning include:
- Improved Building Design:
- Passive Cooling: Incorporating architectural designs that minimize heat gain, such as proper insulation, reflective roofs, and energy-efficient windows, can reduce the need for artificial cooling.
- Natural Ventilation: Designing buildings to maximize natural airflow can reduce reliance on mechanical cooling systems.
- Greening and Rewilding of Cities:
- Urban Greening: Planting trees and creating green spaces in cities helps reduce the urban heat island effect (where cities are significantly warmer than surrounding rural areas due to concrete and asphalt absorbing heat). Trees and plants provide shade and cool the air through evapotranspiration.
- Green Roofs and Walls: These features insulate buildings and help to cool the environment by absorbing heat and providing natural cooling.
- Rewilding: Rewilding urban areas—restoring natural landscapes—can help to reduce the overall temperature of cities, making them less reliant on air conditioning.
Activity Research the use of air-conditioners in your home country or another country of your choice.
Activity: Research the use of alternatives to air conditioning units. Use databases to collect data on the use of air conditioning units in different societies and present this data graphically, considering the reasons for the differences per capita.
Key Terms
|
Ozone Layer
Ultraviolet Radiation (UV) UVB and UVC Ozone Depletion Ozone-Depleting Substances (ODSs) HL ONLY Catalytic Destruction Chlorine Bromine Polar Ozone Depletion Hydrofluorocarbons (HFCs) Kigali Amendment Volcanic Aerosols Energy Efficiency Urban Greening Natural Refrigerants GHG Emissions from Air Conditioning Passive Cooling |
Gas-blown plastics
Chlorofluorocarbon Skin Cancer Stratosphere |
Polar Stratospheric Clouds (PSCs)
Halogenated organic gases Electromagnetic Spectrum Montreal Protocol Shortwave radiation |
Classroom Materials
| Subtopic 6.4 Stratospheric Ozone Presentation..pptx |
| Subtopic 6.4 Stratospheric Ozone Workbook.docx |
Monitoring Tropospheric Ozone Lab
The Ozone Layer Lab
Montreal Protocol Case Study
Montreal Protocol article
Ozone depletion vs Global Warming
Our World Data Ozone Database
Case Study
- One detailed case study evaluating the role of national and international organizations in reducing the emissions of ozone-depleting substances (eg. the Montreal Protocol)
Ozone Case Study
Correct use of terminology is a key skill in ESS. It is essential to use key terms correctly when communicating your understanding, particularly in assessments. Use the quizlet flashcards or other tools such as learn, scatter, space race, speller and test to help you master the vocabulary.
Useful Links
Ozone formation and destruction, as well as its link to global warming - Dynamic Science
Ozone - EPA
NASA’s Earth Observatory page on tropospheric ozone - NASA
Webster’s Online Dictionary entry for ozone
Tropospheric ozone processes. - Belgium Institute of Space Aeronomy
Health Effect of UV radiation - WHO
Positive and Negative Effects of UV Radiation - Science Learn
Convention on Long-Range Transboundary Air Pollution (LRTAP), Geneva, 1979 - Wikipedia
Vienna Convention for the Protection of the Ozone Layer, Vienna, 1985 - Wikipedia
Montreal Protocol on Substances that Deplete the Ozone Layer, Montreal 1987 - Wikipedia
Ozone formation and destruction, as well as its link to global warming - Dynamic Science
Ozone - EPA
NASA’s Earth Observatory page on tropospheric ozone - NASA
Webster’s Online Dictionary entry for ozone
Tropospheric ozone processes. - Belgium Institute of Space Aeronomy
Health Effect of UV radiation - WHO
Positive and Negative Effects of UV Radiation - Science Learn
Convention on Long-Range Transboundary Air Pollution (LRTAP), Geneva, 1979 - Wikipedia
Vienna Convention for the Protection of the Ozone Layer, Vienna, 1985 - Wikipedia
Montreal Protocol on Substances that Deplete the Ozone Layer, Montreal 1987 - Wikipedia
In The News
Nations, Fighting Powerful Refrigerant That Warms Planet, Reach Landmark Deal - New York Times October 2016
Greenhouse gases deal will make little difference to west - Guardian Oct 2016
Ozone depletion: SA to phase out harmful gases but struggles to find suitable alternatives - Traveller24 Oct 2016
Ozone Hole Shows Signs of Shrinking, Scientists Say - New York Times Jun 2016
Ultraviolet Radiation: How It Affects Life on Earth - NASA · September 6, 2001
Nations, Fighting Powerful Refrigerant That Warms Planet, Reach Landmark Deal - New York Times October 2016
Greenhouse gases deal will make little difference to west - Guardian Oct 2016
Ozone depletion: SA to phase out harmful gases but struggles to find suitable alternatives - Traveller24 Oct 2016
Ozone Hole Shows Signs of Shrinking, Scientists Say - New York Times Jun 2016
Ultraviolet Radiation: How It Affects Life on Earth - NASA · September 6, 2001
International-mindedness:
- The depletion of ozone has global implications to ocean productivity and oxygen production.
- National economic approaches may have an impact on international environmental discussions.
TOK
- The Montreal Protocol was an international agreement created by the UN—can one group or organization decide what is best for the rest of the world?
Video Clips
CFCs and Ozone
NASA's been tracking the thinning of the ozone layer the south pole for nearly 20 years. In this slowed-down animation, you can watch the ozone hole's average size each October.
Restrictions on chemicals credited in ozone-hole shrinkage
The signing of the Montreal Protocol in September 1987 launched an unprecedented global effort in the protection of the environment. To this day, the Vienna Convention and the Montreal Protocol are the only universally ratified treaties, uniting 198 countries in taking on the fight against man-made ozone depleting substances.
