What do chlorofluorocarbons do

This ozone loss was described in by British researcher Joe Farman and his colleagues 3. The ozone hole was different than ozone loss in the midlatitudes. Ozone loss also is enhanced in polar regions as a result of reactions involving polar stratospheric clouds PSCs 5 and in midlatitudes following volcanic eruptions. The need for controlling the CFCs became urgent. This international agreement included restrictions on production of CFC, , , , , and the Halons chemicals used as a fire extinguishing agents.

An amendment approved in London in was more forceful and called for the elimination of production by the year The environmental concern for CFCs follows from their long atmospheric lifetime 55 years for CFC and years for CFC, CCl 2 F 2 9 which limits our ability to reduce their abundance in the atmosphere and associated future ozone loss. This resulted in the Copenhagen Amendment that further limited production and was approved later in The manufacture of these chemicals ended for the most part on January 1, The only exceptions approved were for production within developing countries and for some exempted applications in medicine i.

The Montreal Protocol included enforcement provisions by applying economic and trade penalties should a signatory country trade or produce these banned chemicals.

A total of signatory countries have now signed the Montreal Protocol. Atmospheric measurements CFC and CFC reported in showed that their growth rates were decreasing as result of both voluntary and mandated reductions in emissions 9. Many CFCs and selected chlorinated solvents have either leveled off Figure 1 or decreased in concentration by 9, The demand for the CFCs was accomodated by recycling, and reuse of existing stocks of CFCs and by the use of substitutes.

Some applications, for example degreasing of metals and cleaning solvents for circuit boards, that once used CFCs now use halocarbon-free fluids, water sometimes as steam , and diluted citric acids. The HCFCs include hydrogen atoms in addition to chlorine, fluorine, and carbon atoms.

The advantage of using HCFCs is that the hydrogen reacts with tropospheric hydroxyl OH , resulting in a shorter atmospheric lifetime. HCFC CHClF 2 has an atmospheric lifetime of about 13 years 11 and has been used in low-demand home air-conditioning and some refrigeration applications since However, HCFCs still contain chlorine which makes it possible for them to destroy ozone.

The Copenhagen amendment calls for their production to be eliminated by the year The HFCs are considered one of the best substitutes for reducing stratospheric ozone loss because of their short lifetime and lack of chlorine.

Use of the CFCs, some chlorinated solvents, and Halons should become obsolete in the next decade if the Montreal Protocol is observed by all parties and substitutes are used. The science that became the basis for the Montreal Protocol resulted in the Nobel Prize for Chemistry.

The prize was awarded jointly to Professors F. 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. Ozone was also measured by instruments on satellites orbiting Earth, though satellite technology in the mids was still rather primitive. The crucial evidence supporting the CFC hypothesis came from British scientists working at the Halley Bay Station of the British Antarctic Survey, who had been taking ground-based measurements of total ozone for decades.

About half of bromine entering the stratosphere is from man-made sources, mostly Halons. While acting to destroy ozone, CFCs and HCFCs also act to trap heat in the lower atmosphere, causing the earth to warm and climate and weather to change.

Taken together greenhouse gases are expected to warm the planet by 2. Some effects of global climate change include:. Use of CFCs is restricted to equipment placed into use prior to The ozone layer in the stratosphere shields life on Earth from most UV-B and UV-C, the most harmful varieties of ultraviolet radiation. Credit: NASA. Ozone and oxygen molecules are constantly being formed, destroyed, and reformed in the ozone layer as they are bombarded by ultraviolet radiation UV , which breaks the bonds between atoms, creating free oxygen atoms.

Free oxygen atoms are highly reactive, meaning that they bond easily with other molecules. If a free oxygen atom bumps into an oxygen molecule O 2 , it will form ozone O 3. If a free oxygen atom bumps into another oxygen atom, it will form an oxygen molecule O 2.

British scientists at Halley Bay, Antarctica, thought their instruments were malfunctioning when they started recording low ozone amounts in the ozone layer above Antarctica in They had been measuring ozone in the Antarctic atmosphere since and had never before seen the levels drop so much.

Why would ozone levels have dropped? Could it just be natural variation? Since ozone concentrations over this region often vary from season to season, the researchers weren't concerned, but record low ozone levels kept occurring nearly every spring. No one knew why.