What are CFCs

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http://youtube.com/watch?v=YL9g7JGLPp4

This video is a brief introduction to CFCs. • What are CFCs? • When did CFCs first start being used? • What were CFCs used for? • Why aren't CFCs being used anymore? • How are concentrations of CFCs in the atmosphere changing? • For more information see: • https://en.wikipedia.org/wiki/Chlorof... • This video is part of a playlist: The Ozone Hole • The Ozone Hole • The previous videos in this series are: • 1. The Layers of the Atmosphere: • Layers of the atmosphere • 2. The Ozone Layer: • Видеоклип • 3. CFC numbering system: • How to work out the chemical formula ... • Video Script: • Okay so first of all, CFC stand for chlorofluorocarbons and these are compounds that contain chlorine, fluorine and carbon. • They are also sometimes called Freon's because that’s the trade name DuPont used for them and DuPont is the chemical company that first produced them. • CFCs are a type of halocarbon and halocarbons are any compounds that contain halogens and carbon. And halogens are elements in the 17th column in the periodic table, the most common ones being fluorine, chlorine, bromine and iodine. • They are industrially produced compounds with low toxicity, low reactivity and low flammability so they are not directly dangerous to humans and they use to be very popular and widely used. • They were first invented by a Belgian scientist (Frédéric Swarts) in the 1890s who managed to replace chloride in carbon tetrachloride (CCl4) with fluoride to make CFC-11 (CCl3F) and CFC-12 (CCl2F2). • In the late 1920s, Thomas Midgley, Jr. improved the process of synthesis and led the effort to use CFC as a refrigerant to replace ammonia (NH3), chloromethane (CH3Cl), and sulfur dioxide (SO2), which were commonly used at the time but are toxic. He demonstrated their safety and in flammability by inhaling a mouthful of the gas and using it to blow out a candle. DuPont began producing CFCs commercially in the 1930's and they first began to be used on a large scale in the 1960s and 70s. • CFCs are usually made by halogen exchange of chlorinated methane's and ethane's. Pretty much every possible kind of CFC has been made by this point and they were tested and the ones that were useful were mass produced. • CFCs were most commonly used in refrigerants, aerosol propellants, solvents, and foam blowing agents. • Because CFCs are so unreactive they take a long time to be broken down in the atmosphere and therefore they are very long lived compounds and have atmospheric lifetimes of decades or centuries. For example CFC-11 has a lifetime of about 35 to 89 years and CFC-115 has a lifetime of about 404 to 813 years. • Also CFCs are trace gases in the atmosphere which means that they have very low concentrations, on the order of parts per trillion. • However despite their small concentrations they can have a large impact in the atmosphere. Because CFCs are so unreactive they aren’t broken down in the troposphere, the lowest layer of the atmosphere. They can only be broken down by strong UV radiation which they are exposed to when they reach the stratosphere, the next layer in the atmosphere. Here they break down to form chlorine free radicals which catalyst ozone destruction and this has led to the formation of the ozone hole. • Because of this there was an international agreement in 1989 called the Montreal Protocol to phase of the use of CFCs and other ozone depleting substances. • Under the Montreal Protocol developed countries stopped producing CFCs in 1996 and developing countries stopped producing CFCs in 2010 with very few critical use exceptions. • This has been relatively successful as CFCs have mostly been replaced by other compounds called HCFCs and atmospheric concentrations of a lot of the major CFCs have stabilised out and some have even started to decrease. So while this problem hasn’t been fixed it is on the mend. • There are only very small emissions of CFCs still being released. These emissions are almost all coming from source banks which are stores of CFCs that were made before the ban started and from recycling of CFCs to reuse ones that have already been made and release of CFCs from products that were made before the ban. It is expected that these remaining sources will gradually decrease over time and that concentrations of CFCs will continue to decrease in the atmosphere.

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