Shielding ultraviolet radiation

A representation of the stratospheric system that shields terrestrial life from excessive solar ultraviolet radiation is presented in Figure 4. Our primary concern is the decrease of stratospheric ozone, most striking in the Antarctic, which has been linked to increases in CFCs from the troposphere, and the possible increased transport of these compounds between the stratosphere and the troposphere by increased temperature driven circulation. 

The collagen shield, fabricated from procine scleral tissue, is a spherical contact lens-shaped film whose thickness can be made to vary from 0.027 to 0,071 mm. It has a diameter of 14.5 mm and a base curve of 9 mm. Once the shield is hydrated by tear fluid and begins to dissolve, it softens and conforms to the corneal surface. Dissolution rates can be varied from 2 to as long as 72 hr by exposing the shields to ultraviolet radiation in order to achieve varying degrees of crosslinking. 

Thus harmful ultraviolet radiation is transformed by ozone into a not-so-harmful slight heating of the stratosphere. Note that ozone is not lost in this transformation, which means it can continue to shield Earths surface indefinitely from ultraviolet radiation. 

The oxygen atom produced in this step can react with oxygen molecules to produce more ozone, so normally the ozone concentration in the stratosphere remains constant, with seasonal variations. Because the decomposition of ozone absorbs ultraviolet radiation, it helps to shield the Earth from radiation damage. 

Relatively little of the atmosphere s mass is located above the troposphere, but the chemistry that occurs there is nonetheless crucial to maintaining life on earth. Particularly important is what takes place in the ozone layer, an atmospheric band stretching from about 20-40 km above the earth s surface. Ozone (03) is a severe pollutant at low altitudes but is critically important in the upper atmosphere because it absorbs intense ultraviolet radiation from the sun. Even though it is present in very small amounts in the stratosphere, ozone acts as a shield to prevent high-energy solar radiation from reaching the earth s surface, where it can cause such problems as eye cataracts and skin cancer. 

Chlorofluorocarbons (CFCs) are widely used in refrigeration and air conditioning, insulation, and plastic foams. Although nontoxic and nonflammable, they are believed to deplete the ozone layer in the atmosphere which shields the earth from the sun s ultraviolet radiation. While action to control the production and use of CFCs was still being debated, McDonalds s Corporation announced it would no longer use foam food containers produced with the aid of CFC in its fast food outlets. 

Ozone A molecule made up of three atoms of oxygen. It occurs naturally in the stratosphere and provides a protective layer shielding the Earth from harmful ultraviolet radiation. In the troposphere, it is a chemical oxidant, a greenhouse gas and a major component of photochemical smog. 

Rawlings, T. A., Shields against ultraviolet radiation an additional protective role for the egg capsules of benthic marine gastropods, Mar. Ecol. Prog. Ser., 136, 81, 1996. 

Bob tosses an iron cup to Mr. Plex who catches it in his mouth (figure 2.2). Next, Bob grabs a blowtorch and walks to Mr. Plex. Don t worry. Your diamond body should shield you from the effects of the flame. Now watch. As I heat the cup, it first glows red, then yellow, and finally white. When it s white-hot, it also emits ultraviolet radiation that we can t see, but Mr. Plex can see it with his alien eyes. ... 

Ozone, produced in the stratosphere by the action of ultraviolet light on 02, helps shield the surface of the earth from harmful ultraviolet radiation. Ozone is slowly decomposed by reaction with oxygen atoms according to the following equation ... 

Since the atmosphere shields us from most deep ultraviolet radiation and from infrared radiation, the bulk of visible light (the solar spectrum) ranges from 350 to 750 nm. The 25,000 Frauenhofer15 "dark" lines are interruptions (in the range 295 to 1000 nm) in the continuous solar emission spectrum, due to absorption by the chemical elements present in the sun s atmosphere. Ultraviolet radiation was discovered by Ritter16 in 1801. Some radio waves do penetrate the earth s atmosphere, and they are most intense during solar storms. Infrared radiation also penetrates to some extent. 

Prebiological levels of O3 offered no shielding of the surface to incoming solar ultraviolet radiation (200-300 nm). 

Ozone is vital to life it acts like a shield, protecting the earth s surface from destructive ultraviolet radiation. A decrease in ozone concentration in this protective layer would have some immediate consequences, including an increase in the incidence of skin cancer and eye cataracts. Other long-term effects include a reduced immune response, interference with photosynthesis in plants, and harmful effects on the growth of plankton, the mainstay of the ocean food chain. 

The reactor must he properly screened. Wear special protective goggles, or better still a face shield which offers protection against ultraviolet radiation if the apparatus is to be adjusted (or samples taken) while the lamp is on. When doing this also protect the hands with gloves and make sure that no other areas of skin would be exposed to radiation in... 

Approximately 90% of the ozone in the atmosphere is found in the stratosphere (15-50 km), with only —10% in the troposphere (0-15 km). Stratospheric ozone is very important because it absorbs ultraviolet radiation (200-300 nm) from the Sun and shields the surface from this biologically lethal radiation. Stratospheric ozone is destroyed via a series of chemical reactions involving NO, OH, Cl, and Br. These species destroy stratospheric ozone through the following catalytic cycle where X may be any of the following NO, OH, Cl, or Br (Wayne, 1991)... 

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 ... 

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. 

Ozone layer The layer of ozone that shields Earth from harmful ultraviolet radiation from the sun. 

By the mid-1980s, however, evidence showed that the compounds were damaging Earth s ozone layer. This layer lies at an altitude of 12 to 30 miles (20 to 50 kilometers) above Earth s surface. It is important to life because it shields Earth from the sun s harmful ultraviolet radiation. As a result, CFCs were phased out. The compounds are no longer produced... 

Above the troposphere, temperatures increase with altitude, reaching a maximum of nearly 2°C at about 50 km. This region of the atmosphere is called the stratosphere. The stratosphere contains a layer of ozone, a gas that helps shield Earth s surface from the Sun s harmful ultraviolet radiation. Ozone protects Earth by absorbing solar radiation, which raises the temperature of the stratosphere in the process. You read about the ozone layer in Chapter 1 as you began your study of chemistry. 

In addition to light gases, the upper atmosphere—more specifically, the stratosphere—contains a substance called ozone. In Chapter 1, you learned about the ozone layer and how it contributes to shielding Earth s surface from ultraviolet radiation. Now let s examine the chemical reactions that lead to the formation of ozone in the stratosphere. 

Stratospheric ozone is produced at maximum rates in equatorial regions, where solar radiation is most intense. Ozone does not really occur as a layer, but instead as a broadly distributed gas whose peak concentration occurs in midstratosphere. The total amount of ozone present in the atmosphere is small, typically between 200 and 400 Dobson units. A Dobson unit is the amount of ozone that, if gathered together in a thin layer covering Earth s surface at a pressure of 1 atm, would occupy a thickness of 1/100 of a millimeter (10 gm). The entire ozone shield, which protects life on Earth from damage by the UV-B radiation of the Sun (ultraviolet radiation in the 280-320 nm range), is equivalent to a layer of ozone only 2 to 4 mm thick at sea level pressure. 

Oxygen can also cycle between the biosphere and the lithosphere — when marine organisms with calcium carbonate (CaC03) shells die, the shells are buried on the shallow waters of the sea floor, becoming the limestone of the lithosphere. A small amount of atmospheric oxygen is transformed to ozone, O3, and the ozone layer in the stratosphere plays an important role in shielding our planet from harmful ultraviolet radiation. 

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