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• Depletion of Ozone Layer Essay

Essay on Depletion of Ozone Layer

The essay on ozone layer depletion and protection gives us insight into changes in our environment. Ozone is super-charged oxygen in the lower level of the stratosphere. It makes a layer in the air, which goes about as a spread to the Earth against the bright radiation of the Sun. The ozone layer's shelter is with a variable degree less thick close to the outside of the Earth contrasted with the tallness of 30km. This depletion of Ozone layer essay explains the causes and effects of its depletion.

Ozone Layer Depletion

Ozone layer consumption is the diminishing of the ozone layer present in the upper air. This happens when the chlorine and bromine iotas in the environment interact with ozone and crush the ozone atoms. One chlorine can pulverize 100,000 atoms of ozone. It is devastated more rapidly than it is made. A few mixes discharge chlorine and bromine on presentation to high bright light, which at that point adds to the ozone layer consumption. Such mixes are known as Ozone Depleting Substances.

This essay on ozone layer in English states the most important causes of ozone depletion. A few contaminations in the environment like chlorofluorocarbons (CH 3 ) cause the exhaustion of the ozone layer. These CFCs and other comparable gases, when reaching the stratosphere they are separated by the bright radiation, and accordingly, the free particles of chlorine or bromine. These molecules are profoundly responsive to ozone and disturb stratospheric science. The responses drain the ozone layer. Researchers state that the unregulated dispatching of rockets brings about substantially more exhaustion of the ozone layer than the CFCs do. If not controlled, this may bring about a tremendous loss of the ozone layer constantly by 2050.

The depletion of ozone layer essay also provides the following effects of the depletion. Because of the consumption of the ozone layer, the Earth is presented to ultra-disregard radiation. These beams cause a harmful impact on living creatures on the Earth. It influences the cycle of photosynthesis in plants. Ascend in the temperature, different skin infections, a decline of invulnerability, and so forth are the plausible outcomes. Direct presentation to bright radiations prompts skin and eye malignant growth in creatures. Tiny fishes are incredibly influenced by the introduction to destructive bright beams. These are higher in the amphibian natural way of life.

The greater part of the cleaning items has chlorine and bromine, delivering synthetics that discover a route into the air and influence the ozone layer. These ought to be subbed with common items to secure the climate. The vehicles produce a lot of ozone-depleting substances that lead to a dangerous atmospheric deviation, just as ozone consumption. Along these lines, vehicles' utilization ought to be limited, however much as could be expected. Normal techniques ought to be actualized to dispose of bugs and weeds as opposed to utilizing synthetics. One can utilize eco-accommodating synthetic compounds to eliminate the nuisances or eliminate the weeds physically.

For the security of the ozone layer, the Vienna Conference in March 1985 was held. In September 1987, the Montreal Protocol was agreed upon. This was followed by the Kyoto Protocol of 1997. Under the Protocol, 37 nations invest in a decrease of four GreenHouse Gases and two gatherings of gases delivered by them, and all part nations give general responsibilities.

Prevention of the Depletion of the Ozone Layer

Ozone layer depletion can be avoided by first understanding the root of the problem. This means that first, the students have to understand what causes ozone layer depletion and then reduce those practices as much as possible. One of the reasons why ozone depletion happens is because of the increased production of chlorofluorocarbons. These are present in many things around us such as in solvents, refrigerators, air conditioners, etc. 

The ozone layer also gets depleted due to Nitrogenous compounds such as NO 2 , NO, N 2 O. One other reason for ozone layer depletion are the natural causes or processes such as Sun-spots etc but this cannot be considered as one of the main reasons for the depletion in the Ozone layer because the only harm it does is 1-2 percent. Some other examples of the things which deplete the Ozone layer are natural volcanoes. So, the methods to prevent Ozone layer Depletion are avoiding the use of Ozone-depleting substances which include, CFCs in refrigerators etc or avoiding using private means of transport and using public transports as much as possible or trying using bicycle or walking which is an environmentally friendly solution. Also, the students should note that replacing eco-friendly substances at the place of chlorine, bromine or other harmful releasing products helps in the prevention of ozone layer depletion.

The essay on depletion of the ozone layer tells us about the harmful effects of it and ways to combat it. This ozone layer depletion essay in English helps us recognize its cause and provides us with insight into how to stop them.

FAQs on Depletion of Ozone Layer Essay

1. What is the Ozone Layer?

Ozone has been the most receptive type of sub-atomic oxygen and the fourth most impressive oxidizing specialist. It has a wonderful focus at around 2 ppm or less. However, higher fixation is aggravating. It is utilized as a disinfectant and blanching operator. In nature, O 3 is framed in the stratosphere when bright light strikes an oxygen particle. A photon parts the oxygen particle into two profoundly receptive oxygen atoms(O). These consolidate rapidly with an oxygen particle to shape ozone. The O 3 promptly retains UV light and separates into its constituent segments.

2. Where is the Ozone Hole found?

One instance of ozone depletion is the yearly ozone hole over Antarctica that has been continuously on-going during the Antarctic spring, since the mid-1980s. This isn't generally a gap through the ozone layer, yet rather a huge territory of the stratosphere with incredibly low ozone measures. Understand that ozone exhaustion isn't restricted to the zone over the South Pole. Exploration has indicated that ozone consumption happens over the scopes that incorporate North America, Europe, Asia, and quite a bit of Africa, Australia, and South America. In the 19th century, the ozone hole has extended to every continent.

3. Where can I find a well-written essay on the Depletion of the Ozone Layer?

Students can easily find a well-written essay on the Depletion of the Ozone layer at Vedantu. The essay is informative and easy to understand because of the proper usage of simple words. There are various other essays available also in the Vedantu app which are easily available to the students for their better preparation for any examinations or competitions which they may be expecting. To find more such essays sign in at Vedantu via our website or app and read an essay of your choice.

4.  Are there any harmful effects due to the Depletion of the Ozone layer?

There are numerous harmful effects of Ozone layer depletion. Some of them are increased temperature of the planet earth, variants of skin infections, eye problems, a faster rate of aging, Cancer, reduction in the rate of flowering plants and so much more. The students must know that it is very important to avoid this from happening or the results will be disastrous. Hence, they must educate themselves by learning about the causes of these effects and how to reduce them for a better world.

5. Why should I study the Depletion of the Ozone layer?

The students should know about the study of the Ozone layer as this is what affects the climate indirectly and directly. One must take the appropriate measures to do everything they possibly can in order to make sure that they are doing their due for the climate and the planet earth. There should be various meetings, events and other group-based activities which educate people about the importance of the Ozone layer and why its depletion should be avoided at all costs. The students should also take the matters into their own hands to make sure that the people around them are not causing any excessive damage or adding to the reasons for the depletion of the ozone layer. This can only be made sure if the institutions educate the students on the various environmental topics and how the students can make a difference. Teachers and schools are also responsible in many ways to present the students with these topics which are later on helpful in life. This is why it is important for the essays in English to be about the various informative things which are needed in real life. Thus, it is important that every student understands the essay about the depletion of the ozone layer as it not only helps them to write in English smoothly but also makes sure they are getting educated through the various topics aforementioned. Thus, make sure that you read the essay on the depletion of the ozone layer as it is not only a theoretical scientific topic but also helps in enhancing one’s writing skills.

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The Ozone Layer

Ozone (O 3 ) is a gaseous molecule that occurs in different parts of the atmosphere (Figure 1). It is chemically reactive and is dangerous to plant and animal life when present in the lower portions of the atmosphere. This type of ozone, called ground-level ozone , is a significant hazard to human health and is associated with pollution from vehicle exhaust and other anthropogenic emissions (see section 10.1 ).

Ozone in the upper atmosphere is naturally occurring and beneficial to life because it blocks harmful radiation from the sun. This type of ozone is called stratospheric ozone . Ozone in the stratosphere (Figure 2) forms when the energy of sunlight breaks apart the two oxygen atoms in an O2 molecule. Each lone oxygen atom can then combine with a different O 2 molecule to form O 3 , ozone. The ozone layer is the portion of the stratosphere where ozone molecules are present, mixed in among the other gases that comprise the atmosphere (Figure 2).

Radiation from the sun is also called electromagnetic radiation or simply referred to as light. The sun emits different types of light, including but not limited to x-rays, visible light, microwaves, and ultraviolet light. The various types of light are distinguished by their different wavelengths. As the wavelength decreases, the amount of energy in that light increases. Ultraviolet light , for example, has shorter wavelengths than visible light and is thus more energetic. Ozone molecules absorb ultraviolet (UV) light, which is advantageous for life on Earth because UV light can break down important biomolecules such as DNA, leading to cell death and mutations.

Ozone Depletion

Unfortunately, the ozone layer that protects life on Earth from harmful UV light has been depleted due to human activities. The ozone depletion process begins when  CFCs (chlorofluorocarbons) and other  ozone-depleting substances (ODS) are emitted into the atmosphere. The industry used CFCs as refrigerants, degreasing solvents, and propellants. In the lower atmosphere, CFC molecules are extremely stable chemically and do not dissolve in the rain, and thus can linger for long periods. After several years, ODS molecules eventually reach the ozone layer in the stratosphere, starting about 10 kilometers above the Earth’s surface.

Once in the stratosphere, CFCs and other ODS destroy ozone molecules. In the case of CFCs, UV light in the stratosphere knocks loose a chlorine atom from the molecule, which can then destroy numerous ozone molecules, as shown in Figure 3. In effect, ODS are removing ozone faster than it is created by natural processes (as described above), leading to a thinning of the ozone layer. This thinning represents a reduction in the concentration of ozone molecules in a particular portion of the stratosphere. Areas, where the ozone layer has thinned are commonly called holes. However, this is not entirely accurate because ozone is still present; it just exists at concentrations much lower than normal.

Policies to Reduce Ozone Destruction

Tackling the issue of ozone layer destruction is an example of global cooperation that produced meaningful action on a large-scale environmental problem. In 1973, scientists first calculated that CFCs could reach the stratosphere and destroy ozone. Based only on their calculations, the United States and most Scandinavian countries banned CFCs in spray cans in 1978.

But more confirmation that CFCs break down ozone was needed before additional action was taken. In 1985, members of the British Antarctic Survey reported that a 50% reduction in the ozone layer had been found over Antarctica in the previous three springs, a very important finding.

Two years after that seminal British Antarctic Survey report, an agreement titled the “Montreal Protocol on Substances that Deplete the Ozone Layer” was ratified by nations worldwide. The Montreal Protocol, as it is commonly called, controls the production and emission of 96 chemicals that damage the ozone layer. As a result, CFCs have been mostly phased out since 1995, although they were used in developing nations until 2010. Some of the less hazardous substances will not be phased out until 2030. The Montreal Protocol also requires that wealthier nations donate money to develop technologies that will replace these chemicals.

The Montreal Protocol was a success, and scientists have found that the ozone layer is recovering and the size of the ozone “holes” are shrinking, thanks to a drastic reduction in the emission of ODS like CFCs. However, the recovery process is slow because CFCs take many years to reach the stratosphere and can survive there a long time before they break down and are rendered harmless. Thus, the ozone layer will take many more decades to recover fully.

However, constant vigilance and monitoring are needed as illegal production and emission of CFCs and other ODS threaten recovery efforts. In 2018, scientists from the US National Oceanic and Atmospheric Administration reported that emissions of a particular type of CFC had increased 25% since 2012. Follow-up studies have since approximated the emissions originating in particular regions of eastern Asia.

Health and Environmental Effects of Ozone Layer Depletion

There are three types of UV light, each distinguished by their wavelengths: UV-A, UV-B, and UV-C. Stratospheric ozone molecules absorb the sun’s UV-C light and most of its UV-B light (Figure 5).

Reductions in stratospheric ozone levels led to higher levels of UV-B reaching the Earth’s surface, which is a serious hazard to human health. Studies have shown that in the Antarctic, the amount of UV-B measured at the surface can double due to thinning of the ozone layer. UV-B harms cells because it can interact with biomolecules like DNA and damage them. This can lead to mutations and cell death. UV-B cannot penetrate multicellular organisms very far and thus tends only to affect cells near the surface, such as in the skin of animals. Microbes like bacteria, however, are composed of only one cell and can therefore be killed by UV-B.

Laboratory and epidemiological studies demonstrate that UV-B causes certain types of skin cancers in humans and plays a major role in developing malignant melanoma (a particularly dangerous form of skin cancer). In addition, UV-B causes cataracts, a clouding of the lens in the eye that can lead to poor vision or even blindness.

It is important to note that all sunlight contains some UV-B light, even with normal stratospheric ozone levels. Therefore, protecting your skin and eyes from the sun is important. Ozone layer depletion increases the amount of UV-B and the risk of health effects.

Introduction to Environmental Sciences and Sustainability Copyright © 2023 by Emily P. Harris is licensed under a Creative Commons Attribution 4.0 International License , except where otherwise noted.

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• ENVIRONMENT

What is the ozone layer, and why does it matter?

Human activity has damaged this protective layer of the stratosphere, but scientists say the ozone layer is on track for recovery.

Earth's ozone layer, an early symbol of global environmental degradation, is improving and on track to recover by the middle of the 21st century.  

Over the past 30 years, humans have successfully phased out many of the chemicals that harm the ozone layer , the atmospheric shield that sits in the stratosphere about nine to 18 miles (15 to 30 kilometers) above Earth's surface.

Atmospheric ozone absorbs ultraviolet (UV) radiation from the sun, particularly harmful UVB-type rays. Exposure to UVB radiation is linked with increased risk of skin cancer and cataracts, as well as damage to plants and marine ecosystems. Atmospheric ozone is sometimes labeled as the "good" ozone, because of its protective role, and shouldn't be confused with tropospheric, or ground-level, "bad" ozone, a key component of air pollution that is linked with respiratory disease.

( See where air pollution is lethal. )

Ozone (O3) is a highly reactive gas whose molecules are comprised of three oxygen atoms. Its concentration in the atmosphere naturally fluctuates depending on seasons and latitudes, but it was generally stable when global measurements began in 1957 .  

Groundbreaking research in the 1970s and 1980s revealed signs of trouble.

Ozone threats and 'the hole'

In 1974, Mario Molina and Sherwood Rowland, two chemists at the University of California, Irvine, published an article in the journal Nature detailing threats to the ozone layer from chlorofluorocarbon (CFC) gases. At the time, CFCs were commonly used in aerosol sprays and as coolants in many refrigerators. As they reach the stratosphere, the sun's UV rays break CFCs down into substances such as chlorine.

This groundbreaking research—for which they were awarded the 1995 Nobel Prize in chemistry —concluded that the atmosphere had a “finite capacity for absorbing chlorine” atoms in the stratosphere.

One atom of chlorine can destroy more than 100,000 ozone molecules, according to the U.S. Environmental Protection Agency , eradicating ozone much more quickly than it can be replaced.

Molina and Rowland’s study was validated in 1985, when a team of English scientists found a hole in the ozone layer over Antarctica that was later linked to CFCs. The "hole" is actually an area of the stratosphere with extremely low concentrations of ozone that reoccurs every year at the beginning of the Southern Hemisphere spring (August to October).

At the North Pole, a degraded ozone layer is responsible for the Arctic's rapid rate of warming, according to a 2020 study published in Nature Climate Change . CFCs are a more potent greenhouse gas than carbon dioxide, the most abundant planet-warming gas.  

Aerosol from cans sometimes contains ozone-depleting substances called chlorofluorocarbons, or CFCs.

The ozone layer’s status today

In a report released in early 2023 , scientists keeping track of the ozone layer noted that Earth's atmosphere is recovering. The ozone layer will be restored to its 1980 condition—before the ozone hole emerged—by 2040. More persistent ozone holes over the Arctic and Antarctica should recover by 2045 and 2066, respectively.  

This progress is thanks to the Montreal Protocol on Substances That Deplete the Ozone Layer , a landmark agreement signed by 197 UN member countries in 1987 to phase out ozone-depleting substances. Without the pact, the EPA estimates the U.S. would have seen an additional 280 million cases of skin cancer, 1.5 million skin cancer deaths, and 45 million cataracts—and the world would be at least 25 percent hotter.

( Read more about how climate change is a threat to human health. )

Nearly all the ozone-destroying chemicals banned by the Montreal Protocol have been phased out, but some harmful gases are still used. Hydrochlorofluorocarbons (HCFCs), transitional substitutes that are less damaging but still harmful to ozone, are still in use in some countries. HCFCs are also powerful greenhouse gases that trap heat and contribute to climate change .

Though HFCs represent a small fraction of emissions compared with carbon dioxide and other greenhouse gases , their planet-warming effect prompted an addition to the Montreal Protocol, the Kigali Amendment , in 2016. The amendment, which came into force in January 2019, aims to slash the use of HFCs by more than 80 percent over the next three decades.  

In the meantime, companies and scientists are working on climate-friendly alternatives, including new coolants and technologies that reduce or eliminate dependence on chemicals altogether.

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• Environmental Chemistry
• Effects Of Ozone Layer Depletion

Effects of Ozone Layer Depletion

What is ozone layer depletion.

The ozone layer present in the stratosphere acts as a protective shield. It saves the earth from the harmful ultraviolet rays of the sun. The compounds containing CFCs (chlorofluorocarbons) are mainly responsible for ozone layer depletion as these compounds react with ozone in the presence of ultraviolet rays to form oxygen molecules and thus, destroying ozone.

Scientists have already found an ozone hole over the South Pole. Once the ozone layer is depleted, ultraviolet rays will pass through the troposphere and eventually to earth. These rays cause ageing of the skin, skin cancer, cataract and sunburn to humans as well as animals. Phytoplankton dies in the presence of ultraviolet rays which results in a decrease in fish productivity.

Ozone Layer Depletion

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Causes & Effects of Ozone Layer Depletion

The evaporation of surface water through the stomata of leaves increases, which results in the decreased moisture content of the soil. The proteins cells in plants undergo harmful mutations, all due to ultraviolet radiation. Paints and fibres are also damaged by the increased levels of ultraviolet rays, causing them to fade faster.

Chlorofluorocarbons and other halocarbons are held responsible for ozone layer depletion, but if we explore more about them we will find that these are major greenhouse gases . These gases absorb heat in the atmosphere and increase the earth’s temperature, resulting in global warming. Increase in earth’s temperature causes the melting of ice caps. This raises the water level of the oceans and seas. Coastal areas get flooded and area under land cover reduces.

The Ozone Hole

In the year 1980 scientists reported the depletion of the ozone layer in the region of Antarctica which is commonly known as the ozone hole. Ozone layer depletion occurs due to unique sets of climatic conditions. In the summer, nitrogen dioxide and methane react with chlorine monoxide and chlorine atoms which results in a shrinkage of chlorine and hence prevents ozone layer depletion.

ClO (g) + NO 2 (g) → ClONO 2 (g)

Cl (g) + CH 4 (g) → CH 3 (g) + HCl (g)

During winter, special types of clouds are formed over the Antarctic region. These clouds provide the surface for the hydrolysis of chlorine nitrate to form hypochlorous acid. Chlorine nitrate also reacts with hydrogen chloride thereby producing molecular chlorine .

ClONO 2 (g) + H 2 O (g) → HOCl (g) + HNO 3 (g)

ClONO 2 (g) + HCl (g) → Cl 2 (g) + HNO 3 (g)

During spring, sunlight enters Antarctica and breaks up the clouds. Photolysis of HOCl and Cl 2 occurs which forms chlorine radicals and this reaction initiates the ozone layer depletion.

Prevention and Measures

Many plants and animals find it difficult to survive in areas having a high temperatures. In such cases, the changes in climatic conditions are the main reason for their extinction. The following measures should be taken to prevent the ozone layer depletion:

• Private vehicle driving should be limited – Vehicular emission results in smog, which harms the ozone layer. Carpooling, using public modes of transportation, walking, cycling etc should be promoted.
• Avoid using pesticides – Pesticides are used for getting rid of weeds but are very harmful to the ozone layer. Natural remedies should be used instead of pesticides.
• Using eco-friendly products – We can use eco-friendly cleaning products for domestic purposes and save the ozone from further deterioration.
• Replacing CFC’s used in air conditioners and refrigerators – Hydrofluorocarbons (HFCs) have been identified as potential replacements for CFCs (which is the major cause of Ozone Layer Depletion) as they have an Ozone Depletion Potential of 0. The use of HFCs in place of CFCs will go a long way in protecting our Ozone layer from getting depleted.
• Proper Waste disposal techniques –  Avoid burning waste materials like plastic and other materials. Give non-decomposable products for recycling or try and reuse them for other purposes.

We have seen the various effects of ozone layer depletion and can conclude by saying that it is very important for our survival. Measures should be taken to protect our earth from harmful ultraviolet rays. This can only be done by reducing the use of compounds which react in the atmosphere to harm the ozone layer.

Frequently Asked Questions – FAQs

What is ozone layer depletion how does it occur, what are ozone-depleting substances give examples., what is the main aim of the montreal protocol, what are the effects of ozone layer depletion on human health.

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• Published: 24 June 2019

Ozone depletion, ultraviolet radiation, climate change and prospects for a sustainable future

• Paul W. Barnes   ORCID: orcid.org/0000-0002-5715-3679 1   na1 ,
• Craig E. Williamson 2   na1 ,
• Robyn M. Lucas   ORCID: orcid.org/0000-0003-2736-3541 3   na1 ,
• Sharon A. Robinson   ORCID: orcid.org/0000-0002-7130-9617 4   na1 ,
• Sasha Madronich 5   na1 ,
• Nigel D. Paul 6   na1 ,
• Janet F. Bornman 7 ,
• Alkiviadis F. Bais 8 ,
• Barbara Sulzberger 9 ,
• Stephen R. Wilson 10 ,
• Anthony L. Andrady 11 ,
• Richard L. McKenzie 12 ,
• Patrick J. Neale 13 ,
• Amy T. Austin 14 ,
• Germar H. Bernhard 15 ,
• Keith R. Solomon   ORCID: orcid.org/0000-0002-8496-6413 16 ,
• Rachel E. Neale 17 ,
• Paul J. Young 6 ,
• Mary Norval 18 ,
• Lesley E. Rhodes 19 ,
• Samuel Hylander 20 ,
• Kevin C. Rose 21 ,
• Janice Longstreth 22 ,
• Pieter J. Aucamp 23 ,
• Carlos L. Ballaré 14 ,
• Rose M. Cory 24 ,
• Stephan D. Flint 25 ,
• Frank R. de Gruijl 26 ,
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• Anu M. Heikkilä 28 ,
• Marcel A. K. Jansen 29 ,
• Krishna K. Pandey 30 ,
• T. Matthew Robson 31 ,
• Craig A. Sinclair 32 ,
• Sten-Åke Wängberg 33 ,
• Robert C. Worrest 34 ,
• Seyhan Yazar 35 ,
• Antony R. Young 36 &
• Richard G. Zepp 37  

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• Environmental health

Changes in stratospheric ozone and climate over the past 40-plus years have altered the solar ultraviolet (UV) radiation conditions at the Earth’s surface. Ozone depletion has also contributed to climate change across the Southern Hemisphere. These changes are interacting in complex ways to affect human health, food and water security, and ecosystem services. Many adverse effects of high UV exposure have been avoided thanks to the Montreal Protocol with its Amendments and Adjustments, which have effectively controlled the production and use of ozone-depleting substances. This international treaty has also played an important role in mitigating climate change. Climate change is modifying UV exposure and affecting how people and ecosystems respond to UV; these effects will become more pronounced in the future. The interactions between stratospheric ozone, climate and UV radiation will therefore shift over time; however, the Montreal Protocol will continue to have far-reaching benefits for human well-being and environmental sustainability.

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Crutzen, P. J. The influence of nitrogen oxides on the atmospheric ozone content. Q. J. Royal Meteorol. Soc. 96 , 320–325 (1970).

Article   Google Scholar  

Molina, M. J. & Rowland, F. S. Stratospheric sink for chlorofluoromethanes: chlorine atomic-catalysed destruction of ozone. Nature 249 , 810–812 (1974).

Article   CAS   Google Scholar  

Farman, J. C., Gardiner, B. G. & Shanklin, J. D. Large losses of ozone in Antarctica reveal seasonal ClO x /NO x interaction. Nature 315 , 207–210 (1985).

Watson, R. T., Prather, M. J. & Kurylo, M. J. Present State of Knowledge of the Upper Atmosphere 1988: An Assessment Report . NASA Reference Publication 1208 (NASA Office of Space Science and Applications, 1988).

Synthesis Report: Integration of the Four Assessment Panels Reports by the Open-Ended Working Group of the Parties to the Montreal Protocol (OEWG, 1989).

Solomon, S., Garcia, R. R., Rowland, F. S. & Wuebbles, D. J. On the depletion of Antarctic ozone. Nature 321 , 755–758 (1986).

Solomon, S. Progress towards a quantitative understanding of Antarctic ozone depletion. Nature 347 , 347–354 (1990).

Andersen, S. O. & Sarma, K. M. Protecting the Ozone Layer: The United Nations History (Earthscan, 2012).

Newman, P. A. et al. What would have happened to the ozone layer if chlorofluorocarbons (CFCs) had not been regulated? Atmos. Chem. Phys. 9 , 2113–2128 (2009).

Mäder, J. A. et al. Evidence for the effectiveness of the Montreal Protocol to protect the ozone layer. Atmos. Chem. Phys. 10 , 12161–12171 (2010).

Newman, P. A. & McKenzie, R. UV impacts avoided by the Montreal Protocol. Photochem. Photobiol. Sci. 10 , 1152–1160 (2011).

S cientific Assessment of Ozone Depletion: 2018, Global Ozone Research and Monitoring Project . Report no. 58.88 (WMO, 2018).

Updating Ozone Calculations and Emissions Profiles for Use in the Atmospheric and Health Effects Framework Model (USEPA, 2015).

Myhre, G. et al. in IPCC Climate Change 2013: The Physical Science Basis (eds Stocker, T. F. et al.) 661–740 (Cambridge Univ. Press, 2013).

Garcia, R. R., Kinnison, D. E. & Marsh, D. R. ‘World Avoided’ simulations with the Whole Atmosphere Community Climate Model. J. Geophys. Res. Atm . 117 , D23303 (2012).

Google Scholar  

Ripley, K. & Verkuijl, C. ‘Ozone family’ delivers landmark deal for the climate. Environ . Policy Law 46 , 371 (2016).

Xu, Y., Zaelke, D., Velders, G. J. M. & Ramanathan, V. The role of HFCs in mitigating 21st century climate change. Atmos. Chem. Phys. 13 , 6083–6089 (2013).

Chipperfield, M. P. et al. Quantifying the ozone and ultraviolet benefits already achieved by the Montreal Protocol. Nat. Commun. 6 , 7233 (2015).

Velders, G. J., Andersen, S. O., Daniel, J. S., Fahey, D. W. & McFarland, M. The importance of the Montreal Protocol in protecting climate. Proc. Natl Acad.Sci. USA 104 , 4814–4819 (2007).

Papanastasiou, D. K., Beltrone, A., Marshall, P. & Burkholder, J. B. Global warming potential estimates for the C 1 –C 3 hydrochlorofluorocarbons (HCFCs) included in the Kigali Amendment to the Montreal Protocol. Atmos. Chem. Phys. 18 , 6317–6330 (2018).

IPCC: Summary for Policymakers. In Global Warming of 1.5 °C . IPCC Special Report (IPCC, 2018).

Andrady, A. L., Pandey, K. K. & Heikkilä, A. M. Interactive effects of solar UV radiation and climate change on material damage. Photochem. Photobiol. Sci. 18 , 804–825 (2019).

Lucas, R. M. et al. Human health in relation to exposure to solar ultraviolet radiation under changing stratospheric ozone and climate. Photochem. Photobiol. Sci. 18 , 641–680 (2019).

Bornman, J. F. et al. Linkages between stratospheric ozone, UV radiation and climate change and their implications for terrestrial ecosystems. Photochem. Photobiol. Sci. 18 , 681–716 (2019).

Williamson, C. E. et al. The interactive effects of stratospheric ozone depletion, UV radiation, and climate change on aquatic ecosystems. Photochem. Photobiol. Sci. 18 , 717–746 (2019).

Sulzberger, B., Austin, A. T., Cory, R. M., Zepp, R. G. & Paul, N. D. Solar UV radiation in a changing world: roles of cryosphere–land–water–atmosphere interfaces in global biogeochemical cycles. Photochem. Photobiol. Sci. 18 , 747–774 (2019).

Bais, A. F. et al. Ozone–climate interactions and effects on solar ultraviolet radiation. Photochem. Photobiol. Sci. 18 , 602–640 (2019).

Wilson, S. R., Madronich, S., Longstreth, J. D. & Solomon, K. R. Interactive effects of changing stratospheric ozone and climate on composition of the troposphere, air quality, and consequences for human and ecosystem health. Photochem. Photobiol. Sci. 18 , 775–803 (2019).

IPCC Climate Change 2014: Synthesis Report (eds Core Writing Team, Pachauri, R. K. & Meyer L. A.) (IPCC, 2014).

Arblaster, J. et al. In Scientific Assessment of Ozone Depletion: 2014. Global Ozone Research and Monitoring Project Report No. 55, Ch. 4 (WMO, 2014).

Langematz, U. et al. In Scientific Assessment of Ozone Depletion: 2018. Global Ozone Research and Monitoring Project Report No. 58, Ch. 4 (WMO, 2018).

Clem, K. R., Renwick, J. A. & McGregor, J. Relationship between eastern tropical Pacific cooling and recent trends in the Southern Hemisphere zonal-mean circulation. Clim. Dyn. 49 , 113–129 (2017).

Lim, E. P. et al. The impact of the Southern Annular Mode on future changes in Southern Hemisphere rainfall. Geophys. Res. Lett. 43 , 7160–7167 (2016).

Holz, A. et al. Southern Annular Mode drives multicentury wildfire activity in southern South America. Proc. Natl Acad. Sci. USA 114 , 9552–9557 (2017).

Kostov, Y. et al. Fast and slow responses of Southern Ocean sea surface temperature to SAM in coupled climate models. Clim. Dyn. 48 , 1595–1609 (2017).

Oliveira, F. N. M. & Ambrizzi, T. The effects of ENSO-types and SAM on the large-scale southern blockings. Int. J. Climatol. 37 , 3067–3081 (2017).

Robinson, S. A. et al. Rapid change in East Antarctic terrestrial vegetation in response to regional drying. Nat. Clim. Change 8 , 879–884 (2018).

Robinson, S. A. & Erickson, D. J. III Not just about sunburn—the ozone hole’s profound effect on climate has significant implications for Southern Hemisphere ecosystems. Glob. Change Biol. 21 , 515–527 (2015).

Morgenstern, O. et al. Review of the global models used within phase 1 of the Chemistry–Climate Model Initiative (CCMI). Geosci. Model Dev. 10 , 639–671 (2017).

Williamson, C. E. et al. Solar ultraviolet radiation in a changing climate. Nat. Clim. Change 4 , 434–441 (2014).

IPCC Climate Change 2013: The Physical Science Basis (eds Stocker, T. F. et al.) (Cambridge Univ. Press, 2013).

López, M. L., Palancar, G. G. & Toselli, B. M. Effects of stratocumulus, cumulus, and cirrus clouds on the UV-B diffuse to global ratio: experimental and modeling results. J. Quant. Spectrosc. Radiat. Transf. 113 , 461–469 (2012).

Feister, U., Cabrol, N. & Häder, D. UV irradiance enhancements by scattering of solar radiation from clouds. Atmosphere 6 , 1211–1228 (2015).

Williamson, C. E. et al. Sentinel responses to droughts, wildfires, and floods: effects of UV radiation on lakes and their ecosystem services. Front. Ecol. Environ. 14 , 102–109 (2016).

Gies, P., Roy, C., Toomey, S. & Tomlinson, D. Ambient solar UVR, personal exposure and protection. J. Epidemiol. 9 , S115–S122 (1999).

Xiang, F. et al. Weekend personal ultraviolet radiation exposure in four cities in Australia: influence of temperature, humidity and ambient ultraviolet radiation. J. Photochem. Photobiol. B 143 , 74–81 (2015).

Cuthill, I. C. et al. The biology of color. Science 357 , eaan0221 (2017).

Mazza, C. A., Izaguirre, M. M., Curiale, J. & Ballaré, C. L. A look into the invisible. Ultraviolet-B sensitivity in an insect ( Caliothrips phaseoli ) revealed through a behavioural action spectrum. Proc. R. Soc. B 277 , 367–373 (2010).

IPCC Climate Change 2014: Impacts, Adaptation, and Vulnerability (eds Field, C. B. et al.) (Cambridge Univ. Press, 2014).

Steinbauer, M. J. et al. Accelerated increase in plant species richness on mountain summits is linked to warming. Nature 556 , 231–234 (2018).

Urmy, S. S. et al. Vertical redistribution of zooplankton in an oligotrophic lake associated with reduction in ultraviolet radiation by wildfire smoke. Geophys. Res. Lett. 43 , 3746–3753 (2016).

Ma, Z., Li, W., Shen, A. & Gao, K. Behavioral responses of zooplankton to solar radiation changes: in situ evidence. Hydrobiologia 711 , 155–163 (2013).

Leach, T. H., Williamson, C. E., Theodore, N., Fischer, J. M. & Olson, M. H. The role of ultraviolet radiation in the diel vertical migration of zooplankton: an experimental test of the transparency-regulator hypothesis. J. Plankton Res. 37 , 886–896 (2015).

Fischer, J. M. et al. Diel vertical migration of copepods in mountain lakes: the changing role of ultraviolet radiation across a transparency gradient. Limnol. Oceanogr. 60 , 252–262 (2015).

Cohen, J. M., Lajeunesse, M. J. & Rohr, J. R. A global synthesis of animal phenological responses to climate change. Nat. Clim. Change 8 , 224–228 (2018).

Predick, K. I. et al. UV-B radiation and shrub canopy effects on surface litter decomposition in a shrub-invaded dry grassland. J. Arid Environ. 157 , 13–21 (2018).

Kauko, H. M. et al. Windows in Arctic sea ice: light transmission and ice algae in a refrozen lead. J. Geophys. Res. Biogeosci. 122 , 1486–1505 (2017).

Williamson, C. E. et al. Climate change-induced increases in precipitation are reducing the potential for solar ultraviolet radiation to inactivate pathogens in surface waters. Sci. Rep. 7 , 13033 (2017).

Arnold, M. et al. Global burden of cutaneous melanoma attributable to ultraviolet radiation in 2012. Int. J. Cancer 143 , 1305–1314 (2018).

van Dijk, A. et al. Skin cancer risks avoided by the Montreal Protocol—worldwide modeling integrating coupled climate–chemistry models with a risk model for UV. Photochem. Photobiol. 89 , 234–246 (2013).

Flaxman, S. R. et al. Global causes of blindness and distance vision impairment 1990–2020: a systematic review and meta-analysis. Lancet Glob. Health 5 , e1221–e1234 (2017).

Sandhu, P. K. et al. Community-wide interventions to prevent skin cancer: two community guide systematic reviews. Am. J. Prev. Med. 51 , 531–539 (2016).

Gordon, L. G. & Rowell, D. Health system costs of skin cancer and cost-effectiveness of skin cancer prevention and screening: a systematic review. Eur. J. Cancer Prev. 24 , 141–149 (2015).

Hodzic, A. & Madronich, S. Response of surface ozone over the continental United States to UV radiation. Nat. Clim. Atmos. Sci. 1 , 35 (2018).

Ballaré, C. L., Caldwell, M. M., Flint, S. D., Robinson, S. A. & Bornman, J. F. Effects of solar ultraviolet radiation on terrestrial ecosystems. Patterns, mechanisms, and interactions with climate change. Photochem. Photobiol. Sci. 10 , 226–241 (2011).

Uchytilova, T. et al. Ultraviolet radiation modulates C:N stoichiometry and biomass allocation in Fagus sylvatica saplings cultivated under elevated CO 2 concentration. Plant Physiol. Biochem. 134 , 103–112 (2018).

Robson, T. M., Hartikainen, S. M. & Aphalo, P. J. How does solar ultraviolet-B radiation improve drought tolerance of silver birch ( Betula pendula Roth.) seedlings? Plant Cell Environ. 38 , 953–967 (2015).

Jenkins, G. I. Photomorphogenic responses to ultraviolet-B light. Plant Cell Environ. 40 , 2544–2557 (2017).

Šuklje, K. et al. Effect of leaf removal and ultraviolet radiation on the composition and sensory perception of Vitis vinifera L. cv. Sauvignon Blanc wine. Aust. J. Grape Wine Res. 20 , 223–233 (2014).

Escobar-Bravo, R., Klinkhamer, P. G. L. & Leiss, K. A. Interactive effects of UV-B light with abiotic factors on plant growth and chemistry, and their consequences for defense against arthropod herbivores. Front. Plant Sci. 8 , 278 (2017).

Ballaré, C. L., Mazza, C. A., Austin, A. T. & Pierik, R. Canopy light and plant health. Plant Physiol. 160 , 145–155 (2012).

Wargent, J. J. in The Role of UV-B Radiation in Plant Growth and Development (ed. Jordan, B. R.) 162–176 (CABI, 2017).

Zagarese, H. E. & Williamson, C. E. The implications of solar UV radiation exposure for fish and fisheries. Fish. Fish. 2 , 250–260 (2001).

Tucker, A. J. & Williamson, C. E. The invasion window for warmwater fish in clearwater lakes: the role of ultraviolet radiation and temperature. Divers. Distrib. 20 , 181–192 (2014).

Neale, P. J. & Thomas, B. C. Inhibition by ultraviolet and photosynthetically available radiation lowers model estimates of depth-integrated picophytoplankton photosynthesis: global predictions for Prochlorococcus and Synechococcus . Glob. Chang. Biol. 23 , 293–306 (2017).

Garcia-Corral, L. S. et al. Effects of UVB radiation on net community production in the upper global ocean. Glob. Ecol. Biogeogr. 26 , 54–64 (2017).

Cory, R. M., Ward, C. P., Crump, B. C. & Kling, G. W. Sunlight controls water column processing of carbon in arctic fresh waters. Science 345 , 925–928 (2014).

Austin, A. T., Méndez, M. S. & Ballaré, C. L. Photodegradation alleviates the lignin bottleneck for carbon turnover in terrestrial ecosystems. Proc. Natl Acad. Sci. USA 113 , 4392–4397 (2016).

Almagro, M., Maestre, F. T., Martínez-López, J., Valencia, E. & Rey, A. Climate change may reduce litter decomposition while enhancing the contribution of photodegradation in dry perennial Mediterranean grasslands. Soil Biol. Biochem. 90 , 214–223 (2015).

Lindholm, M., Wolf, R., Finstad, A. & Hessen, D. O. Water browning mediates predatory decimation of the Arctic fairy shrimp Branchinecta paludosa . Freshw. Biol. 61 , 340–347 (2016).

Cuyckens, G. A. E., Christie, D. A., Domic, A. I., Malizia, L. R. & Renison, D., Climate change. and the distribution and conservation of the world’s highest elevation woodlands in the South American Altiplano. Glob. Planet. Change 137 , 79–87 (2016).

Poste, A. E., Braaten, H. F. V., de Wit, H. A., Sørensen, K. & Larssen, T. Effects of photodemethylation on the methylmercury budget of boreal Norwegian lakes. Environ. Toxicol. Chem. 34 , 1213–1223 (2015).

Tsui, M. M. et al. Occurrence, distribution, and fate of organic UV filters in coral communities. Environ. Sci. Technol. 51 , 4182–4190 (2017).

Corinaldesi, C. et al. Sunscreen products impair the early developmental stages of the sea urchin Paracentrotus lividus . Sci. Rep. 7 , 7815 (2017).

Fong, H. C., Ho, J. C., Cheung, A. H., Lai, K. & William, K. Developmental toxicity of the common UV filter, benophenone-2, in zebrafish embryos. Chemosphere 164 , 413–420 (2016).

Willenbrink, T. J., Barker, V. & Diven, D. The effects of sunscreen on marine environments. Cutis 100 , 369 (2017).

Clark, J. R. et al. Marine microplastic debris: a targeted plan for understanding and quantifying interactions with marine life. Front. Ecol. Environ. 14 , 317–324 (2016).

UNEP Frontiers: 2016 Report. Emerging Issues of Environmental Concern (UNEP, 2016).

Frank, H., Christoph, E. H., Holm-Hansen, O. & Bullister, J. L. Trifluoroacetate in ocean waters. Environ. Sci. Technol. 36 , 12–15 (2002).

Solomon, K. R. et al. Sources, fates, toxicity, and risks of trifluoroacetic acid and its salts: relevance to substances regulated under the Montreal and Kyoto Protocols. J. Toxicol. Environ. Health B 19 , 289–304 (2016).

Fleming, E. L., Jackman, C. H., Stolarski, R. S. & Douglass, A. R. A model study of the impact of source gas changes on the stratosphere for 1850–2100. Atmos. Chem. Phys. 11 , 8515–8541 (2011).

Eyring, V. et al. Long-term ozone changes and associated climate impacts in CMIP5 simulations. J. Geophys. Res. Atm. 118 , 5029–5060 (2013).

Montzka, S. A. et al. An unexpected and persistent increase in global emissions of ozone-depleting CFC-11. Nature 557 , 413–417 (2018).

Crutzen, P. J. Albedo enhancement by stratospheric sulfur injections: a contribution to resolve a policy dilemma? Clim. Change 77 , 211–220 (2006).

Tilmes, S. et al. Impact of very short-lived halogens on stratospheric ozone abundance and UV radiation in a geo-engineered atmosphere. Atmos. Chem. Phys. 12 , 10945–10955 (2012).

Nowack, P. J., Abraham, N. L., Braesicke, P. & Pyle, J. A. Stratospheric ozone changes under solar geoengineering: implications for UV exposure and air quality. Atmos. Chem. Phys. 16 , 4191–4203 (2016).

Madronich, S., Tilmes, S., Kravitz, B., MacMartin, D. & Richter, J. Response of surface ultraviolet and visible radiation to stratospheric SO 2 injections. Atmosphere 9 , 432 (2018).

Kayler, Z. E. et al. Experiments to confront the environmental extremes of climate change. Front. Ecol. Environ. 13 , 219–225 (2015).

Pecl, G. T. et al. Biodiversity redistribution under climate change: impacts on ecosystems and human well-being. Science 355 , eaai9214 (2017).

Millenium Ecosystem Assessment. Ecosystems and Human Well-being: Our Human Planet; Summary for Decision-makers , Vol. 5 (Island, 2005).

NASA Institute for Space Studies. GISS Surface Temperature Analysis (GISTEMP) (GISTEMP, accessed 24 July 2018); https://data.giss.nasa.gov/gistemp/

Hansen, J., Ruedy, R., Sato, M. & Lo, K. Global surface temperature change. Rev. Geophys. 48 , RG4004 (2010).

https://earthobservatory.nasa.gov/images/817/largest-ever-ozone-hole-over-antarctica (accessed 14 May 2019).

https://ozonewatch.gsfc.nasa.gov/ (accessed 14 May 2019).

Download references

Acknowledgements

This work has been supported by the UNEP Ozone Secretariat, and we thank T. Birmpili and S. Mylona for their guidance and assistance. Additional support was provided by the US Global Change Research Program (P.W.B., C.E.W. and S.M.), the J. H. Mullahy Endowment for Environmental Biology (P.W.B.), the US National Science Foundation (grants DEB 1360066 and DEB 1754276 to C.E.W.), the Australian Research Council (DP180100113 to S.A.R.) and the University of Wollongong’s Global Challenges Program (S.A.R.). We appreciate the contributions from other UNEP EEAP members and co-authors of the EEAP Quadrennial Report, including: M. Ilyas, Y. Takizawa, F. L. Figueroa, H. H. Redhwi and A. Torikai. Special thanks to A. Netherwood for his assistance in drafting and improving figures. This paper has been reviewed in accordance with the US Environmental Protection Agency’s (US EPA) peer and administrative review policies and approved for publication. Mention of trade names or commercial products does not constitute an endorsement or recommendation for use by the US EPA.

Author information

These authors contributed equally: Paul W. Barnes, Craig E. Williamson, Robyn M. Lucas, Sharon A. Robinson, Sasha Madronich, Nigel D. Paul.

Authors and Affiliations

Department of Biological Sciences and Environment Program, Loyola University New Orleans, New Orleans, LA, USA

Paul W. Barnes

Department of Biology, Miami University, Oxford, OH, USA

Craig E. Williamson

National Centre for Epidemiology and Population Health, The Australian National University, Canberra, Australia

Robyn M. Lucas

Centre for Sustainable Ecosystem Solutions, School of Earth, Atmosphere and Life Sciences & Global Challenges Program, University of Wollongong, Wollongong, New South Wales, Australia

Sharon A. Robinson

National Center for Atmospheric Research, Boulder, CO, USA

Sasha Madronich

Lancaster Environment Centre, Lancaster University, Lancaster, UK

Nigel D. Paul & Paul J. Young

Food Futures Institute, Murdoch University, Perth, Western Australia, Australia

Janet F. Bornman

Laboratory of Atmospheric Physics, Aristotle University of Thessaloniki, Thessaloniki, Greece

Alkiviadis F. Bais

Swiss Federal Institute of Aquatic Science and Technology (Eawag), Dübendorf, Switzerland

Barbara Sulzberger

Centre for Atmospheric Chemistry, School of Earth, Atmosphere and Life Sciences, University of Wollongong, Wollongong, New South Wales, Australia

Stephen R. Wilson

Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC, USA

Anthony L. Andrady

National Institute of Water and Atmospheric Research, Central Otago, New Zealand

Richard L. McKenzie

Smithsonian Environmental Research Center, Edgewater, MD, USA

Patrick J. Neale

Faculty of Agronomy and IFEVA-CONICET, University of Buenos Aires, Buenos Aires, Argentina

Amy T. Austin & Carlos L. Ballaré

Biospherical Instruments Inc., San Diego, CA, USA

Germar H. Bernhard

School of Environmental Sciences, University of Guelph, Guelph, Ontario, Canada

Keith R. Solomon

QIMR Berghofer Medical Research Institute, Herston, Queensland, Australia

Rachel E. Neale

Biomedical Sciences, University of Edinburgh Medical School, Edinburgh, UK

Mary Norval

Centre for Dermatology Research, The University of Manchester and Salford Royal NHS Foundation Trust, Manchester, UK

Lesley E. Rhodes

Centre for Ecology and Evolution in Microbial Model Systems, Linnaeus University, Kalmar, Sweden

Samuel Hylander

Department of Biological Sciences, Rensselaer Polytechnic Institute, Troy, NY, USA

Kevin C. Rose

The Institute for Global Risk Research, Bethesda, MD, USA

Janice Longstreth

Ptersa Environmental Consultants, Faerie Glen, South Africa

Pieter J. Aucamp

Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI, USA

Rose M. Cory

Department of Forest, Rangeland, and Fire Sciences, University of Idaho, Moscow, ID, USA

Stephan D. Flint

Department of Dermatology, Leiden University Medical Centre, Leiden, The Netherlands

Frank R. de Gruijl

Friedrich-Alexander University, Erlangen-Nürnberg, Germany

Donat-P. Häder

Finnish Meteorological Institute R&D/Climate Research, Helsinki, Finland

Anu M. Heikkilä

School of Biological, Earth and Environmental Sciences, University College Cork, Cork, Ireland

Marcel A. K. Jansen

Institute of Wood Science and Technology, Bengaluru, India

Krishna K. Pandey

Organismal and Evolutionary Biology, Vikki Plant Science Centre, University of Helsinki, Helsinki, Finland

T. Matthew Robson

Cancer Council Victoria, Melbourne, Australia

Craig A. Sinclair

Department of Marine Sciences, University of Gothenburg, Göteborg, Sweden

Sten-Åke Wängberg

CIESIN, Columbia University, New Hartford, CT, USA

Robert C. Worrest

Centre for Ophthalmology and Visual Science, University of Western Australia, Perth, Western Australia, Australia

Seyhan Yazar

St. John’s Institute of Dermatology, King’s College London, London, UK

Antony R. Young

US Environmental Protection Agency, Athens, GA, USA

Richard G. Zepp

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Contributions

All authors helped in the development and review of this paper. The lead authors P.W.B., C.E.W., R.M.L., S.A.R., S.M. and N.D.P. played major roles in conceptualizing and writing the document. P.W.B. organized and coordinated the paper and integrated comments and revisions on all the drafts. C.E.W., R.M.L., J.F.B., A.F.B., B.S., S.R.W. and A.L.A. provided content with the assistance of S.M., S.A.R., G.H.B., R.L.M., P.J.A., A.M.H., P.J.Y. (stratospheric ozone effects on UV and ozone-driven climate change), R.E.N., F.R.deG., M.N., L.E.R., C.A.S., S.Y., A.R.Y. (human health), P.W.B., S.A.R., C.L.B., S.D.F., M.A.K.J., T.M.R. (agriculture and terrestrial ecosystems), P.J.N., S.H., K.C.R., R.M.C., D.-P.H., S-Å.W., R.C.W. (fisheries and aquatic ecosystems), A.T.A., R.G.Z. (biogeochemistry and contaminants), K.R.S., J.L. (air quality and toxicology) and K.K.P. (materials). R.L.M. conducted the UV simulation modelling.

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Barnes, P.W., Williamson, C.E., Lucas, R.M. et al. Ozone depletion, ultraviolet radiation, climate change and prospects for a sustainable future. Nat Sustain 2 , 569–579 (2019). https://doi.org/10.1038/s41893-019-0314-2

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DOI : https://doi.org/10.1038/s41893-019-0314-2

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Scientific Assessment of Ozone Depletion: 2018

Twenty questions and answers about the ozone layer, twenty questions and answers about the ozone layer: 2018 update, recommended citation, twenty questions and answers about the ozone layer citation:.

Ross J. Salawitch (Lead Author), David W. Fahey, Michaela I. Hegglin, Laura A. McBride, Walter R. Tribett, Sarah J. Doherty, Twenty Questions and Answers About the Ozone Layer: 2018 Update, Scientific Assessment of Ozone Depletion: 2018 , 84 pp., World Meteorological Organization, Geneva, Switzerland, 2019.

The Twenty Questions and Answers About the Ozone Layer: 2018 Update is a component of the Scientific Assessment of Ozone Depletion: 2018 report. The report is prepared quadrennially by the Scientific Assessment Panel (SAP) of the Montreal Protocol on Substances that Deplete the Ozone Layer . The 2018 edition of the 20 Questions document is the fourth update of the original edition that appeared in the 2002 Assessment Report. The motivation behind this scientific publication is to tell the story of ozone depletion, ozone-depleting substances and the success of the Montreal Protocol. The questions and answers format divides the narrative into topics that can be read and studied individually by the intended audience of specialists and non-specialists. The topics range from the most basic (e.g., What is ozone?) to more recent developments (e.g., the Kigali Amendment). Each question begins with a short answer followed by a longer, more comprehensive answer. Figures enhance the narrative by illustrating key concepts and results. This document is principally based on scientific results presented in the 2018 and earlier Assessment Reports and has been extensively reviewed by scientists and non-specialists to ensure quality and readability.

We hope that you find this 20 Questions and Answers edition of value in communicating the scientific basis of ozone depletion and the success of the Montreal Protocol in protecting the ozone layer and future climate.

David W. Fahey, Paul A. Newman, John A. Pyle, and Bonfils Safari Co-Chairs of the Scientific Assessment Panel

Lead Author

See Appendix for Acknowledgements for the full list of contributors.

Introduction

Ozone is present only in small amounts in the atmosphere. Nevertheless, it is vital to human well-being as well as agricultural and ecosystem sustainability. Most of Earth's ozone resides in the stratosphere, the layer of the atmosphere that is more than 10 kilometers (6 miles) above the surface. About 90% of atmospheric ozone is contained in the stratospheric "ozone layer", which shields Earth's surface from harmful ultraviolet radiation emitted by the Sun.

In the mid-1970s scientists discovered that some human-produced chemicals could lead to depletion of the stratospheric ozone layer. The resulting increase in ultraviolet radiation at Earth's surface would increase the incidents of skin cancer and eye cataracts, and also adversely affect plants, crops, and ocean plankton.

Following the discovery of this environmental issue, researchers sought a better understanding of this threat to the ozone layer. Monitoring stations showed that the abundances of ozone-depleting substances (ODSs) were steadily increasing in the atmosphere. These trends were linked to growing production and use of chemicals like chlorofluorocarbons (CFCs) for spray can propellants, refrigeration and air conditioning, foam blowing, and industrial cleaning. Measurements in the laboratory and in the atmosphere characterized the chemical reactions that were involved in ozone destruction. Computer models of the atmosphere employing this information were used to simulate how much ozone depletion was already occurring and to predict how much more might occur in the future.

Observations of the ozone layer showed that depletion was indeed occurring. The most severe and most surprising ozone loss was discovered to be recurring in springtime over Antarctica. The loss in this region is commonly called the "ozone hole" because the ozone depletion is so large and localized. A thinning of the ozone layer also has been observed over other regions of the globe, such as the Arctic and northern and southern midlatitudes.

The work of many scientists throughout the world has built a broad and solid scientific understanding of the ozone depletion process. With this understanding, we know that ozone depletion is occurring and why. Most importantly, we know that if the most potent ODSs were to continue to be emitted and increase in the atmosphere, the result would be more depletion of the ozone layer.

In 1985 the world's governments adopted the Vienna Convention for the Protection of the Ozone Layer, in response to the prospect of increasing ozone depletion. The Vienna Convention provided a framework to protect the ozone layer. In 1987, this framework led to the Montreal Protocol on Substances that Deplete the Ozone Layer (the Montreal Protocol), an international treaty designed to control the production and consumption of CFCs and other ODSs. As a result of the broad compliance with the Montreal Protocol and its Amendments and Adjustments as well as industry's development of "ozone-friendly" substitutes to replace CFCs, the total global accumulation of ODSs in the atmosphere has slowed and begun to decrease. The replacement of CFCs has occurred in two phases: first via the use of hydrofluorocarbons (HCFCs) that cause considerably less damage to the ozone layer compared to CFCs, and second by the introduction of hydrofluorocarbons (HFCs) that pose no harm to ozone. In response, global ozone depletion has stabilized, and initial signs of recovery of the ozone layer have been identified. With continued compliance, substantial recovery of the ozone layer is expected by the middle of the 21st century. The day the Montreal Protocol was agreed upon, 16 September, is now celebrated as the International Day for the Preservation of the Ozone Layer.

The Amendment and Adjustment process is a vitally important aspect of the Montreal Protocol. At the Meeting of the Parties of the Montreal Protocol held in Kigali, Rwanda during October 2016, the Amendment process achieved an important new milestone, the Kigali Amendment. The Amendment phases down future global production and consumption of certain HFCs. While HFCs pose no threat to the ozone layer because they lack chlorine and bromine, they are greenhouse gases (GHGs), which lead to warming of surface climate. The amendment process was motivated by projections of substantial increases in the global use of HFCs in the coming decades. The control of HFCs under the Kigali Amendment marks the first time the Montreal Protocol has adopted regulations solely for the protection of climate.

The protection of the ozone layer and climate under the Montreal Protocol is a story of notable achievements: discovery, understanding, decisions, actions, and verification. It is a success story written by many: scientists, technologists, economists, legal experts, and policymakers, in which continuous dialogue has been a key ingredient. A timeline of milestones related to the science of stratospheric ozone depletion, international scientific assessments, and the Montreal Protocol is illustrated in Figure Q0-1 .

To help communicate the broad understanding of the Montreal Protocol, ODSs, and ozone depletion, as well as the relationship of these topics to GHGs and climate change, this component of the Scientfic Assessment of Ozone Depletion: 2018 describes the state of this science with 20 illustrated questions and answers. Most of the material is an update to that presented in previous Ozone Assessments . A new question has been added describing the expansion of climate protection under the Montreal Protocol ( Q19 ).

The questions address the nature of atmospheric ozone, the chemicals that cause ozone depletion, how global and polar ozone depletion occur, the extent of ozone depletion, the success of the Montreal Protocol, the possible future of the ozone layer, and the protection against climate change that is now provided by the Kigali Amendment. Computer model projections show that GHGs and changes in climate will have a growing in uence on global ozone in the coming decades, and in some cases will exceed the in uence of ODSs in most atmospheric regions by the end of this century. Ozone and climate are indirectly linked because both ODSs and their substitutes as well as ozone itself are GHGs that contribute to climate change.

A brief answer to each question is first given in dark red; an expanded answer then follows. The answers are based on the information presented in the 2018 and earlier Assessment reports as well as other international scientfic assessments. These reports and the answers provided here were prepared and reviewed by a large number of international scientists who are experts in different research fields related to the science of stratospheric ozone and climate 1 .

1 See Appendix for Acknowledgments .

Ozone in our atmosphere

Q1 what is ozone, how is it formed, and where is it in the atmosphere.

Ozone is a gas that is naturally present in our atmosphere. Each ozone molecule contains three atoms of oxygen and is denoted chemically as O 3 . Ozone is found primarily in two regions of the atmosphere. About 10% of Earth’s ozone is in the troposphere, which extends from the surface to about 10–15 kilometers (6–9 miles) altitude. About 90% of Earth’s ozone resides in the stratosphere, the region of the atmosphere between the top of the troposphere and about 50 kilometers (31 miles) altitude. The part of the stratosphere with the highest amount of ozone is commonly referred to as the “ozone layer”. Throughout the atmosphere, ozone is formed in multistep chemical processes that are initiated by sunlight. In the stratosphere, the process begins with an oxygen molecule (O 2 ) being broken apart by ultraviolet radiation from the Sun. In the troposphere, ozone is formed by a different set of chemical reactions that involve naturally occurring gases as well as those from sources of air pollution.

Ozone is a gas that is naturally present in our atmosphere. Ozone has the chemical formula O 3 because an ozone molecule contains three oxygen atoms (see Figure Q1-1 ). Ozone was discovered in laboratory experiments in the mid-1800s. Ozone’s presence in the atmosphere was later discovered using chemical and optical measurement methods. The word ozone is derived from the Greek word óζειν (ozein) , meaning “to smell.” Ozone has a pungent odor that allows it to be detected even at very low amounts. Ozone reacts rapidly with many chemical compounds and is explosive in concentrated amounts. Electrical discharges are generally used to produce ozone for industrial processes such as air and water purification and bleaching of textiles and food products.

Ozone location. Most ozone (about 90%) is found in the stratosphere, which begins about 10–15 kilometers (km) above Earth’s surface and extends up to about 50 km altitude. The stratospheric region with the highest concentration of ozone, between about 15 and 35 km altitude, is commonly known as the “ozone layer” (see Figure Q1-2 ). The ozone layer extends over the entire globe with some variation in altitude and thickness. Most of the remaining ozone (about 10%) is found in the troposphere, which is the lowest region of the atmosphere, between Earth’s surface and the stratosphere. Tropospheric air is the “air we breathe” and, as such, excess ozone in the troposphere has harmful consequences (see Q2 ).

Ozone abundance. Ozone molecules have a low relative abundance in the atmosphere. Most air molecules are either oxygen (O 2 ) or nitrogen (N 2 ). In the stratosphere near the peak concentration of the ozone layer, there are typically a few thousand ozone molecules for every billion air molecules (1 billion = 1,000 million). In the troposphere near Earth’s surface, ozone is even less abundant, with a typical range of 20 to 100 ozone molecules for each billion air molecules. The highest ozone values near the surface occur in air that is polluted by human activities.

As an illustration of the low relative abundance of ozone in our atmosphere, one can imagine bringing all the ozone molecules in the troposphere and stratosphere down to Earth’s surface and forming a layer of pure ozone that extends over the entire globe. The resulting layer would have an average thickness of about three millimeters (0.12 inches) (see Q3 ). Nonetheless, this extremely small fraction of the atmosphere plays a vital role in protecting life on Earth (see Q2 ).

Stratospheric ozone. Stratospheric ozone is formed naturally by chemical reactions involving solar ultraviolet radiation (sunlight) and oxygen molecules, which make up about 21% of the atmosphere. In the first step, solar ultraviolet radiation breaks apart one oxygen molecule (O 2 ) to produce two oxygen atoms (2 O) (see Figure Q1-3 ). In the second step, each of these highly reactive oxygen atoms combines with an oxygen molecule to produce an ozone molecule (O 3 ). 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.

The production of stratospheric ozone is balanced by its destruction in chemical reactions. Ozone reacts continually with sunlight and a wide variety of natural and human-produced chemicals in the stratosphere. In each reaction, an ozone molecule is lost and other chemical compounds are produced. Important reactive gases that destroy ozone are hydrogen and nitrogen oxides and those containing chlorine and bromine (see Q7 ). Some stratospheric ozone is regularly transported down into the troposphere and can occasionally influence ozone amounts at Earth’s surface.

Tropospheric ozone. Near Earth’s surface, ozone is produced by chemical reactions involving gases emitted to the atmosphere from both natural sources and human activities. Ozone production reactions primarily involve hydrocarbon and nitrogen oxide gases, as well as ozone itself, and all require sunlight for completion. Fossil fuel combustion is a primary source of pollutant gases that lead to tropospheric ozone production. As in the stratosphere, ozone in the troposphere is destroyed by naturally occurring chemical reactions and by reactions involving human-produced chemicals. Tropospheric ozone can also be destroyed when ozone reacts with a variety of surfaces, such as those of soils and plants.

Balance of chemical processes. Ozone abundances in the stratosphere and troposphere are determined by the balance between chemical processes that produce and destroy ozone. The balance is determined by the amounts of reactive gases and how the rate or effectiveness of the various reactions varies with sunlight intensity, location in the atmosphere, temperature, and other factors. As atmospheric conditions change to favor ozone-producing reactions in a certain location, ozone abundances increase. Similarly, if conditions change to favor other reactions that destroy ozone, abundances decrease. The balance of production and loss reactions, combined with atmospheric air motions that transport and mix air with different ozone abundances, determines the global distribution of ozone on timescales of days to many months (see also Q3 ). Global stratospheric ozone has decreased during the past several decades (see Q12 ) because the amounts of reactive gases containing chlorine and bromine have increased in the stratosphere due to human activities (see Q6 and Q15 ).

Q2 Why do we care about atmospheric ozone?

Ozone in the stratosphere absorbs a large part of the Sun’s biologically harmful ultraviolet radiation. Stratospheric ozone is considered “good” ozone because of this beneficial role. In contrast, ozone formed at Earth’s surface in excess of natural amounts is considered “bad” ozone because it is harmful to humans, plants, and animals.

Ozone in the stratosphere (Good ozone). Stratospheric ozone is considered good for humans and other life forms because it absorbs ultraviolet (UV) radiation from the Sun (see Figure Q2-1 ). If not absorbed, high energy UV radiation would reach Earth’s surface in amounts that are harmful to a variety of life forms. The Sun emits three types of UV radiation: UV-C (100 to 280 nanometer (nm) wavelengths); UV-B (280 to 315 nm), and UV-A (315 to 400 nm). Exposure to UV-C radiation is particularly dangerous to all life forms. Fortunately, UV-C radiation is entirely absorbed within the ozone layer. Most UV-B radiation emitted by the Sun is absorbed by the ozone layer; the rest reaches Earth’s surface. In humans, increased exposure to UV-B radiation raises the risks of skin cancer and cataracts, and suppresses the immune system. Exposure to UV-B radiation before adulthood and cumulative exposure are both important health risk factors. Excessive UV-B exposure also can damage terrestrial plant life, including agricultural crops, single-celled organisms, and aquatic ecosystems. Low energy UV radiation, UV-A, which is not absorbed significantly by the ozone layer, causes premature aging of the skin.

Protecting stratospheric ozone. In the mid-1970s, it was discovered that gases containing chlorine and bromine atoms released by human activities could cause stratospheric ozone depletion (see Q5 and Q6 ). These gases, referred to as halogen source gases, and also as ozone-depleting substances (ODSs), chemically release their chlorine and bromine atoms after they reach the stratosphere. Ozone depletion increases surface UV-B radiation above naturally occurring amounts. International efforts have been successful in protecting the ozone layer through controls on the production and consumption of ODSs (see Q14 and Q15 ).

Ozone in the troposphere (Bad ozone). Ozone near Earth’s surface in excess of natural amounts is considered bad ozone (see Figure Q1-2 ). Surface ozone in excess of natural levels is formed by reactions involving air pollutants emitted from human activities, such as nitrogen oxides (NOx), carbon monoxide (CO), and various hydrocarbons (gases containing hydrogen, carbon, and often oxygen). Exposure to surface ozone above natural levels is harmful to humans, plants, and other living systems because ozone reacts strongly to destroy or alter many biological molecules. Enhanced surface ozone caused by air pollution reduces crop yields and forest growth. In humans, exposure to high levels of ozone can reduce lung capacity; cause chest pains, throat irritation, and coughing; and worsen pre-existing health conditions related to the heart and lungs. In addition, increases in tropospheric ozone lead to a warming of Earth’s surface because ozone is a greenhouse gas (GHG) (see Q17 ). The negative effects of excess tropospheric ozone contrast sharply with the protection from harmful UV radiation afforded by preserving the natural abundance of stratospheric ozone.

Reducing tropospheric ozone. Limiting the emission of certain common pollutants reduces the production of excess ozone near Earth’s surface where it can affect humans, plants, and animals. Major sources of pollutants include large cities where fossil fuel consumption and industrial activities are greatest. Many programs around the globe have been successful in reducing or limiting the emission of pollutants that cause production of excess ozone near Earth’s surface.

Natural ozone. In the absence of human activities, ozone would still be present near Earth’s surface and throughout the troposphere and stratosphere because ozone is a natural component of the clean atmosphere. Natural emissions from the biosphere, mainly from trees, participate in chemical reactions that produce ozone. Atmospheric ozone plays important ecological roles beyond absorbing UV radiation. For example, ozone initiates the chemical removal of many pollutants as well as some GHGs, such as methane (CH 4 ). In addition, the absorption of UV radiation by ozone is a natural source of heat in the stratosphere, causing temperatures to increase with altitude. Stratospheric temperatures affect the balance of ozone production and destruction processes (see Q1 ) and air motions that redistribute ozone throughout the stratosphere (see Q3 ).

Q3 How is total ozone distributed over the globe?

The distribution of total ozone over Earth varies with geographic location and on daily to seasonal timescales. These variations are caused by large-scale movements of stratospheric air and the chemical production and destruction of ozone. Total ozone is generally lowest at the equator and highest in midlatitude and polar regions.

Total ozone. The total ozone column at any location on the globe is defined as the sum of all the ozone in the atmosphere directly above that location. Most ozone resides in the stratospheric ozone layer and a small percentage (about 10%) is distributed throughout the troposphere (see Q1 ). Total ozone column values are often reported in Dobson units denoted as “DU.” Typical values vary between 200 and 500 DU over the globe, with a global average abundance of about 300 DU (see Figure Q3-1 ). The quantity of ozone molecules required for total ozone to be 300 DU could form a layer of pure ozone gas at Earth’s surface having a thickness of only 3 millimeters (0.12 inches) (see Q1 ), which is about the height of a stack of 2 common coins. It is remarkable that a layer of pure ozone only 3 millimeters thick protects life on Earth’s surface from harmful UV radiation emitted by the Sun (see Q2 ).

Global distribution. Total ozone varies strongly with latitude over the globe, with the largest values occurring at middle and high latitudes during most of the year (see Figure Q3-1 ). This distribution is the result of the large-scale circulation of air in the stratosphere that slowly transports ozone from the tropics, where ozone production from solar ultraviolet radiation is highest, toward the poles. Ozone accumulates at middle and high latitudes, increasing the vertical extent of the ozone layer and, at the same time, total ozone. Values of total ozone are generally smallest in the tropics for all seasons. An exception in recent decades is the region of low values of ozone over Antarctica during spring in the Southern Hemisphere, a phenomenon known as the Antarctic ozone hole (dark blue, Figure Q3-1 ; also see Q10 and Q11 ).

Seasonal distribution. Total ozone also varies with season, as shown in Figure Q3-1 using two-week averages of ozone taken from 2009 satellite observations. March and September plots represent the early spring and autumn seasons in the Northern and Southern Hemispheres. June and December plots similarly represent the early summer and winter seasons. During spring, total ozone exhibits maximums at latitudes poleward of about 45° N in the Northern Hemisphere and between 45° and 60° S in the Southern Hemisphere. These spring maximums are a result of increased transport of ozone from its source region in the tropics toward high latitudes during late autumn and winter. This poleward ozone transport is much weaker during the summer and early autumn periods and is weaker overall in the Southern Hemisphere.

This natural seasonal cycle can be observed clearly in the Northern Hemisphere as shown in Figure Q3-1 , with increasing values in Arctic total ozone during winter, a clear maximum in spring, and decreasing values from summer to autumn. In the Antarctic, however, a pronounced minimum in total ozone is observed during spring. The minimum is known as the “ozone hole”, which is caused by the widespread chemical depletion of ozone in spring by pollutants known as ozone-depleting substances (see Q5 and Q10 ). In the late 1970s, before the ozone hole appeared each year, much higher ozone values than those currently observed were found in the Antarctic spring (see Q10 ). Now, the lowest values of total ozone across the globe and all seasons are found every late winter/early spring in the Antarctic as shown in Figure Q3-1 . After spring, these low values disappear from total ozone maps as polar air mixes with lower-latitude air containing much higher amounts of ozone.

In the tropics, the change in total ozone through the progression of the seasons is much smaller than in the polar regions. This feature is due to seasonal changes in both sunlight and ozone transport being much smaller in the tropics compared to polar regions.

Natural variations. Total ozone varies strongly with latitude and longitude as seen within the seasonal plots in Figure Q3-1 . These patterns come about for two reasons. First, atmospheric winds transport air between regions of the stratosphere that have high ozone values and those that have low ozone values. Tropospheric weather systems can temporarily alter the vertical extent of the ozone layer in a region, and thereby change total ozone. The regular nature of these air motions, in some cases associated with geographical features (oceans and mountains), in turn causes recurring patterns in the distribution of total ozone.

Second, ozone variations occur as a result of changes in the balance of chemical production and loss processes as air moves to and from different locations over the globe. This balance, for example, is very sensitive to the amount of sunlight in a region.

There is a good understanding of how chemistry and air motions work together to cause the observed large-scale features in total ozone, such as those seen in Figure Q3-1 . Ozone changes are routinely monitored by a large group of investigators using satellite, airborne, and ground-based instruments. The continued analyses of these observations provide an important basis to quantify the contribution of human activities to ozone depletion.

Q4 How is ozone measured in the atmosphere?

The amount of ozone in the atmosphere is measured by instruments on the ground and carried aloft on balloons, aircraft, and satellites. Some instruments measure ozone locally by continuously drawing air samples into a small detection chamber. Other instruments measure ozone remotely over long distances by using ozone’s unique optical absorption or emission properties.

The abundance of ozone in the atmosphere is measured by a variety of techniques (see Figure Q4-1 ). The techniques make use of ozone’s unique optical and chemical properties. There are two principal categories of measurement techniques: local and remote. Ozone measurements by these techniques have been essential in monitoring changes in the ozone layer and in developing our understanding of the processes that control ozone abundances.

Local measurements. Local measurements of the atmospheric abundance of ozone are those that require air to be drawn directly into an instrument. Once inside an instrument’s detection chamber, the amount of ozone is determined by measuring the absorption of ultraviolet (UV) light or by the electrical current or light produced in a chemical reaction involving ozone. The last approach is used in “ozonesondes” that are lightweight, ozone-measuring modules suitable for launching on small balloons. The balloons ascend up to altitudes of about 32 to 35 kilometers (km), high enough to measure ozone in the stratospheric ozone layer. Ozonesondes are launched regularly at many locations around the world. Local ozone-measuring instruments using optical or chemical detection schemes are also used on research aircraft to measure the distribution of ozone in the troposphere and lower stratosphere (up to altitudes of about 20 km). High-altitude research aircraft can reach the ozone layer at most locations over the globe and can reach furthest into the layer at high latitudes. Ozone measurements are also being made routinely on some commercial aircraft flights.

Remote measurements. Remote measurements of total ozone amounts and the altitude distributions of ozone are obtained by detecting ozone at large distances from the instrument. Most remote measurements of ozone rely on its unique absorption of UV radiation. Sources of UV radiation that can be used are the Sun, lasers, and starlight. For example, satellite instruments use the absorption of solar UV radiation by the atmosphere or the absorption of sunlight scattered from the surface of Earth to measure ozone over nearly the entire globe on a daily basis. Lidar instruments, which measure backscattered laser light, are routinely deployed at ground sites and on research aircraft to detect ozone over a distance of many kilometers along the laser light path. A network of ground-based detectors measures ozone by detecting small changes in the amount of the Sun’s UV radiation that reaches Earth’s surface. Other instruments measure ozone using its absorption of infrared or visible radiation or its emission of microwave or infrared radiation at different altitudes in the atmosphere, thereby obtaining information on the vertical distribution of ozone. Emission measurements have the advantage of providing remote ozone measurements at night, which is particularly valuable for sampling polar regions during winter, when there is continuous darkness.

The ozone depletion process

Q5 how do emissions of halogen source gases lead to stratospheric ozone depletion.

The initial step in the depletion of stratospheric ozone by human activities is the emission, at Earth’s surface, of gases that contain chlorine and bromine and have long atmospheric lifetimes. Most of these gases accumulate in the lower atmosphere because they are relatively unreactive and do not dissolve readily in rain or snow. Natural air motions transport these accumulated gases to the stratosphere, where they are converted to more reactive gases. Some of these gases then participate in reactions that destroy ozone. Finally, when air returns to the lower atmosphere, these reactive chlorine and bromine gases are removed from Earth’s atmosphere by rain and snow.

Emission, accumulation, and transport. The principal steps in stratospheric ozone depletion caused by human activities are shown in Figure Q5-1 . The process begins with the emission, at Earth’s surface, of long-lived source gases containing the halogens chlorine and bromine (see Q6 ). The halogen source gases, often referred to as ozone-depleting substances (ODSs), include manufactured chemicals released to the atmosphere in a variety of applications, such as refrigeration, air conditioning, and foam blowing. Chlorofluorocarbons (CFCs) are an important example of a chlorine-containing source gas. Emitted source gases accumulate in the lower atmosphere (troposphere) and are transported to the stratosphere by natural air motions. The accumulation occurs because most source gases are highly unreactive in the lower atmosphere. Small amounts of these gases dissolve in ocean waters. The low reactivity of these manufactured halogenated gases is one property that made them well suited for specialized applications such as refrigeration.

Some halogen gases are emitted in substantial quantities from natural sources (see Q6 ). These emissions also accumulate in the troposphere, are transported to the stratosphere, and participate in ozone destruction reactions. These naturally emitted gases are part of the natural balance of ozone production and destruction that predates the large release of manufactured halogenated gases.

Conversion, reaction, and removal. Halogen source gases do not react directly with ozone. Once in the stratosphere, halogen source gases are chemically converted to reactive halogen gases by ultraviolet radiation from the Sun (see Q7 ). The rate of conversion is related to the atmospheric lifetime of a gas (see Q6 ). Gases with longer lifetimes have slower conversion rates and survive longer in the atmosphere after emission. Lifetimes of the principal ODSs vary from about 1 to 100 years (see Table Q6-1 ). Emitted gas molecules with atmospheric lifetimes greater than a few years circulate between the troposphere and stratosphere multiple times, on average, before conversion occurs.

The reactive gases formed from halogen source gases react chemically to destroy ozone in the stratosphere (see Q8 ). The average depletion of total ozone attributed to reactive gases is smallest in the tropics and largest at high latitudes (see Q12 ). In polar regions, surface reactions that occur at low temperatures on polar stratospheric clouds greatly increase the abundance of the most reactive chlorine gas, chlorine monoxide (ClO) (see Q9 ). This process results in substantial ozone destruction in polar regions in late winter/early spring (see Q10 and Q11 ).

After a few years, air in the stratosphere returns to the troposphere, bringing along reactive halogen gases. These reactive halogen gases are then removed from the atmosphere by rain and other precipitation or deposited on Earth’s land or ocean surfaces. This removal brings to an end the destruction of ozone by chlorine and bromine atoms that were first released to the atmosphere as components of halogen source gas molecules.

Tropospheric conversion. Halogen source gases with short lifetimes (less than 1 year) undergo significant chemical conversion in the troposphere, producing reactive halogen gases and other compounds. Source gas molecules that are not converted are transported to the stratosphere. Only small portions of reactive halogen gases produced in the troposphere are transported to the stratosphere because most are removed by precipitation. Important examples of halogen gases that undergo some tropospheric removal are the hydrochlorofluorocarbons (HCFCs), methyl bromide (CH 3 Br), methyl chloride (CH 3 Cl), and gases containing iodine (see Q6 ).

Q6 What emissions from human activities lead to ozone depletion?

Certain industrial processes and consumer products result in the emission of ozone-depleting substances (ODSs) to the atmosphere. ODSs are manufactured halogen source gases that are controlled worldwide by the Montreal Protocol. These gases bring chlorine and bromine atoms to the stratosphere, where they destroy ozone in chemical reactions. Important examples are the chlorofluorocarbons (CFCs), once used in almost all refrigeration and air conditioning systems, and the halons, which were used as fire extinguishing agents. Current ODS abundances in the atmosphere are known directly from air sample measurements.

Halogen source gases versus ozone-depleting substances (ODSs). Those halogen source gases emitted by human activities and controlled by the Montreal Protocol are referred to as ODSs within the Montreal Protocol, by the media, and in the scientific literature. The Montreal Protocol controls the global production and consumption of ODSs (see Q14 ). Halogen source gases such as methyl chloride (CH 3 Cl) that have predominantly natural sources are not classified as ODSs. The contributions of ODSs and natural halogen source gases to the total amount of chlorine and bromine entering the stratosphere, which peaked in 1993 and 1998, respectively, are shown in Figure Q6-1 . The difference in the timing of the peaks is a result of different phaseout schedules specified by the Montreal Protocol, atmospheric lifetimes, and the time delays between production and emissions of the various source gases. Also shown are the contributions to total chlorine and bromine in 2016, highlighting the reductions of 10% and 11%, respectively, achieved under the controls of the Montreal Protocol.

Ozone-depleting substances (ODSs). ODSs are manufactured for specific industrial uses or consumer products, most of which result in the eventual emission of these gases to the atmosphere. Total ODS emissions increased substantially from the middle to the late 20th century, reached a peak in the late 1980s, and are now in decline (see Figure Q0-1 ). A large fraction of the emitted ODSs reach the stratosphere, where they are converted to reactive gases containing chlorine and bromine that lead to ozone depletion.

ODSs containing only carbon, chlorine, and fluorine are called chlorofluorocarbons, usually abbreviated as CFCs. The principal CFCs are CFC-11 (CCl 3 F), CFC-12 (CCl 2 F 2 ), and CFC-113 (CCl 2 FCClF 2 ). CFCs, along with carbon tetrachloride (CCl 4 ) and methyl chloroform (CH 3 CCl 3 ), historically have been the most important chlorine-containing halogen source gases emitted by human activities. These and other chlorine-containing ODSs have been used in many applications, including refrigeration, air conditioning, foam blowing, spray can propellants, and cleaning of metals and electronic components. As a result of the Montreal Protocol controls, the abundances of most of these chlorine source gases have decreased since 1993 (see Figure Q6-1 ). The concentrations of CFC-11 and CFC-12 peaked in 1994 and 2002, respectively, and have since decreased (see Figure Q15-1 ). The abundance of CFC-11 in 2016 was 14% lower than its peak value, while that of CFC-12 in 2016 was 5% lower than its peak (see Figure Q15-1 ). As substitute gases for CFCs, the atmospheric abundances of hydrochlorofluorocarbons (HCFCs) increased substantially between 1993 and 2016 (+175%). With restrictions on global production in place since 2013, the atmospheric abundances of HCFCs are expected to peak between 2020 and 2030.

Another category of ODSs contains bromine. The most important of these gases are the halons and methyl bromide (CH 3 Br). Halons are a group of industrial compounds that contain at least one bromine and one carbon atom; halons may or may not contain a chlorine atom. Halons were originally developed to extinguish fires and were widely used to protect large computer installations, military hardware, and commercial aircraft engines. As a consequence, upon use halons are released directly into the atmosphere. Halon-1211 and halon-1301 are the most abundant halons emitted by human activities.

Methyl bromide is used primarily as a fumigant for pest control in agriculture and disinfection of export shipping goods, and also has significant natural sources. As a result of the Montreal Protocol, the contribution to the atmospheric abundance of methyl bromide from human activities has substantially decreased between 1998 and 2016 (−68%; see Figure Q6-1 ). Halon-1211 reached peak concentration in 2005 and has been decreasing ever since, reaching an abundance in 2016 that was 8.2% below that measured in 1998. The abundance of halon-1301, on the other hand, has increased by 23% since 1998 and is expected to continue to increase very slightly into the next decade because of continued small releases and a long atmospheric lifetime (see Figure Q15-1 ). The bromine content of other halons (mainly halon-1202 and halon-2402) in 2016 was 21% below the amount present in 1998.

Natural sources of chlorine and bromine. There are a few halogen source gases present in the stratosphere that have large natural sources. These include methyl chloride (CH 3 Cl) and methyl bromide (CH 3 Br), both of which are emitted by oceanic and terrestrial ecosystems. In addition, very short-lived source gases containing bromine such as bromoform (CHBr 3 ) and dibromomethane (CH 2 Br 2 ) are also released to the atmosphere, primarily from biological activity in the oceans. Only a fraction of the emissions of very short-lived source gases reaches the stratosphere because these gases are efficiently removed in the lower atmosphere. Volcanoes provide an episodic source of reactive halogen gases that sometimes reach the stratosphere in appreciable quantities. Other natural sources of halogens include reactive chlorine and bromine produced by evaporation of ocean spray. These reactive chemicals readily dissolve in water and are removed in the troposphere. In 2016, natural sources contributed about 16% of total stratospheric chlorine and about 50% of total stratospheric bromine (see Figure Q6-1 ). The amount of chlorine and bromine entering the stratosphere from natural sources is fairly constant over time and, therefore, cannot be the cause of the ozone depletion observed since the 1980s.

Other human activities that are sources of chlorine and bromine gases. Other chlorine- and bromine-containing gases are released to the atmosphere from human activities. Common examples are the use of chlorine-containing solvents and industrial chemicals, and the use of chlorine gases in paper production and disinfection of potable and industrial water supplies (including swimming pools). Most of these gases are very short-lived and only a small fraction of their emissions reaches the stratosphere. The contribution of very short-lived chlorinated gases from natural sources and human activities to total stratospheric chlorine was 44% larger in 2016 compared to 1993, and now contributes about 3.5% (115 ppt) of the total chlorine entering the stratosphere (see Figure Q6-1 ). The Montreal Protocol does not control the production and consumption of very short-lived chlorine source gases, although the atmospheric abundances of some (notably dichloromethane, CH 2 Cl 2 ) have increased substantially in recent years. Solid rocket engines, such as those used to propel payloads into orbit, release reactive chlorine gases directly into the troposphere and stratosphere. The quantities of chlorine emitted globally by rockets is currently small in comparison with halogen emissions from other human activities.

Lifetimes and emissions. Estimates of global emissions in 2016 for a selected set of halogen source gases are given in Table Q6-1 . These emissions occur from continued production of HCFCs and hydrofluorocarbons (HFCs) as well as the release of gases from banks. Emission from banks refers to the atmospheric release of halocarbons from existing equipment, chemical stockpiles, foams, and other products. In 2016 the global emission of the refrigerant HCFC-22 (CHF 2 Cl) constituted the largest annual release, by mass, of a halocarbon from human activities. Release in 2016 of HFC-134a (CH 2 FCF 3 ), another refrigerant, was second largest. The emission of methyl chloride (CH 3 Cl) is primarily from natural sources such as the ocean biosphere, terrestrial plants, salt marshes and fungi. The human source of methyl chloride is small relative to the total natural source (see Q15 ).

After emission, halogen source gases are either naturally removed from the atmosphere or undergo chemical conversion in the troposphere or stratosphere. The time to remove or convert about 63% of a gas is often called its atmospheric lifetime. Lifetimes vary from less than 1 year to 100 years for the principal chlorine- and bromine-containing gases (see Table Q6-1 ). The long-lived gases are converted to other gases primarily in the stratosphere and essentially all of their original halogen content becomes available to participate in the destruction of stratospheric ozone. Gases with short lifetimes such as HCFCs, methyl bromide, and methyl chloride are effectively converted to other gases in the troposphere, which are then removed by rain and snow. Therefore, only a fraction of their halogen content potentially contributes to ozone depletion in the stratosphere. Methyl chloride, despite its large source, constituted only about 17% (555 ppt) of the halogen source gases entering the stratosphere in 2016 (see Figure Q6-1 ).

The amount of an emitted gas that is present in the atmosphere represents a balance between its emission and removal rates. A wide range of current emission rates and atmospheric lifetimes are derived for the various source gases (see Table Q6-1 ). The atmospheric abundances of most of the principal CFCs and halons have decreased since 1990 in response to smaller emission rates, while those of the leading substitute gases, the HCFCs, continue to increase under the provisions of the Montreal Protocol (see Q15 ). In the past few years, the rate of the increase of the atmospheric abundance of HCFCs has slowed down. In the coming decades, the emissions and atmospheric abundances of all controlled gases are expected to decrease under these provisions.

Ozone Depletion Potential (ODP). Emissions of halogen source gases are compared in their effectiveness to destroy stratospheric ozone based upon their ODPs, as listed in Table Q6-1 (see Q17 ). Once in the atmosphere, a gas with a larger ODP destroys more ozone than a gas with a smaller ODP. The ODP is calculated relative to CFC-11, which has an ODP defined to be 1. The calculations, which require the use of computer models that simulate the atmosphere, use as the basis of comparison the ozone depletion from an equal mass of each gas emitted to the atmosphere. Halon-1211 and halon-1301 have ODPs significantly larger than that of CFC-11 and most other chlorinated gases because bromine is much more effective (about 60 times) on a per-atom basis than chlorine in chemical reactions that destroy ozone. The gases with smaller values of ODP generally have shorter atmospheric lifetimes or contain fewer chlorine and bromine atoms.

Fluorine and iodine. Fluorine and iodine are also halogens. Many of the source gases in Figure Q6-1 also contain fluorine in addition to chlorine or bromine. After the source gases undergo conversion in the stratosphere (see Q5 ), the fluorine content of these gases is left in chemical forms that do not cause ozone depletion. As a consequence, halogen source gases that contain fluorine and no other halogens are not classified as ODSs. An important example of these are the HFCs, which are included in Table Q6-1 because they are common ODS substitute gases. HFCs have ODPs of zero and are also strong greenhouse gases, as quantified by a metric termed the Global Warming Potential (GWP) (see Q17 ). The Kigali Amendment to the Montreal Protocol now controls the production and consumption of some HFCs (see Q19 ), especially those HFCs with higher GWPs.

Iodine is a component of several gases that are naturally emitted from the oceans and some human activities. Although iodine can participate in ozone destruction reactions, iodine-containing source gases all have very short lifetimes. The importance for stratospheric ozone of very short-lived iodine containing source gases is an area of active research.

Other non-halogen gases. Other non-halogen gases that influence stratospheric ozone abundances have also increased in the stratosphere as a result of emissions from human activities (see Q20 ). Important examples are methane (CH 4 ) and nitrous oxide (N 2 O), which react in the stratosphere to form water vapor and reactive hydrogen, and nitrogen oxides, respectively. These reactive products participate in the destruction of stratospheric ozone (see Q1 ). Increased levels of atmospheric carbon dioxide (CO 2 ) alter stratospheric temperature and winds, which also affect the abundance of stratospheric ozone. Should future atmospheric abundances of CO 2 , CH 4 and N 2 O increase significantly relative to present day values, these increases will affect future levels of stratospheric ozone through combined effects on temperature, winds, and chemistry (see Figure Q20-3 ). Efforts are underway to reduce the emissions of these gases under the Paris Agreement of the United Nations Framework Convention on Climate Change because they cause surface warming (see Q18 and Q19 ). Although past emissions of ODSs still dominate global ozone depletion today, future emissions of N 2 O from human activities are expected to become relatively more important for ozone depletion as future abundances of ODSs decline (see Q20 ).

Table Q6-1. Atmospheric lifetimes, global emissions, Ozone Depletion Potentials, and Global Warming Potentials of some halogen source gases and HFC substitute gases.

a Includes both human activities (production and banks) and natural sources. Emissions are in units of kilotonnes per year (1 kilotonne = 1000 metric tons = 1 million (10 6 ) kilograms). These emission estimates are based on analysis of atmospheric observations and hence, for CFC-11, the unreported emissions recently noted (see Q15 ) are represented by the given range. The range of values for each emission estimate reflects the uncertainty in estimating emissions from atmospheric observations.

b 100-year GWP. ODPs and GWPs are discussed in Q17 . Values are calculated for emissions of an equal mass of each gas. ODPs given here reflect current scientific values and in some cases differ from those used in the Montreal Protocol.

Q7 What are the reactive halogen gases that destroy stratospheric ozone?

The chlorine- and bromine-containing gases that enter the stratosphere arise from both human activities and natural processes. When exposed to ultraviolet radiation from the Sun, these halogen source gases are converted to more reactive gases that also contain chlorine and bromine. Some reactive gases act as chemical reservoirs which can then be converted into the most reactive gases, namely ClO and BrO. These most reactive gases participate in catalytic reactions that efficiently destroy ozone.

Halogen-containing gases present in the stratosphere can be divided into two groups: halogen source gases and reactive halogen gases (see Figure Q7-1 ). The source gases, which include ozone-depleting substances (ODSs), are emitted at Earth’s surface by natural processes and by human activities (see Q6 ). Once in the stratosphere, the halogen source gases chemically convert at different rates to form the reactive halogen gases. The conversion occurs in the stratosphere instead of the troposphere for most gases because solar ultraviolet radiation (a component of sunlight) is more intense in the stratosphere (see Q2 ). Reactive gases containing the halogens chlorine and bromine lead to the chemical destruction of stratospheric ozone.

Reactive halogen gases. The chemical conversion of halogen source gases, which involves solar ultraviolet radiation and other chemical reactions, produces a number of reactive halogen gases. These reactive gases contain all of the chlorine and bromine atoms originally present in the source gases. The most important reactive chlorine- and bromine-containing gases that form in the stratosphere are shown in Figure Q7-1 . Throughout the stratosphere, the most abundant are typically hydrogen chloride (HCl) and chlorine nitrate (ClONO 2 ). These two gases are considered important reservoir gases because, while they do not react directly with ozone, they can be converted to the reactive forms that do chemically destroy ozone. The most reactive forms are chlorine monoxide (ClO) and bromine monoxide (BrO), and chlorine and bromine atoms (Cl and Br). A large fraction of total reactive bromine is generally in the form of BrO, whereas usually only a small fraction of total reactive chlorine is in the form of ClO. The special conditions that occur in the polar regions during winter cause the reservoir gases HCl and ClONO 2 to undergo nearly complete conversion to ClO in reactions on polar stratospheric clouds (PSCs) (see Q9 ).

Reactive chlorine at midlatitudes. Reactive chlorine gases have been observed extensively in the stratosphere using both local and remote measurement techniques. The measurements from space displayed in Figure Q7-2 are representative of how the amounts of chlorine-containing gases change between the surface and the upper stratosphere at middle to high latitudes. Total available chlorine (see red line in Figure Q7-2 ) is the sum of chlorine contained in halogen source gases (e.g., CFC-11, CFC-12) and in the reactive gases (e.g., HCl, ClONO 2 , and ClO). Available chlorine is constant to within about 10% from the surface to above 50 km (31 miles) altitude. In the troposphere, total chlorine is contained almost entirely in the source gases described in Figure Q6-1 . At higher altitudes, the source gases become a smaller fraction of total available chlorine as they are converted to the reactive chlorine gases. At the highest altitudes, available chlorine is all in the form of reactive chlorine gases.

In the altitude range of the ozone layer at midlatitudes, as shown in Figure Q7-2 , the reservoir gases HCl and ClONO 2 account for most of the available chlorine. The abundance of ClO, the most reactive gas in ozone depletion, is a small fraction of available chlorine. The low abundance of ClO limits the amount of ozone destruction that occurs outside of polar regions.

Reactive chlorine in polar regions. Reactive chlorine gases in polar regions undergo large changes between autumn and late winter. Meteorological and chemical conditions in both polar regions are now routinely observed from space in all seasons. Autumn and winter conditions over the Antarctic are contrasted in Figure Q7-3 using seasonal observations made near the center of the ozone layer (about 18 km (11.2 miles) altitude; see Figure Q11-3 ).

Ozone values are high over the entire Antarctic continent during autumn in the Southern Hemisphere. Temperatures are mid-range, HCl and nitric acid (HNO 3 ) are high, and ClO is very low. High HCl indicates that substantial conversion of halogen source gases has occurred in the stratosphere. In the 1980s and early 1990s, the abundance of reservoir gases HCl and ClONO 2 increased substantially in the stratosphere following increased emissions of halogen source gases. HNO 3 is an abundant, primarily naturally-occurring stratospheric compound that plays a major role in stratospheric ozone chemistry by both moderating ozone destruction and condensing to form PSCs, thereby enabling conversion of chlorine reservoirs gases to ozone-destroying forms. The low abundance of ClO indicates that little conversion of the reservoir gases occurs in the autumn, thereby limiting catalytic ozone destruction.

By late winter (September), a remarkable change in the composition of the Antarctic stratosphere has taken place. Low amounts of ozone reflect substantial depletion at 18 km altitude over an area larger than the Antarctic continent. Antarctic ozone holes arise from similar chemical destruction throughout much of the altitude range of the ozone layer (see altitude profile in Figure Q11-3 ). The meteorological and chemical conditions in late winter, characterized by very low temperatures, very low HCl and HNO 3 , and very high ClO, are distinctly different from those found in autumn. Low stratospheric temperatures occur during winter, when solar heating is reduced. Low HCl and high ClO reflect the conversion of the reactive halogen reservoir compounds, HCl and ClONO 2 , to the most reactive form of chlorine, ClO. This conversion occurs selectively in winter on PSCs, which form at very low temperatures (see Q9 ). Low HNO 3 is indicative of its condensation to form PSCs, some of which subsequently descend to lower altitudes through gravitational settling. High ClO abundances generally cause ozone depletion to continue in the Antarctic region until mid-October (spring), when the lowest ozone values usually are observed (see Q10 ). As temperatures rise at the end of the winter, PSC formation is halted, ClO is converted back into the reservoir species HCl and ClONO 2 (see Q9 ), and ozone destruction is curtailed.

Similar though less dramatic changes in meteorological and chemical conditions are also observed between autumn and late winter in the Arctic, where ozone depletion is less severe than in the Antarctic.

Reactive bromine observations. Fewer measurements are available for reactive bromine gases in the lower stratosphere than for reactive chlorine. This difference arises is in part because of the lower abundance of bromine, which makes quantification of its atmospheric abundance more challenging. The most widely observed bromine gas is BrO, which can be observed from space. Estimates of reactive bromine abundances in the stratosphere are larger than expected from the conversion of the halons and methyl bromide source gases, suggesting that the contribution of the very short-lived bromine-containing gases to reactive bromine must also be significant (see Q6 ).

Q8 What are the chlorine and bromine reactions that destroy stratospheric ozone?

Reactive gases containing chlorine and bromine destroy stratospheric ozone in “catalytic” cycles made up of two or more separate reactions. As a result, a single chlorine or bromine atom can destroy many thousands of ozone molecules before it leaves the stratosphere. In this way, a small amount of reactive chlorine or bromine has a large impact on the ozone layer. A special situation develops in polar regions in the late winter/early spring season, where large enhancements in the abundance of the most reactive gas, chlorine monoxide, lead to severe ozone depletion.

Stratospheric ozone is destroyed by reactions involving reactive halogen gases, which are produced in the chemical conversion of halogen source gases (see Figure Q7-1 ). The most reactive of these gases are chlorine monoxide (ClO), bromine monoxide (BrO), and chlorine and bromine atoms (Cl and Br). These gases participate in three principal reaction cycles that destroy ozone.

Cycle 1. Ozone destruction Cycle 1 is illustrated in Figure Q8-1 . The cycle is made up of two basic reactions: Cl + O 3 and ClO + O. The net result of Cycle 1 is to convert one ozone molecule and one oxygen atom into two oxygen molecules. In each cycle, chlorine acts as a catalyst because ClO and Cl react and are reformed. In this way, one Cl atom participates in many cycles, destroying many ozone molecules. For typical stratospheric conditions at middle or low latitudes, a single chlorine atom can destroy thousands of ozone molecules before it happens to react with another gas, breaking the catalytic cycle. During the total time of its stay in the stratosphere, a chlorine atom can thus destroy many thousands of ozone molecules.

Polar Cycles 2 and 3. The abundance of ClO is greatly increased in polar regions during late winter and early spring, relative to other seasons, as a result of reactions on the surfaces of polar stratospheric clouds (see Q7 and Q9 ). Cycles 2 and 3 (see Figure Q8-2 ) become the dominant reaction mechanisms for polar ozone loss because of the high abundances of ClO and the relatively low abundance of atomic oxygen (which limits the rate of ozone loss by Cycle 1). Cycle 2 begins with the self-reaction of ClO. Cycle 3, which begins with the reaction of ClO with BrO, has two reaction pathways that produce either Cl and Br or BrCl. The net result of both cycles is to destroy two ozone molecules and create three oxygen molecules. Cycles 2 and 3 account for most of the ozone loss observed in the stratosphere over the Arctic and Antarctic regions in the late winter/early spring season (see Q10 and Q11 ). At high ClO abundances, the rate of polar ozone destruction can reach 2 to 3% per day.

Sunlight requirement. Sunlight is required to complete and maintain these reaction cycles. Cycle 1 requires ultraviolet (UV) radiation (a component of sunlight) that is strong enough to break apart molecular oxygen into atomic oxygen. Cycle 1 is most important in the stratosphere at altitudes above about 30 km (18.6 miles), where solar UV-C radiation (100 to 280 nanometer (nm) wavelengths) is most intense (see Figure Q2-1 ).

Cycles 2 and 3 also require sunlight. In the continuous darkness of winter in the polar stratosphere, reaction Cycles 2 and 3 cannot occur. Sunlight is needed to break apart (ClO) 2 and BrCl, resulting in abundances of ClO and BrO large enough to drive rapid ozone loss by Cycles 2 and 3. These cycles are most active when sunlight returns to the polar regions in late winter/early spring. Therefore, the greatest destruction of ozone occurs in the partially to fully sunlit periods after midwinter in the polar stratosphere.

Sunlight in the UV-A (315 to 400 nm wavelengths) and visible (400 to 700 nm wavelengths) parts of the spectrum needed in Cycles 2 and 3 is not sufficient to form ozone because this process requires more energetic solar UV-C solar radiation (see Q1 and Q2 ). In the late winter/early spring, only UV-A and visible solar radiation is present in the polar stratosphere, due to low Sun angles. As a result, ozone destruction by Cycles 2 and 3 in the sunlit polar stratosphere during springtime greatly exceeds ozone production.

Other reactions. . Global abundances of ozone are controlled by many other reactions (see Q1 ). Reactive hydrogen and reactive nitrogen gases, for example, are involved in catalytic ozone-destruction cycles, similar to those described above, that also take place in the stratosphere. Reactive hydrogen is supplied by the stratospheric decomposition of water (H 2 O) and methane (CH 4 ). Methane emissions result from both natural sources and human activities. The abundance of stratospheric H 2 O is controlled by the temperature of the upper tropical troposphere as well as the decomposition of stratospheric CH 4 . Reactive nitrogen is supplied by the stratospheric decomposition of nitrous oxide (N 2 O), also emitted by natural sources and human activities. The importance of reactive hydrogen and nitrogen gases in ozone depletion relative to reactive halogen gases is expected to increase in the future because the atmospheric abundances of the reactive halogen gases are decreasing as a result of the Montreal Protocol, while abundances of CH 4 and N 2 O are projected to increase due to various human activities (see Q20 ).

Q9 Why has an “ozone hole” appeared over Antarctica when ozone-depleting substances are present throughout the stratosphere?

Ozone-depleting substances are present throughout the stratospheric ozone layer because they are transported great distances by atmospheric air motions. The severe depletion of the Antarctic ozone layer known as the “ozone hole” occurs because of the special meteorological and chemical conditions that exist there and nowhere else on the globe. The very low winter temperatures in the Antarctic stratosphere cause polar stratospheric clouds (PSCs) to form. Special reactions that occur on PSCs, combined with the isolation of polar stratospheric air in the polar vortex, allow chlorine and bromine reactions to produce the ozone hole in Antarctic springtime.

The severe depletion of stratospheric ozone in late winter and early spring in the Antarctic is known as the “ozone hole” (see Q10 ). The ozone hole appears over Antarctica because meteorological and chemical conditions unique to this region increase the effectiveness of ozone destruction by reactive halogen gases (see Q7 and Q8 ). In addition to a large abundance of these reactive gases, the formation of the Antarctic ozone hole requires temperatures low enough to form polar stratospheric clouds (PSCs), isolation from air in other stratospheric regions, and sunlight (see Q8 ).

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Ozone layer depletion: health and environmental effects

Introduction, effects on the skin, effects on the eyes, effects on the immune system, effects on the environment, so what do i do.

Ultraviolet ( UV ) radiation is divided into three categories of increasing energy: UV -A, UV -B and UV -C. UV -A is a low energy form of UV and has only minimal biological effects. UV -B, a higher energy form, causes the most damage to living organisms and materials. UV -C is absorbed by the oxygen in the atmosphere and never reaches us.

The ozone layer acts as a natural filter, absorbing most of the sun's burning ultraviolet ( UV ) rays. Stratospheric ozone depletion leads to an increase in UV -B that reach the earth's surface, where it can disrupt biological processes and damage a number of materials.

The fact that UV -B can cause biological effects is well demonstrated by the familiar sunburn that follows overexposure to the sun. However the health impacts of excessive exposure to UV -B go beyond just getting burned. Exposure to UV radiation has been linked to many human health problems, including skin cancer. Scientists also indicate that increased exposure to UV -B rays affects the human immune system and causes premature aging of the skin.

It is important to note, however, that UV -B radiation has always had these effects on humans. In recent years these effects have become more prevalent because Canadians are spending more time in the sun and are exposing more of their skin in the process. An increase in the levels of UV -B reaching the Earth as a result of ozone depletion may compound the effects that sun worshipping habits have already created.

Although fair-skinned, fair-haired individuals are at highest risk for skin cancer, the risk for all skin types increases with exposure to UV -B radiation. The effects of UV -B on the human immune system have been observed in people with all types of skin. There are three main types of skin cancer, basal cell carcinoma, squamous cell carcinoma, and malignant melanoma. Most cases of skin cancer in Canada are either basal or squamous cell carcinoma. Basal and squamous cell carcinomas progress slowly and rarely cause death because they usually don't spread to other parts of the body. These cancers are easily removed by surgery. Melanoma is the most serious and fortunately the least common form of skin cancer. Scientists strongly suspect that malignant melanoma, which can be fatal, is caused by exposure to UV light.

Scientists have confirmed that non-melanoma skin cancer is caused by UV -B radiation, and further believe that a sustained 10% depletion of the ozone layer would lead to a 26% percent increase in non-melanoma skin cancer. This could mean an additional 300,000 cases per year world wide.

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• Preventing skin cancer (Health Canada's It's Your Health page)

UV -B radiation can damage several parts of the eye, including the lens, the cornea, and the membrane covering the eye (conjunctiva). "Snow blindness" is the result of overexposure to UV -B and occurs in areas of the world with high levels of UV exposure, including snowy regions at high altitudes. Snow blindness is not unlike a sunburn, and if repeated, can cause damage to eye over the long term.

Cataracts are a clouding of the eye's lens and are the leading cause of permanent blindness world wide. They are a result of overexposure to UV . A sustained 10% thinning of the ozone layer is expected to result in nearly two million new cases of cataracts per year globally.

UV affects our ability to fight disease. The body's immune system is its first line of defense against invading germs. Recent research has shown that some viruses can be activated by increased exposure to UV .

Ultraviolet radiation not only affects humans, but wildlife as well. Excessive UV -B inhibits the growth processes of almost all green plants. There is concern that ozone depletion may lead to a loss of plant species and reduce global food supply. Any change in the balance of plant species can have serious effects, since all life is interconnected. Plants form the basis of the food web, prevent soil erosion and water loss, and are the primary producers of oxygen and a primary sink (storage site) for carbon dioxide.

UV -B causes cancer in domestic animals similar to those observed in humans. Although most animals have greater protection from UV -B because of their heavy coats and skin pigmentation, they cannot be artificially protected from UV -B on a large scale. Eyes and exposed parts of the body are most at risk.

• Keep sun exposure to a minimum, especially between the hours of 10:00 a.m. and 3:00 p.m. when the sun's rays are the most intense.
• Wear wide-brimmed hats, UV -B blocking sunglasses, and long-sleeved shirts and pants.
• Wear sunscreen with a Sun Protection Factor (SPF) of 15 or greater on any exposed skin. Reapply every hour or after swimming or strenuous activity.

Although the ozone layer is the one constant defense against UV penetration, several other factors can have an effect:

Latitude . Since the sun's rays impact the Earth's surface at the most direct angle over the equator they are the most intense at this latitude.

Season . During winter months, the sun's rays strike at a more oblique angle than they do in the summer. This means that all solar radiation travels a longer path through the atmosphere to reach the Earth, and is therefore less intense.

Time of day . Daily changes in the angle of the sun influence the amount of UV radiation that passes through the atmosphere. When the sun is low in the sky, its rays must travel a greater distance through the atmosphere and may be scattered and absorbed by water vapour and other atmospheric components. The greatest amount of UV reaches the Earth around midday when the sun is at its highest point.

Altitude . The air is thinner and cleaner on a mountaintop - more UV reaches there than at lower elevations.

Cloud cover . Clouds can have a marked impact on the amount of UV radiation that reaches the Earth's surface; generally, thick clouds block more UV than thin cloud cover.

Rain . Rainy conditions reduce the amount of UV transmission.

Air pollution . Much as clouds shield the Earth's surface from UV radiation, urban smog can reduce the amount of UV radiation reaching the Earth.

Land Cover . Incoming UV radiation is reflected from most surfaces. Snow reflects up to 85 per cent, dry sand and concrete can reflect up to 12 per cent. Water reflects only five per cent. Reflected UV can damage people, plants, and animals just as direct UV does.

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Ozone Depletion

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Ozone depletion is the term used to describe two separate but related phenomena that have been observed: a stable reduction in the total ozone concentration in the stratosphere (also known as the ozone layer) and a much more significant reduction in springtime in stratospheric ozone around the polar regions of the earth. The ozone hole is the name given to the latter phenomenon. The most crucial process in both is the catalytic destruction of ozone by atomic halogens, although the specifics of ozone-hole development in the pole regions differs from those of mid-latitude thinning. The photodissociation of anthropogenic halocarbon refrigerants, propellants, solvents, and foam-blowing agents, including chlorofluorocarbons (CFCs) and others, are the primary sources of halogen atoms released in the stratosphere. After being released at the surface, winds carry these substances into the stratosphere. As halocarbon emissions rise, so do both types of ozone depletion. In the past two decades,...

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(2024). Ozone Depletion. In: Dictionary of Toxicology. Springer, Singapore. https://doi.org/10.1007/978-981-99-9283-6_2034

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