Ozone screen

All these photoreactions caused by uv light prevent H-bonding between base pairs which is fundamental to the replication and propagation of life (Figure 9.1). Some of these damages can be repaired, others are permanent and lethal to life. Therefore the importance of ozone screen in cutting off these deleterious radiations from the solar spectrum. 

Oscillator strength, 64, 65, 69, 81 Oxetane formation, 239, 255-256 Oxidation potential, 113 Ozone screen, 279, 280 Ozone, stratospheric, 345... 

We will look at the importance of the oxygen-ozone screen as a mechanism for protecting us from dangerous UV radiation in Chapter 7. 

The Chapman cycle is a series of chemical reactions related to the oxygen-ozone screening... 

Ozone, known for its beneficial role as a protective screen against ultraviolet radiation in the stratosphere, is a major pollutant at low altitudes (from 0 to 2000 m) affecting plants, animals and human beings. Ozone can be formed by a succession of photochemical reactions that preferentially involve hydrocarbons and nitrogen oxides emitted by the different combustion systems such as engines and furnaces. 

When writing a Lewis structure we restrict a molecule s electrons to certain well defined locations either linking two atoms by a covalent bond or as unshared electrons on a sm gle atom Sometimes more than one Lewis structure can be written for a molecule espe cially those that contain multiple bonds An example often cited m introductory chem istry courses is ozone (O3) Ozone occurs naturally m large quantities m the upper atmosphere where it screens the surface of the earth from much of the sun s ultraviolet rays Were it not for this ozone layer most forms of surface life on earth would be dam aged or even destroyed by the rays of the sun The following Lewis structure for ozone satisfies fhe ocfef rule all fhree oxygens have eighf elecfrons m fheir valence shell... 

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. 

H. Ozonizalion of organic compounds. The ozonization of each unsaturated organic compound is more or less an individual problem, but some general comments may be made. Organic ozonides are highly explosive, and hence it is safest to carry out the ozonization in a solvent which dissolves both the original compound and the ozonide. In all cases, a shatterproof screen of laminated safety glass should be placed between the operator and the tubes H, I, and J. A second screen should be placed back of the tubes to protect other pieces of the apparatus. 

OZONE LAYER A thin layer of ozone that lies about 25 kilometres above the earth in the stratosphere. Forms a protective screen against harmful radiation by filtering out ultra-violet rays from the sun. 

Gayberg, C. D. Screening tomatoes for ozone resistance. HortScience 6 3%-397, 1971. 

Physicochemical treatment of pharmaceutical wastewater includes screening, equalization, neutralization/pH adjustment, coagulation/flocculation, sedimentation, adsorption, and ozone and hydrogen peroxide treatment. Detailed descriptions of the various physicochemical treatment processes are described in the following sections. 

A 10-miUion-gallon-per-day wastewater treatment facility in El Paso, Texas, has operated since 1985. A PACT system operates as part of a treatment train that includes screening, the two-stage PACT system, lime treatment, two-stage recarbonization, sand filtration, ozonation, GAC filtration, chlorination, and finished water storage. Treatment costs for the entire system are 1.60 per 1000 gal (D19952E, p. 3). 

Above the troposphere is the stratosphere, which reaches a height of 50 kilometers. At an altitude of 20 to 30 kilometers in the stratosphere lies the ozone layer. Stratospheric ozone acts as a sunscreen, protecting Earths surface from harmful solar ultraviolet radiation. Stratospheric ozone also affects stratospheric temperatures. At the lowest altitudes, the temperature is coolest because of the solar screening effect of ozone air at this altitude is literally in the shade of ozone. At higher altitudes, less ozone is available for shading and temperature increases all the way to a warm 0°C at the top of the stratosphere. 

Most of the reactions the inorganic chemist encounters in the laboratory involve ionic species such as the reactants and products in the reactions just discussed or those of coordination compounds (Chapter 13). However, in the atmosphere there are many free radical reactions initiated by sunlight. One of the most important and controversial sets of atmospheric reactions at present is that concerning stratospheric ozone. The importance of ozone and the effect of ultraviolet (UV) radiation on life has been much discussed. Here we note briefly that only a small portion of the sun s spectrum reaches the surface of the earth and that parts of the UV portion that are largely screened can cause various ill effects to living systems. 

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