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Subscriber Exclusive Content. Why are people so dang obsessed with Mars? How viruses shape our world. The era of greyhound racing in the U. See how people have imagined life on Mars through history. See More. 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. When Rowland lectured on CFCs, industry groups often released statements disputing his claims.
It seemed that, because of his focus on CFCs and ozone depletion, he started getting fewer invitations to speak. That bothered him. Rowland and Molina and the other scientists trying to understand stratospheric chemistry faced serious and fundamental challenges.
A significant number of chemical species were clearly involved in the interaction of CFCs and ozone in the stratosphere. Most are highly reactive and present in only trace amounts. Their chemistry was difficult to replicate in the laboratory. Additionally, stratospheric ozone concentrations fluctuate naturally by geography and by season.
The stratosphere is not an easy place to do research in. Measurements of ozone concentration were carried out by instruments carried into the stratosphere by balloons and aircraft. Of the three types of UV radiation, UVB is the most harmful because it reaches the furthest, even beneath the ocean's surface.
Chlorofluorocarbons, or CFCs, are compounds made up of combinations of the elements chlorine, fluorine and carbon; aerosols, refrigerants and foams contain CFCs. When these CFCs enter the air, they rise up into the atmosphere to meet up with and destroy ozone molecules.
Some of the better-known CFCs are the Freon compounds, which were used as cooling ingredients in refrigerators and air conditioners but have since been phased out of production in the United States.
The U. Environmentally friendly compounds have mostly replaced Freon as refrigerants. These chlorine atoms wander around the atmosphere until they meet up with ozone molecules. The chlorine atom and one of the oxygen atoms of ozone combine, leaving behind diatomic, or molecular, oxygen. When a free oxygen atom contacts this chlorine-oxygen compound, the two oxygen atoms combine to form molecular oxygen, and the chlorine goes off to devastate more ozone molecules.
Molecular oxygen, unlike ozone molecules, cannot keep UV rays from reaching the Earth's surface. Environmental Protection Agency estimates that one atom of chlorine can destroy as many as , molecules of ozone. In , M. Molina and F. Rowland published a paper outlining how CFCs broke down ozone molecules in the atmosphere.
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