Chlorofluorocarbon - Wikipedia
CVBr LOADING AND SCENARIOS FOR CFC SUBSTITUTES. .. in atmospheric ozone or the linearity of their relationship to chlorine/bromine loading .. emissions based on U.S. EPA analysis as described in the test, and are consistent. ozone layer and discuss how it influences the UV-radiation reaching the ground. .. relationship between ozone and the greenhouse effect will not be discussed in this related to the decreased release of CFC's and other ozone destructing . Chlorofluorocarbons (CFCs) are heavier than air, so how do scientists suppose that these chemicals reach the altitude of the ozone layer to adversely affect it?.
The atmosphere is not stagnant. Winds mix the atmosphere to altitudes far above the top of the stratosphere much faster than molecules can settle according to their weight. Gases such as CFCs that are insoluble in water and relatively unreactive in the lower atmosphere below about 10 kilometers are quickly mixed and therefore reach the stratosphere regardless of their weight. Much can be learned about the atmospheric fate of compounds from the measured changes in concentration versus altitude.
For example, the two gases carbon tetrafluoride CF4, produced mainly as a by-product of the manufacture of aluminum and CFC CCl3F, used in a variety of human activities are both much heavier than air.
Carbon tetrafluoride is completely unreactive in the lower There have also been measurements over the past two decades of several other completely unreactive gases, one lighter than air neon and some heavier than air argon, kryptonwhich show that they also mix upward uniformly through the stratosphere regardless of their weight, just as observed with carbon tetrafluoride. CFC is unreactive in the lower atmosphere below about 15 kilometers and is similarly uniformly mixed there, as shown.
The abundance of CFC decreases as the gas reaches higher altitudes, where it is broken down by high energy solar ultraviolet radiation. The net reaction in both cases is two ozone molecules forming three oxygen molecules.
Ozone destruction Cycles 2 and 3 are catalytic, as illustrated for Cycle 1, because chlorine and bromine gases react and are reformed in each cycle.
Global warming caused by chlorofluorocarbons, not carbon dioxide, new study says
Sunlight is required to complete each cycle and to help form and maintain ClO abundances. The very thing that makes Ozone good for filtering UV radiation makes it easily destroyed: Antarctic Ozone Hole As winter arrives, a vortex of winds develops around the pole and isolates the polar stratosphere.
Chemical reactions on the surfaces of ice crystals in the clouds release active forms of CFCs. Natural events such as Volcanic Eruptions can strongly influence the amount of Ozone in the atmosphere.Stratospheric Ozone
However, man-made chemicals such as CFCs or chlorofluorocarbons are now known to have a very dramatic influence on Ozone levels too. CFCs a were once widely used in aerosol propellants, refrigerants, foams, and industrial processes. Emission, accumulation, and transport. The halogen source gases, often referred to as ozone-depleting substances ODSsinclude manufactured chemicals released to the atmosphere in a variety of applications, such as refrigeration, air conditioning, and foam blowing.
Chlorofluorocarbons CFCs are an important example of chlorine-containing gases. Emitted source gases accumulate in the lower atmosphere troposphere and are transported to the stratosphere by natural air motions. The accumulation occurs because most source gases are highly unreactive in the lower atmosphere. Small amounts of these gases dissolve in ocean waters.
- Global warming caused by chlorofluorocarbons, not carbon dioxide, new study says
The low reactivity of these manufactured halogenated gases is one property that makes them well suited for specialized applications such as refrigeration. Some halogen gases are emitted in substantial quantities from natural sources. These emissions also accumulate in the troposphere, are transported to the stratosphere, and participate in ozone destruction reactions. These naturally emitted gases are part of the natural balance of ozone production and destruction that predates the large release of manufactured halogenated gases.
Conversion, reaction, and removal.
Halogen source gases do not react directly with ozone. In a self-funded research expedition ending inLovelock went on to measure CFC in both the Arctic and Antarctic, finding the presence of the gas in each of 50 air samples collected, and concluding that CFCs are not hazardous to the environment.
The experiment did however provide the first useful data on the presence of CFCs in the atmosphere.
The damage caused by CFCs was discovered by Sherry Rowland and Mario Molina who, after hearing a lecture on the subject of Lovelock's work, embarked on research resulting in the first publication suggesting the connection in It turns out that one of CFCs' most attractive features—their low reactivity— is key to their most destructive effects.
CFCs' lack of reactivity gives them a lifespan that can exceed years, giving them time to diffuse into the upper stratosphere.
Advances in Meteorology
This was later superseded by broader regulation by the EPA under the Clean Air Act to address stratospheric ozone depletion . NASA projection of stratospheric ozone, in Dobson unitsif chlorofluorocarbons had not been banned. Byin response to a dramatic seasonal depletion of the ozone layer over Antarcticadiplomats in Montreal forged a treaty, the Montreal Protocolwhich called for drastic reductions in the production of CFCs.
Indiplomats met in London and voted to significantly strengthen the Montreal Protocol by calling for a complete elimination of CFCs by the year By the yearCFCs should have been completely eliminated from developing countries as well. Ozone-depleting gas trends Because the only CFCs available to countries adhering to the treaty is from recycling, their prices have increased considerably.
A worldwide end to production should also terminate the smuggling of this material. The report estimated between 7, and 14, tonnes of CFCs are smuggled annually into developing countries. The cost of replacing the equipment of these items is sometimes cheaper than outfitting them with a more ozone-friendly appliance.
Additionally, CFC smuggling is not considered a significant issue, so the perceived penalties for smuggling are low. In public attention was drawn to the issue, that at an unknown place in east Asia an estimated amount of By the time of the Montreal Protocolit was realised that deliberate and accidental discharges during system tests and maintenance accounted for substantially larger volumes than emergency discharges, and consequently halons were brought into the treaty, albeit with many exceptions.
Regulatory gap[ edit ] While the production and consumption of CFCs are regulated under the Montreal Protocol, emissions from existing banks of CFCs are not regulated under the agreement.