Stratospheric ozone layer, photochemical

The Stratospheric Ozone Layer Its Photochemical Formation and Degradation... 

This report deals primarily with the origins and effects of ozone and other photochemical oxidants. It is limited, more or less, to the problem of urban pollution and to such closely related topics as natural background in the earth s boundary layer. No consideration is given to the stratospheric ozone layer and the effects produced by supersonic transport (sst) emission or halocarbons. 

The interest in the reaction still continues and has acquired special importance due to deleterious effect on stratospheric ozone layer of haloalkane free radicals generated by photochemical reactions in the atmosphere. 

Depletion of stratospheric ozone layer Global warming Formation of photochemical pollutants Acidification Pluman toxicity... 

O Classified as a volatile organic compound (VOC). VOC can react in the lower atmosphere to form ozone and other oxidants. VOC means any compound of carbon, excluding carbon monoxide, carbon dioxide, carbonic acid, metaUic carbides or carbonates, and ammonium carbonate, which participates in atmospheric photochemical reactions. Some compounds are specifically exempted firom this definition which is found in 40 C.F.R. 51.100(s). T Considered a hazardous air pollutant (HAP) and listed in Title III of the Clean Air Act Amendments of 1990. D A regulated stratospheric ozone layer depleter. 

Photochemical stability also can play an important role in solvent selection. Ethers are for instance easily attacked by UV light, to form in the presence of oxygen explosive peroxides a well-known industrial hazard. Fully halogenated solvents are on the other hand so stable, that, once evaporated, they remain a long time in the atmosphere without being degraded by sunlight. In this way they indirectly, finally affect the stratosphere ozone layer around the earth. 

Depletion of Stratospheric Ozone Layer from Photochemical Degradation... 

Another major feature of the vertical thermal structure of the atmosphere is due to the presence of ozone, O3, in the stratosphere. This layer is caused by photochemical reactions involving oxygen. The absorption of solar UV radiation by O3 causes the temperature in the stratosphere and mesosphere to be much higher than expected from an extension of the... 

Located several kilometres above the Earth s surface is the stratosphere. Here the ozone layer acts as a filter, protecting life on Earth from harmful low-wavelength ultraviolet radiation known as UV-C, which damages biological macromolecules such as proteins and DNA. In order to understand the effects of anthropogenic input into the stratosphere, the production and destruction of the ozone layer has been studied by a variety of photochemical models and experimental methods. 

In this section, we use another chain reaction to show the relation between the steady-state treatment and the quasi-equilibrium treatment. The former is more general than the latter, and leads to more complete but also more complicated results. Ozone, O3, is present in the stratosphere as the ozone layer, and in the troposphere as a pollutant. Ozone production and destruction in the atmosphere is primarily controlled by photochemical reactions, which are discussed in a later section. Ozone may also be thermally decomposed into oxygen, O, although... 

The ozone layer in the atmosphere is an important protective layer for life on the Earth. Ozone is photochemically produced from O2 in the atmosphere. The following account is from Pilling and Seakins (1995). First, oxygen atoms are generated by short-wavelength U V photolysis (at wavelengths below 242 nm) in the stratosphere. That is, UV photons split the oxygen molecule as follows ... 

The maximum concentration of ozone in the stratosphere (or the ozone layer) is about 9 ppm at an altitude of about 35 km. That is, the concentration of ozone in the so-called ozone layer is still very low. Transport of ozone in the atmosphere modifies ozone concentration levels at each altitude and latitude. It is emphasized that the steady-state concentration of O3 in the stratosphere is not the thermodynamic equilibrium concentration, but is established by kinetics of photochemical reactions. 

The stratosphere is often referred to as the ozone layer, because of the relatively high concentrations produced by photochemical reactions in this region of the atmosphere. Ozone, derived from the Greek word meaning to smell, was first discovered by Schonbein in 1839. It has a rather pungent smell, which is sometimes noticeable around copy machines and laser printers that use discharge processes. 

The main objective of the PAUR I project was to investigate how increased penetration of UV-B solar radiation through the atmosphere, resulting from stratospheric ozone depletion, affects photochemical production and chemical transformation of ozone and other photochemically active species in the lower atmospheric layers. 

CFC Abbreviation for chlorofluorocarbon, a type of organic compound in which some or all of the hydrogen atoms of an alkane have been replaced by fluorine and chlorine atoms. These substances are generally unreactive but they can diffuse into the stratosphere where they break down under the influence of ultraviolet light. The products of this photochemical process then react with ozone (in the ozone layer). Because of this, their use... 

Ozone is a gas that occurs naturally in relatively large concentrations in the upper-atmospheric layer known as the stratosphere. The stratosphere is between 5-10.6 mi (8-17 km) to about 31 mi (50 km) above the earth s surface. Stratospheric ozone is very important to life on the surface of Earth because it absorbs much of the incoming solar ultraviolet radiation, and thereby shields organisms from its deleterious effects. Since the mid-1980s, there has been evidence that concentrations of stratospheric ozone are diminishing as a result of complex photochemical reactions involving chloroflno-rocarbons (CFCs). These persistent chemicals are synthesized by humans and then emitted to the lower atmosphere, from where they eventually reach the stratosphere and deplete ozone. 

Because of their extreme stability against all kinds of aggressive chemical agent, for example radicals, perfluorocarbons and halofluorocarbons are not degraded in the lower layers of the atmosphere as are other pollutants. After several years, or even decades, they finally reach the stratosphere at altitudes of 20 to 40 km [26, 27]. In this layer, under the influence of short-wave UV irradiation, ozone is formed continuously (Scheme 1.2). This stratospheric ozone plays an essential role in preserving life on earth by absorbing the short-wavelength UV which would otherwise lead to an increase of photochemically induced mutations in most life-forms. For humans, over-exposure to short-wave UV irradiation results in a dramatically increased risk of skin cancer. Many crops and other plants also react rather sensitively towards an increase of UV exposure. 

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