Earth atmospheric ozone

One of the chief uses of chloromethane is as a starting material from which sili cone polymers are made Dichloromethane is widely used as a paint stripper Trichloromethane was once used as an inhalation anesthetic but its toxicity caused it to be replaced by safer materials many years ago Tetrachloromethane is the starting mate rial for the preparation of several chlorofluorocarbons (CFCs) at one time widely used as refrigerant gases Most of the world s industrialized nations have agreed to phase out all uses of CFCs because these compounds have been implicated m atmospheric processes that degrade the Earth s ozone layer... 

Most chlorofluorocarbons are hydrolytically stable, CCI2F2 being considerably more stable than either CCl F or CHCI2F. Chlorofluoromethanes and ethanes disproportionate in the presence of aluminum chloride. For example, CCl F and CCI2F2 give CCIF and CCl CHCIF2 disproportionates to CHF and CHCl. The carbon—chlorine bond in most chlorofluorocarbons can be homolyticaHy cleaved under photolytic conditions (185—225 nm) to give chlorine radicals. This photochemical decomposition is the basis of the prediction that chlorofluorocarbons that reach the upper atmosphere deplete the earth s ozone shield. 

Depletion of the Ozone Layer. As a constituent of the atmosphere, ozone forms a protective screen by absorbing radiation of wavelengths between 200 and 300 nm, which can damage DNA and be harmful to life. Consequently, a decrease in the stratospheric ozone concentration results in an increase in the uv radiation reaching the earth s surfaces, thus adversely affecting the climate as well as plant and animal life. Pot example, the incidence of skin cancer is related to the amount of exposure to uv radiation. 

The wavelengths at which most of the components of a primitive Earth atmosphere absorb lie, with few exceptions, under 200 nm. The exceptions include ammonia (< 230 nm), hydrogen sulphide (<260 nm) and ozone (180-300 nm). However, ozone was probably present in the primeval atmosphere only in trace amounts, since free oxygen was only available in extremely low concentrations. The young Earth thus had no protective ozone layer, so short-wavelength UV irradiation could readily penetrate the atmosphere. 

UV-irradiated cells. Using cell-free cytosolic keratinocyte extracts, Simon and colleagues26 confirmed the role of membrane oxidation in NF-kB activation. Particularly important aspects of the experimental design employed by Simon and colleagues was the use of keratinocytes versus cells derived from a cervical cancer patient, and the use of biologically relevant UVB (290 to 320 nm) radiation versus UVC (200 to 290 nm) radiation, which is filtered out by the atmospheric ozone layer and does not reach the earth s surface. Overall, these data indicate that the activation of cytokine transcription, a step essential for the induction of immune suppression, can occur independently of UV-induced DNA damage and suggest that membrane lipid oxidation can serve as a UV photoreceptor. 

Halon - As employed in the fire protection industry, a gaseous fire suppression agent. Halon is an acronym for halogenated hydrocarbons, commonly bromotrifluoromethane (Halon 1301) and bromochlorodifluoro-methane (Halon 1211). Considered obsolete for fire protection purposes due to a possible environmental impact to the Earth s atmospheric ozone layer and beginning to be phased out or eliminated. 

Madronich, S Implications of Recent Total Atmospheric Ozone Measurements for Biologically Active Ultraviolet Radiation Reaching the Earth s Surface, Geophys. Res. Lett., 19, 37-40... 

Table 5. Atmospheric ozone increases from aircraft emission per NOx molecule emitted, relative to the increase in 1992. The emissions of NOx are die same as given in Table l.The values represent increases in global ozone concentrations from the Earth s surface to 16 km and is the average increase for the models that participated in the model studies given in Table 4.

High up in the atmosphere, around 20 km from the surface of the earth, the ozone layer acts as a shield and protects the earth from the harmful UV rays present in the incoming solar radiation. But for this layer, all life on earth would have been scorched. Ozone is used to sterilize drinking water and to remove bad odours and tastes. 

Tal rose [23] and many other authors [24, 25] presented an interesting sphere of HO radical participation non-linear reactions and ozonosphere processes proceeding at ozone formation in the Earth atmosphere and chemical lasers. 

Another important mutagen is ultraviolet light. Recent concern about the depletion of the atmospheric ozone layer by chlorofluorocarbon compounds (CFCs) is due to the role of the ozone in absorbing UV radiation before it can cause mutations in the organisms at the earth s surface. All the DNA bases efficiently absorb UV and become chemically reactive as a result. The formation of pyrimidine dimers from adjacent thymidine residues in DNA interferes with replication and transcription of DNA. See Figure 8-14. 

Another example is that of chlorofluorocarbons (CFC). All chlorofluorocarbons show absorption in the range 160-280 nm. This UV radiation is available near ozone layer of earth atmosphere. Light spectrum available on the surface of earth is perfectly transparent to chlorofluorocarbons and thus behaves as photochemically inert. These do not dissolve in water and thus are not removed by rain. Slowly these molecules rise and reach the ozone layer. Their photons of 160-280 nm are available absorption of which lead to primary photochemical reaction... 

Ozone exists naturally in the upper atmosphere of the earth. The ozone layer is especially important because it absorbs ultraviolet light and thus acts as a screen to prevent this radiation, which can cause skin cancer, from penetrating to the earth s surface. When an ozone molecule absorbs this energy, it splits into an oxygen molecule and an oxygen atom ... 

The concerns for changes in atmospheric ozone can be divided into two major categories changes in total column of ozone, and changes in the concentrations at particular altitudes. The penetration of ultraviolet radiation to the surface of the earth is determined almost entirely by the total amount of ozone in the atmospheric column, with very litde dependence on the altitude distribution of this ozone. However, if the prime concern is with processes such as the conversion of ultraviolet energy into heat after absorption by ozone (i.e. with the temperature structure of the stratosphere), then a redistribution of ozone to different altitudes is extremely important. 

Ozone absorbs ultraviolet radiation below 320 nm. It thus forms an indispensable shield in the upper atmosphere, protecting the Earth s surface from most of the potentially hazardous effects of such high-energy electromagnetic radiation. There is now increasing concern because atmospheric pollutants are depleting the ozone layer worldwide, with the most serious depletion over Antarctica as a result of seasonal variations in high-altitude air circulation. In the upper atmosphere, ozone is formed from O2 ... 

The reason for this ban is the damage caused by CFCs to Earth s ozone layer. Ozone (O3) is a form of oxygen that filters out harmful radiation from the sun. When CFCs escape into the atmosphere, they attack and destroy ozone molecules. They reduce the protection against radiation provided by ozone. 

Figure 3. Record of concentration of atmospheric ozone at the earth s surface for...

AAan s interest in atmospheric ozone began more than 100 years ago when C. F. Schonbein, who was responsible for its discovery, claimed its presence in the normal earth s atmosphere (S4). Schonbein s ozonometer consisted of paper soaked in potassium iodide and starch for years data thus obtained were subject to the criticism that the chemical reaction used was not specific to ozone. 

You are probably aware of some of the damaging effects of ultraviolet radiation from the Sun if you have ever suffered from a sunburn. Overexposure to ultraviolet radiation also is harmful to plants and animals, lowering crop yields and disrupting food chains. Living things can exist on Earth because ozone, a chemical in Earth s atmosphere, absorbs most of this radiation before it reaches Earth s surface. A chemical is any substance that has a definite composition. Ozone is a substance that consists of three particles of oxygen. 

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. 

The carbon-chlorine bond in most chlorofluorocarbons can be homolytically cleaved under photolytic conditions (185-225 nm) to give chlorine radicals. This photochemical decomposition is the basis of the prediction that chlorofluorocarbons that reach the upper atmosphere deplete the earth s ozone shield. 

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