ozone layer depletion and effects essay
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Here is your essay on ozone layer depletion!
Ozone (O3) is a triatomic form of oxygen. It is found largely in the stratosphere that extends from about 6 km at the poles and 17 km at the equator to about 50 km above the earth’s surface. It is present in traces less than 1 ppm) in the atmosphere. It has a peak concentration (10 mg kg-1) in the stratosphere.
Ozone has been the most reactive form of molecular oxygen and the fourth most powerful oxidizing agent. It has a pleasant concentration at about 2 ppm or less, but higher concentration is irritating. It is used as a disinfectant and bleaching agent.
In nature O3 is formed in the stratosphere when ultraviolet light strikes an oxygen molecule. A photon splits the oxygen molecule into two highly reactive oxygen atoms (O). These combine quickly with an oxygen molecule to form ozone. The O3 readily absorbs UV light and dissociates into its constituent components.
Being a natural constituent of the stratosphere, O3 is regularly formed and destroyed in a cyclic manner with solar radiation as the driving force. In the absence of any other disturbances, O3 settles into a dynamic steady state in which the rate of its formation is equal to the rate of its destruction.
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Stratospheric ozone is formed through a continuous complex process of photochemical reaction involving the splitting of oxygen molecules into two oxygen atoms by solar energy and each atom further combines with oxygen molecules to produce ozone. Because the process is sunlight dependent, more ozone is produced at lower latitudes due the concentration of high solar radiation around the equator; as such ozone is continually produced and destroyed in these complex chemical reactions. The global distribution of ozone depends on conditions such as the availability of bromine and chlorine in the atmosphere, high solar intensity and latitudinal location that favour the production of the molecules.
Without this layer, UV-B radiation when reaching the earth is capable of damaging plant and animal tissues, increasing the risk of health problems such as skin cancer in humans as well as destroying both terrestrial and aquatic ecosystems.
Depletion of the ozone has been observed over the years due to the release of chemical substances into the atmosphere by humans. In 2005, scientists have observed the increase in ozone depleting substances (ODS) which results to the thinning of this protective layer over Arctic and Antarctic poles by about 30 – 50%, and a global average reduction of about 3 – 6% compared to the pre – 1980 levels. The process of depletion begins with the release of the ozone depleting substances (ODS) such as chlorine and bromine and chlorofluorocarbons (CFCs) mostly from human sources. These gases further accumulate into the atmosphere for some time depending of their resident times and then transported to the stratosphere through vertical mixing. These non-reactive gases are further converted into reactive compounds by UV radiation, then chemical reactions takes place to destroy the ozone layer. Finally, these gases are transported back to the troposphere where they are removed through precipitation.
Climate change and ozone layer depletion are interlinked because ozone itself is a greenhouse gas and together with other ozone depleting substances such as bromine (Br) and chlorine (Cl) contribute to global warming. Therefore any changes in the atmospheric concentration and distribution of ozone will have significant impact on the global climate system.
Release of these (ODS) substances including carbon dioxide and chlorofluorocarbons has a cooling effect on the stratosphere. This cooling effect favours the chemical reactions in chlorine and bromine thereby contributing to the formation of Polar Stratospheric Clouds (PSC), a condition that results in the depletion of ozone.
Studies have proved that the decrease in stratospheric ozone observed over Antarctica led to changes in the interactions between the stratosphere and the earth. These changes alter the atmospheric circulation particularly the North Atlantic oscillation (NAO), which in turn has an effect on variation of climate around the Atlantic.
Depletion of the ozone has another significant effect on the global biogeochemical cycles which has profound effect on the climate system. Increase in the amount UV-B modifies the carbon cycle by affecting the uptake of CO2 by plants during photosynthesis, as well as carbon storage in plants tissues as biomass.
Because the terrestrial ecosystem serves as a net sink for carbon, changes in the amount of UV radiation is capable of disturbing the photosynthetic and respiration processes which link the atmospheric carbon and terrestrial carbon uptake and release. Within the terrestrial ecosystems, certain plant species become more susceptible to increased UV radiation, hence reducing their ability to capture and store atmospheric carbon dioxide.
Furthermore, a change in the UV radiation increases the rate of productivity of soil micro organisms such as fungi thereby increasing the rate of carbon release from biomass decomposition. This accelerated turn over time of carbon through this process of photo degradation or photo transformation decreases the storage capacity of the soil as a major carbon sink, as such contributing to global warming. Scientific projections from models suggest a major shift in global ecosystems from cooler and wetter to warmer and drier conditions in response to climate change-UV interaction.