Introduction to Ozone Layer
The ozone layer is basically naturally occurring gas in the region of stratosphere where ozone particles are accumulated. Ozone layer is also naturally broken down but there is a balance between its formation and natural depletion.
As a result the total amount of ozone remains constant. But ozone layer thickness varies with altitude and seasonal change. Ozone concentration is highest between 19 – 23 km.
Most of ozone is formed at equator where there is maximum sunshine but with winds it travels at high altitude and get accumulated in stratosphere.
The ozone layer is a layer in Earth’s atmosphere which contains relatively high concentrations of ozone (O3).
Introduction to Ozone Layer
Ozone (O3) is a colourless gas just like oxygen (O2) but it has very harsh odour. It is very rare as compared to oxygen. It is estimated that out of 10 million air molecules about 2 millions are of O2 and only 3 are of ozone. The process of ozone formation is called as photolysis.
When the UV radiations from sun strike the O2 molecules, it causes splitting of O2. Oxygen molecules react with oxygen atoms in the upper atmosphere to form ozone. Stratospheric ozone is measured from the ground in units called Dobson Unit (D.U). Normal ozone concentration is between 300 – 350 D.U.
The ozone layer is basically naturally occurring gas in the region of stratosphere where ozone particles are accumulated.
Ozone layer is also naturally broken down but there is a balance between its formation and natural depletion.
As a result the total amount of ozone remains constant. But ozone layer thickness varies with altitude and seasonal change. Ozone concentration is highest between 19-23 km.
Most of ozone is formed at equator where there is maximum sunshine but with winds it travels at high altitude and get accumulated in stratosphere.
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.
Over91% 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, 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 Dobson meter) 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
Health Risk Associate with Ozone Layer
Overexposure to UV radiation has a range of serious health effects, including skin cancers (contributing to an increase in melanoma), eye damage (including cataracts) and immune system suppression:
1. Eye Diseases
UV radiation also damages the eye‘s outer tissues causing snow blindness‖, the ocular equivalent of sunburn.
UVB‘s role in cataract formation is complex but some subtypes appear to be associated with UV exposure. As a result, uncontrolled ozone depletion was projected to cause significant increases in cataracts.
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2. Immune Suppression
UV exposure causes both local and whole-body immune suppression. Increased UV induced immune suppression due to uncontrolled ozone depletion could have influenced patterns of infectious disease, and the effectiveness of vaccination, but might also have decreased the occurrence of various autoimmune diseases.
3. Skin Cancer
UV radiation is a cause of skin cancer (melanoma and other types) in fair-skinned humans.
Increases in UV radiation due to uncontrolled stratospheric ozone depletion would have led to more severe sunburn and large increases in skin cancer incidence (subject to changes in individual behaviour).
4. Ozone Layer Depletion
Ozone depletion describes two distinct, but related observations: a slow, steady decline of about 4 percent per decade in the total volume of ozone in Earth’s stratosphere (ozone layer) since the late 1970s, and a much larger, but seasonal, decrease in stratospheric ozone over Earth’s Polar Regions during the same period.
The latter phenomenon is commonly referred to as the ozone hole. In addition to this well-known stratospheric ozone depletion, there are also tropospheric ozone depletion events, which occur near the surface in Polar Regions during spring.
The most pronounced decrease in ozone has been in the lower stratosphere. However, the ozone hole is most usually measured not in terms of ozone concentrations at these levels (which are typically of a few parts per million) but by reduction in the total column ozone, above a point on the Earth’s surface, which is normally expressed in Dobson units, abbreviated as “DU”.
Marked decreases in column ozone in the Antarctic spring and early summer compared to the early 1970s and before have been observed using instruments such as the Total Ozone Mapping Spectrometer (TOMS).
Reductions of up to 70% in the ozone column observed in the austral (southern hemispheric) spring over Antarctica and first reported in 1985 (Farman et al 1985) are continuing.
Through the 1990s, total column ozone in September and October have continued to be 40–50% lower than pre-ozone-hole values. In the Arctic the amount lost is more variable year-to-year than in the Antarctic. The greatest declines, up to 30%, are in the winter and spring, when the stratosphere is colder.
5. Ozone Depletion Process
Ozone depletion process in the stratosphere leads to increase of UV-B on the ground with its harmful effects on health, ecosystems, aquatic system, materials etc. it is estimated that about 3 – 5.5% O3 depleted in the northern hemisphere during 1969 – 1988.
In general there are three principal ways of O3 depletion:
Hydrogen System (OH System)
Nitrogen System (N2O)
Chlorine System (CFCL3 or CF2CL2)
The OH system depletes only 10% of O3.
OH can also be formed from oxidation of CH4(CH4+O(ID) – CH3+OH). OH then reacts as above.
Sixty percent of ozone depletion occurs through N2O system. N2O is produced by bacterial action of microorganisms in ocean and soil (denitrification) diffuse upwards from troposphere to stratosphere where it react with O in the presence of light to produce NO which then deplete O3.
Neutral chlorine contributes only to very little to O3 destruction. But CFCL3, CFCL2 are the principal O3 destroyers.
In summary, most of ozone is formed at equator where there is maximum sunshine but with winds it travels at high altitude and get accumulated in stratosphere.
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.
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
The ozone layer is basically naturally occurring gas in the region of stratosphere where ozone particles are accumulated. Ozone layer is also naturally broken down but there is a balance between its formation and natural depletion.
As a result the total amount of ozone remains constant. Depletion of the ozone layer has some negative impact on health of humans.
Ozone depletion describes two distinct, but related observations: a slow, steady decline of about 4 percent per decade in the total volume of ozone in Earth’s stratosphere (ozone layer) since the late 1970s, and a much larger, but seasonal, decrease in stratospheric ozone over Earth’s Polar Regions during the same period.
The latter phenomenon is commonly referred to as the ozone hole. In addition to this well-known stratospheric ozone depletion, there are also tropospheric ozone depletion events, which occur near the surface in Polar Regions during spring.
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