The ozone layer sits in the stratosphere between 15 km and 30 km above the earth. It absorbs most of the sun's ultraviolet radiation (UV-B), limiting the amount of this radiation that reaches the surface of the Earth. Because this radiation causes skin cancer and cataracts, the ozone layer plays an important role in protecting human health. It also prevents radiation damage to plants, animals, and materials.
In the 1970s, scientists noticed that the ozone layer was thinning. Researchers found evidence that linked the depletion of the ozone layer to the presence of chlorofluorocarbons (CFCs) and other halogen-source gases in the stratosphere. Ozone-depleting substances (ODS) are synthetic chemicals, which were used around the world in a wide range of industrial and consumer applications. The main uses of these substances were in refrigeration and air conditioning equipment and in fire extinguishers. Other important uses included aerosol propellants, solvents and blowing agents for insulation foams.
To halt the depletion of the ozone layer, countries around the world agreed to stop using ozone-depleting substances. This agreement was formalised in the Vienna Convention for the Protection of the Ozone Layer in 1985 and the Montreal Protocol on Substances that Deplete the Ozone Layer in 1987. In 2009, the Vienna Convention and the Montreal Protocol became the first treaties in the history of the United Nations to achieve universal ratification. Substances covered by the protocol are referred to as 'controlled substances'. The main substances include chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), halons, carbon tetrachloride, methyl chloroform and methyl bromide. The damage to the ozone layer caused by each of these substances is expressed as their ozone depletion potential (ODP).
These international agreements helped to greatly reduce the worldwide use of ozone-depleting substances in Europe and around the World (Figure 1). Scientific monitoring shows signs that the ozone layer is starting to recover. Full recovery is not expected to occur before the middle of the 21st century.
The reduction in ozone-depleting substances has also had a beneficial side-effect. Ozone-depleting substances are also very potent greenhouse gases, contributing to the phenomenon as other substances widely known to have a greenhouse effect like carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). Therefore, by reducing emissions of ozone-depleting substances, the Montreal Protocol has protected both the ozone layer and the climate at the same time.
The reduction of ODS emissions is not a uniformly positive story. In fact it has indirectly led to new problems. Fluorinated gases (F-gases) have been introduced as substitutes for ODS in many sectors such as refrigeration and air conditioning applications. F-gases include hydrofluorocarbons (HFCs), perfluorocarbons (PFCs) and sulphur hexafluoride (SF6). These gases do not deplete the ozone layer, but they are greenhouse gases. This means that these new gases also contribute to climate change. And to make matters worse, these F-gases often have a far larger impact on the climate than 'traditional' greenhouse gases such as carbon dioxide (CO2). For example, some F-gases have a greenhouse effect that is up to 23 000 times more powerful than the same amount of carbon dioxide. Fortunately, the emissions of F-gases are far smaller than those of CO2, but the use of F-gases and their presence in the atmosphere have increased since the 1990s. As a result, the significant contribution of the Montreal Protocol to fighting climate change is in danger of being wiped out by the growing importance of F-gas emissions.
Because F-gases contribute to climate change, businesses are now looking to replace them with other substances. Alternatives that do not damage the ozone layer or contribute to climate change have become available over recent years in a variety of applications such as refrigeration, air conditioning, foam blowing and aerosols. Many of these alternatives lead also to higher energy efficiency which is important as the indirect emissions from energy use during the lifespan of a product are often considerably higher than direct emissions of F-gases.
Million to OneCompared to other gases in the atmosphere, ozone is pretty rare. According to NOAA, there are only about three molecules of ozone for every ten million molecules of air.
Source: Figure Q3-1 from Michaela I. Hegglin (Lead Author), David W. Fahey, Mack McFarland, Stephen A. Montzka, and Eric R. Nash, Twenty Questions and Answers About the Ozone Layer: 2014 Update, Scientific Assessment of Ozone Depletion: 2014, 84 pp., World Meteorological Organization, Geneva, Switzerland, 2015. Because all sunlight contains some UVB, even with normal stratospheric ozone levels, it is always important to protect your skin and eyes from the sun. See a more detailed explanation of health effects linked to UVB exposure.
Phytoplankton form the foundation of aquatic food webs. Phytoplankton productivity is limited to the euphotic zone, the upper layer of the water column in which there is sufficient sunlight to support net productivity. Exposure to solar UVB radiation has been shown to affect both orientation and motility in phytoplankton, resulting in reduced survival rates for these organisms. Scientists have demonstrated a direct reduction in phytoplankton production due to ozone depletion-related increases in UVB.
Increases in UVB radiation could affect terrestrial and aquatic biogeochemical cycles, thus altering both sources and sinks of greenhouse and chemically important trace gases (e.g., carbon dioxide, carbon monoxide, carbonyl sulfide, ozone, and possibly other gases). These potential changes would contribute to biosphere-atmosphere feedbacks that mitigate or amplify the atmospheric concentrations of these gases.
Another group of substances, hydrofluorocarbons (HFCs), were introduced as non-ozone depleting alternatives to support the timely phase-out of CFCs and HCFCs. HFCs are now widespread in air conditioners, refrigerators, aerosols, foams and other products. While these chemicals do not deplete the stratospheric ozone layer, some of them have high GWPs ranging from 12 to 14,000. Overall HFC emissions are growing at a rate of 8% per year and annual emissions are projected to rise to 7-19% of global CO2 emissions by 2050. Uncontrolled growth in HFC emissions, therefore, challenges efforts to keep global temperature rise at or below 2C this century. Urgent action on HFCs is needed to protect the climate system.
With the full and sustained implementation of the Montreal Protocol, the ozone layer is projected to recover by the middle of this century. Without this treaty, ozone depletion would have increased tenfold by 2050 compared to current levels, and resulted in millions of additional cases of melanoma, other cancers and eye cataracts. It has been estimated, for example, that the Montreal Protocol is saving an estimated two million people each year by 2030 from skin cancer.
The ozone layerozone layerThe region of the stratosphere containing the bulk of atmospheric ozone. The ozone layer lies approximately 15-40 kilometers (10-25 miles) above the Earth's surface, in the stratosphere. Depletion of this layer by ozone depleting substances (ODS) will lead to higher UVB levels, which in turn will cause increased skin cancers and cataracts and potential damage to some marine organisms, plants, and plastics. The science page ( ) offers much more detail on the science of ozone depletion. is a concentration of ozone molecules in the stratospherestratosphereThe region of the atmosphere above the troposphere. The stratosphere extends from about 10km to about 50km in altitude. Commercial airlines fly in the lower stratosphere. The stratosphere gets warmer at higher altitudes. In fact, this warming is caused by ozone absorbing ultraviolet radiation. Warm air remains in the upper stratosphere, and cool air remains lower, so there is much less vertical mixing in this region than in the troposphere.. About 90 percent of the planet's ozone is in the ozone layer. The layer of the Earth's atmosphere that surrounds us is called the tropospheretroposphereThe region of the atmosphere closest to the Earth. The troposphere extends from the surface up to about 10 km in altitude, although this height varies with latitude. Almost all weather takes place in the troposphere. Mt. Everest, the highest mountain on Earth, is only 8.8 km high. Temperatures decrease with altitude in the troposphere. As warm air rises, it cools, falling back to Earth. This process, known as convection, means there are huge air movements that mix the troposphere very efficiently.. The stratosphere, the next higher layer, extends about 6 to 31 miles (or 10 to 50 kilometers) above the Earth's surface. Learn more about the ozone layer.
Stratospheric ozone is a naturally occurring gas that filters the sun's ultraviolet (UVUVUltraviolet radiation is a portion of the electromagnetic spectrum with wavelengths shorter than visible light. The sun produces UV, which is commonly split into three bands: UVA, UVB, and UVC. UVA is not absorbed by ozone. UVB is mostly absorbed by ozone, although some reaches the Earth. UVC is completely absorbed by ozone and normal oxygen. NASA provides more information on their web site ( ).) radiation. A diminished ozone layer allows more UV radiation to reach the Earth's surface. For people, overexposure to UV rays can lead to skin cancer, cataracts, and weakened immune systems. Increased UV can also lead to reduced crop yield and disruptions in the marine food chain. Learn about the health and environmental effects of ozone layer depletion.
Ozone molecules in the stratosphere are constantly being produced and destroyed by different types of UV radiation from the sun. Normally, the production and destruction is balanced, so the amount of ozone in the stratosphere at any given time is stable. However, scientists have discovered that certain chemicals react with UV radiation in the stratosphere, which causes them to break apart and release chlorine or bromine atoms. These atoms, in turn, destroy ozone molecules. 153554b96e