11:32 am - Monday May 28, 2012

Ozone Layer

Ozone or trioxygen is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic O2. Ground-level ozone is an air pollutant with harmful effects on the respiratory systems of animals. Ozone in the upper atmosphere filters potentially damaging ultraviolet light from reaching the Earth’s surface. It is present in low concentrations throughout the Earth’s atmosphere. It has many industrial and consumer applications.

Ozone Layer in Atmosphere

ozone hole

The ozone layer is a layer in Earth’s atmosphere which contains relatively high concentrations of ozone (O3). This layer absorbs 93-99% of the sun’s high frequency ultraviolet light, which is potentially damaging to life on earth. Over 91% of the ozone in Earth’s atmosphere is present here. It is mainly located in the lower portion of the stratosphere from approximately 10 km to 50 km above Earth’s surface, though the thickness varies seasonally and geographically. The ozone layer was discovered in 1913 by the French physicists Charles Fabry and Henri Buisson. Its properties were explored in detail by the British meteorologist G. M. B. Dobson, who developed a simple spectrophotometer (the Dobsonmeter) that could be used to measure stratospheric ozone from the ground. Between 1928 and 1958 Dobson established a worldwide network of ozone monitoring stations which continues to operate today. The “Dobson unit”, a convenient measure of the total amount of ozone in a column overhead, is named in his honor.

Ozone Layer Depletion

Ozone depletion describes two distinct but related phenomena observed since the late 1970s: a steady decline of about 4% per decade in the total volume of ozone in Earth’s stratosphere (the ozone layer), and a much larger springtime decrease in stratospheric ozone over Earth’s polar regions. The latter phenomenon is referred to as the ozone hole. In addition to these well-known stratospheric phenomena, there are also springtime polar tropospheric ozone depletion events.

Ozone Layer Hole and Its Causes

The Antarctic ozone hole is an area of the Antarctic stratosphere in which the recent ozone levels have dropped to as low as 33% of their pre-1975 values. The ozone hole occurs during the Antarctic spring, from September to early December, as strong westerly winds start to circulate around the continent and create an atmospheric container. Within this polar vortex, over 50% of the lower stratospheric ozone is destroyed during the Antarctic spring.

As explained above, the primary cause of ozone depletion is the presence of chlorine-containing source gases (primarily CFCs and related halocarbons). In the presence of UV light, these gases dissociate, releasing chlorine atoms, which then go on to catalyze ozone destruction. The Cl-catalyzed ozone depletion can take place in the gas phase, but it is dramatically enhanced in the presence of polar stratospheric clouds (PSCs).

Destruction of Ozone Layer

There are many causes of ozone layer depletion, all of them manmade compounds that enter the atmosphere. They are chloroflurocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), methyl bromide, halons, methyl chloroform and carbon tetrachloride. Once they have been released into the atmosphere, they remain there for as long as 200 years.

Although there are numerous causes of ozone layer depletion, chloroflurocarbons have been identified as being the most damaging. These gases are used in many different industries in various ways. One example is the refrigerant gas used to run refrigeration and air-conditioning systems and heating, ventilation and air conditioning systems. Chloroflurocarbons are also used in firefighting equipment, aerosols, the production of installed foam and anesthetics.

Protection of Ozone Layer

The ozone layer is the main protector of Earth from excessively intensive ultraviolet (UV) radiation of the Sun. But unfortunately during the last 20 years the ozone layer over many world regions, including Latvia in fall and winter periods, was too ”thin”. As a result, the probability of skin cancer and eye cataracts increased, immunity weakened, agricultural crops and fishery catch decreased, etc. Results of some researches state that the ozone layer thinning has practically stopped at the present moment, while others state that the “ozone hole” is growing, i.e. in the year 2005 it was almost a record big size. Therefore one shall conclude that exactly this year and several following years will be determinant for ozone layer recovery.

Ozone layer protection is currently supported by 189 countries of the world, including Latvia. For almost all technologies applying ozone layer depletion matters there are replacement alternatives found, and production, trade, and application of theses matters is rapidly decreasing. For example, in the year 1986 the world consumed approximately 1 100 000 tons of HFO or CFC (one of the most widespread ozone layer depletion matters, also named Freon), but in 2001 the total amount of consumed HFO was only 110 000 tons.

Scientists forecast that in case of observation of currently implemented ozone layer protection measures the ozone layer will be recovered up to its normal condition by 2050 - 2060.

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