The crystals provide a surface for a chemical reaction that changes chlorine in molecules that do not affect ozone such as hydrogen chloride into more active forms that do destroy ozone. A colder winter will result in more extensive polar stratospheric clouds, greater destruction of ozone, and a larger ozone hole. Left : An illustration showing the layers of the atmosphere. Most of the protective ozone layer lies in the stratosphere, while nearly all weather occurs in the troposphere.
Increases in the amount of carbon dioxide in the atmosphere can also create this same effect, noted Dr. While higher carbon dioxide concentrations are thought to cause a warming of the atmosphere's lowest layer the troposphere , scientists know that this same carbon dioxide actually causes the stratosphere to cool down. This cooling can exacerbate ozone destruction just as a particularly cold winter does.
The cold air over Antarctica in winter creates a huge "whirlpool" of fast-moving air circling Antarctica called the "Antarctic vortex. It locks in that body of air and it keeps the outside high-ozone air from coming in," McPeters said. Most stratospheric ozone is created in the tropics, because the intensity of the solar radiation that causes formation of ozone is higher nearer the equator. The ozone is then transported by stratospheric air currents to the Arctic and to Antarctica.
The strong and stable vortex prevents the migration of ozone into the stratosphere over Antarctica, exacerbating the low levels caused by the ice crystal-catalyzed destruction of ozone. By virtually sealing Antarctica off from the warmer air surrounding it, the vortex causes temperatures in Antarctica to drop even lower.
Lower temperatures cause the formation of more ice-crystal clouds and the destruction of even more ozone. Then toward the end of the spring the vortex breaks down, and over the summer there really isn't a vortex. And then it sets up again the next fall. The relative warmth of the Arctic is the main reason why a similar ozone hole doesn't form over the North Pole. Right : Images from a NASA satellite showing ozone levels over the Arctic top and the Antarctic bottom at similar points in each hemisphere's seasons.
Blue indicates low ozone and red indicates high ozone. The research described in the short paper, however, fell like a scientific bombshell, one whose repercussions would be felt around the world. It also led to F. Sherwood Rowland and Mario J. Crutzen of the Max Plank Institute for Chemistry, Mainz, another pioneer in stratospheric ozone research. That stratospheric ozone absorbs ultraviolet radiation that otherwise would reach the surface of Earth.
At the time, CFCs were in wide use in refrigeration, air conditioning and aerosol spray cans. The compounds are inert and essentially nontoxic, characteristics that made them well-suited for these applications.
These same characteristics, however, also made them a danger to life on Earth. Commemorative Booklet PDF. In the s, refrigeration and air conditioning systems used compounds such as ammonia, chloromethane, propane and sulfur dioxide as refrigerants. Though effective, the compounds were toxic and flammable, and exposure to them could result in serious injury or death. A team of chemists at Frigidaire led by Thomas Midgely Jr.
The team focused their effort on compounds containing carbon and halogens such as fluorine and chlorine. Such compounds were known to be volatile and chemically inert, both important properties for the team studying their use in refrigeration.
Chlorofluoromethanes are being added to the environment in steadily increasing amounts. These compounds are chemically inert and may remain in the atmosphere for years, and concentrations can be expected to reach 10 to 30 times present levels.
Photodissociation of the chlorofluoromethanes in the stratosphere produces significant amounts of chlorine atoms, and leads to the destruction of atmospheric ozone. From an environmental standpoint, ozone is a confusing molecule.
But in the stratosphere, the region of the atmosphere from 6 to 31 miles, ozone absorbs potentially damaging ultraviolet UV radiation. Without a protective ozone layer in the atmosphere, animals and plants could not exist, at least not upon land. Lovelock had measured trichlorofluoromethane CFC in the atmosphere in amounts that suggested that practically all of the CFC ever manufactured was still present in the atmosphere.
Rowland decided to devote a portion of his research to understanding the fate of CFCs in the atmosphere. Although CFCs are inert in the lower troposphere, Rowland realized that they can be broken down by UV radiation once they drift up into the stratosphere. Each chlorine atom would react immediately with an ozone molecule, setting off a chain reaction that would destroy thousands of ozone molecules.
In their paper, they estimated that if CFC use was banned immediately, ozone loss would go on for years. If CFC production continued, however, ozone loss would be even greater. In , the National Academies of Science issued a report affirming the destructive effects of CFCs on stratospheric ozone. Congressional hearings reached similar conclusions, and states and the federal government began exploring bans on the use of CFCs in aerosol cans.
Gases such as CFCs that do not dissolve in water and that are relatively unreactive in the lower atmosphere are mixed relatively quickly and therefore reach the stratosphere regardless of their weight.
Measured changes in the concentration of constituents versus altitude teach us more about the fate of compounds in the atmosphere. For example, the two gases carbon tetrafluoride CF 4 , produced mainly as a by-product of the manufacture of aluminum and CFC CCl 3 F, used in a variety of human activities are both heavier than air.
Carbon tetrafluoride is completely unreactive at altitudes up to at least 50 kilometers in the atmosphere.
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