Freons release into atmosphere

The chlorine atoms in the upper atmosphere come from the breakdown of CF2 CI2 and other similar chlorofluorocarbons (CFCs), known commercially as Freons. Production of these compounds was more than one million tons in 1988, largely for use in relrigerators and air conditioners. Once released into the atmosphere, CFCs diffuse slowly upward in the atmosphere until they reach the ozone layer. There, ultraviolet light Irom the sun splits off chlorine atoms. These react with ozone, with dramatic results. Annual ozone decreases have exceeded 50% above Antarctica. The background photo shows the Antarctic hole (red-violet) on September 24, 2003. 

Chlorofluorocarbon (CFC) compounds (Freons ) are important tracers of ocean circulation. Since CFC-11 and CFC-12 were released at different rates, their concentrations as well as their ratios can be used to determine when a water mass left contact with the sea surface over the 50 years since Freons were released into the atmosphere and taken up by the ocean. CFC-113 and carbon tetrachloride are being investigated as additional tracers. Picomole levels of CFCs dissolved in seawater are determined using a gas chromatograph equipped with an electron capture detector. The World Ocean Circulation Experiment (WOCE) Hydrographic Program calls for measurements with a precision and accuracy of 1% and a detection limit of... 

In summary, if organic compounds can see solar radiation either in surface water or in the atmosphere, there are many mechanisms that can result in their transformation. The hydroxyl radical is extremely versatile and any compound with a C—H bond may react by this process. In a sense, these processes are a mixed blessing in that on the one hand compounds emitted in significant amounts react to produce a major impact on air quality. By contrast, these processes are probably the most efficient in the degradation of compounds released into the environment. Those compounds that react slowly or not at all, such as the freons and methane, can contribute to global impacts. The significance of these transformation processes is obvious. 

The reaction shown below is used to destroy Freon-12 (CF2CI2), preventing its release into the atmosphere. What mass of NaF will be formed if 250.0 kg of CF2CI2 and 400.0 kg of Na2C204 are heated and allowed to react to completion ... 

The critical point refers to the certain combination of temperature and pressure at which the liquid density is equal to the vapor density. At its critical point, liquid will become vapor and is easily removed. We cannot directly remove water using its critical point because the temperature and pressure of the critical point (374°C and 22 MPa) are too high and may damage the specimen. Alternatively, we can replace water with a transitional fluid that has a critical point with lower temperature and pressure. Liquid CO2 or Freon is often used as the transitional fluid. The critical point for liquid CO2 is 31.1 °C and 7.4 MPa. The common procedure is described as follows. First, water content in a specimen is removed by dehydration with an ethanol series (30, 50, 75 and 100%). Then, the dehydrated specimen is transferred into an ethanol-filled and cooled chamber in the critical-point drying apparatus. The transitional fluid is introduced until it completely displaces ethanol in the chamber. The chamber is gradually heated and pressurized to reach the critical point of the transitional fluid. After reaching the critical point, the transitional fluid vaporizes, and this vapor is slowly released from the chamber until atmospheric pressure is reached. Then, we can retrieve the intact, dry specimen from the chamber. 

A carbon atom can be bonded to as many as four halogen atoms, so an enormous number of organic halides can exist. Completely fluorinated compounds are known as fluorocarbons or sometimes perfluorocarbons. The fluorocarbons are even less reactive than hydrocarbons. Saturated compounds in which all H atoms have been replaced by some combination of Cl and F atoms are called chlorofluorocarbons or sometimes freons. These compounds were widely used as refrigerants and as propellants in aerosol cans. However, the release of chlorofluorocarbons into the atmosphere has been shown to be quite damaging to the earth s ozone layer. Since January 1978, the use of chlorofluorocarbons in aerosol cans in the United States has been banned, and efforts to develop both controls for existing chlorofluorocarbons and suitable replacements continue. The production and sale of freons have been banned in many countries. 

Although manufacture of CFCs was banned on December 31, 1995, the C—F and C—Cl bonds of CFCs are so strong that the molecules may remain in the atmosphere for 120 years. Within 5 years they diffuse into the upper stratosphere where ultraviolet photons can break the C—Cl bonds. This process releases chlorine atoms, as shovm here for Freon-12 ... 

A Freon leak in the air-conditioning system of an old car releases 25 g of CFjClj per month. What mass of chlorine does this car emit into the atmosphere each year ... 

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