Aura MLS observations of unprecedented Arctic ozone loss. Destruction of Arctic Ozone during the Winter. Ozone Aura instruments are closely monitoring the ozone layer. But I thought that ozone is "bad"?! Wear your sunscreen! Wear your hat!
All these substances are also greenhouse gases. See hydrochlorofluorocarbons, hydrofluorocarbons, perfluorocarbons, ozone depleting substance. CFCs and hydrofluorocarbons hydrofluorocarbons Compounds containing only hydrogen, fluorine, and carbon atoms.
They were introduced as alternatives to ozone depleting substances in serving many industrial, commercial, and personal needs. HFCs are emitted as by-products of industrial processes and are also used in manufacturing. They do not significantly deplete the stratospheric ozone layer, but they are powerful greenhouse gases with global warming potentials ranging from HFCa to 11, HFC HCFCs , were once used widely in refrigerants, insulating foams, solvents, and other applications.
These substances all release chlorine atoms into the stratosphere. A single chlorine atom can break apart more than , ozone molecules. Other chemicals that damage the ozone layer include methyl bromide methyl bromide A compound consisting of carbon, hydrogen, and bromine.
Methyl Bromide is an effective pesticide used to fumigate soil and many agricultural products. Because it contains bromine, it depletes stratospheric ozone and has an ozone depletion potential of 0. Production of methyl bromide was phased out on December 31, , except for allowable exemptions. They are generally used as fire extinguishing agents and cause ozone depletion. Bromine is many times more effective at destroying stratospheric ozone than chlorine. See ozone depleting substance.
Methyl chloroform is used as an industrial solvent. Its ozone depletion potential is 0. As methyl bromide and halons are broken apart, they release bromine atoms, which are 60 times more destructive to ozone molecules than chlorine atoms.
Atmospheric levels of these ODS rapidly increased before the implementation of the Montreal Protocol on Substances that Deplete the Ozone Layer and its subsequent revisions and amendments. However, the atmospheric levels of nearly all of these substances have declined substantially in the past two decades. The ozone layer acts as an invisible shield and protects us from harmful ultraviolet UV radiation from the sun. In particular, the ozone layer protects us from the UV radiation, known as UV-B, which causes sunburn.
Long-term exposure to high levels of UV-B threatens human health and damages most animals, plants and microbes, so the ozone layer protects all life on Earth. Ozone absorbs UV-B radiation from the sun. When an ozone molecule absorbs UV-B, it comes apart into an oxygen molecule O 2 and a separate oxygen atom O.
Later, the two components can reform the ozone molecule O 3. Ozone is being produced and destroyed all the time. When UV-C light reaches the stratosphere, it is completely absorbed by oxygen molecules and never reaches the Earth's surface. UV-C splits oxygen molecules into oxygen atoms. These single atoms then react with other oxygen molecules to produce ozone. So, these reactions increase the amount of ozone in the stratosphere.
But, ozone is not the only gas in the stratosphere. Other gases containing nitrogen and hydrogen are also in the stratosphere and participate in reaction cycles that destroy ozone converting it back into oxygen. So, these reactions decrease the amount of ozone in the stratosphere. When undisturbed, the balance between the natural processes of ozone production and destruction maintains a consistent ozone concentration in the stratosphere. Unfortunately, we, humans do not leave this natural process undisturbed….
In the mids, scientists realised that the ozone layer was threatened by the accumulation of gases containing halogens chlorine and bromine in the atmosphere. Manmade chemicals containing halogens were determined to be the main cause of ozone loss.
These chemicals are collectively known as ozone-depleting substances ODSs. The most important ODSs were chlorofluorocarbons CFCs , which at one time were widely used in air conditioners, refrigerators, aerosol cans, and in inhalers used by asthma patients.
Other chemicals, such as hydrochlorofluorocarbons HCFCs , halons and methyl bromide also deplete the ozone layer. Most of our computers, electronics and parts of our appliances were cleaned with ozone-depleting solvents.
Offices, computer facilities, military bases, airplanes and ships extensively used halons for fire protection. A lot of the fruit and vegetables we ate were fumigated by methyl bromide to kill pests. When a CFC molecule reaches the stratosphere, it eventually absorbs UV radiation, causing it to decompose and release its chlorine atoms.
One chlorine atom can destroy up to , ozone molecules. Too many of these chlorine and bromine reactions disrupt the delicate chemical balance that maintains the ozone layer, causing ozone to be destroyed faster than it is created. Because of the Montreal Protocol, we have avoided a world where severe ozone holes would have occurred every year over the Arctic and Antarctic. By the mid st century, severe ozone depletion would have spread across the planet, including the tropics.
But how large an increase in UV-B would have resulted from uncontrolled ozone depletion? And how would increased UV-B have affected people, food production, ecosystems and even construction materials? Levels of UV-B radiation are higher in the tropics than at temperate or polar latitudes, and higher at high altitude than at sea level. UV-B also varies predictably with season at temperate and high latitudes UV-B reaches its maximum in mid-summer , and with time of day peak levels occurring around mid-day.
Variation in cloud also has large effects. Even with the Montreal Protocol to protect the ozone layer, we should all try to avoid too much exposure to the sun to reduce the risk of disease such as skin cancer and cataracts that are cause by overexposure to UV-B radiation.
Figure 1: U. This map depicts ozone concentrations by U. All orange, red, and purple areas exceeded the 8-hour ambient air quality standard for ozone during The map illustrates how likely it may be for a particular area to experience air quality advisories for ozone.
Ozone has two properties of interest to human health. First, it absorbs UV light, reducing human exposure to harmful UV radiation that causes skin cancer and cataracts. Second, when inhaled, it reacts chemically with many biological molecules in the respiratory tract, leading to a number of adverse health effects.
This course addresses this second property. Review Key Points. Skip to main content.
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