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Causes and Effects Ozone Depletion (in our Stratosphere) - the Greenhouse Effect and UVC-rays - Swiss Chemistry Vormatur
[EDITOR'S NOTE: In June 2012 I will have taken my finals in chemistry. In Switzerland, it is called the "Vormatur" and I hope I can share my knowledge with other students! Other exam topics are: Macromolecules and Polymers, Acid/Base reactions, Redox reactions, environmental chemistry (ozone depletion), Molecules/Salts/Metals/Atomic lattice, Equilibrium equations and organic chemistry]
Ozone in the Stratosphere and chemical reactions
Ozone is an important constituent of the stratosphere. Ozone is a molecule with the formula: O3.
Ozone occurs in 15 km to 50 km in height (stratosphere). About 90% of the total ozone is in the stratosphere, where it fulfils a very important function for the earth, but also for the humans and animals. The other 10% are in the troposphere, what can be a threat to people and animals.
Ozone absorbs most of the UVC rays. With the absorption of the UV-rays, Ozone molecules become excited and decay into oxygen and into atomic oxygen:
O3 → O2 + O
Of course, this process is spontaneously reversible:
O2 + O → O3
This is due to the UV-rays which carry a lot of energy (only those with a short wave-length) and can excite O2.
(Basic equation: 2O3 → 3O2)
There is also another possible reaction for the creation of ozone. In presence of tropospheric Nitrogen dioxide the following reaction can occur (with the energy of UV-rays):
NO2 + O2 → NO + O3
The same can also happen during thunderstorms, where enormous amounts of energy are released and thus enables the break up the strong bonds of nitrogen dioxide.
Although Ozone has a half-life time of 30 minutes it is nothing new that the concentration of ozone fluctuates.
But with the introduction of all the industries, mankind started to produce so-called anthropogenic molecules: chlorofluorocarbon, CFCs, molecules. Those are extremely reactive radicals in the stratosphere and therefore initiate the reaction with O3 very easily as O3 is already a very strong acid. This leads to a drastic decrease of Ozone and the well-known “Ozone depletion” occurred.
Those molecules, for example, Cl2 lose their double bonds in higher altitudes due to the UV-rays. Therefore, 2Cl• are formed, which are very reactive radicals. In presence of ozone, the following reaction occurs:
Cl• + O3 → ClO + O2
ClO can react with ozone a second time, destroying the ozone layer even more.
ClO + O3 → Cl• + 2O2
This is also the case with other halogens like bromide etc.
With such a low amount of ozone the dangerous UV-rays are much more likely to reach the ground and heat up the earth. But not only does this mean an increase in temperature, but also the risk of cancer and other health and environmental issues increase drastically.
Seasonally conditioned fluctuations
During the year, the concentration of ozone changes due to the total sunlight hours of a day.
During the winter months, where the sun shines less and a day is shorter, the concentration of ozone is usually higher. That is due to less UV-rays being absorbed by ozone and therefore, less catalyzing energy can induce a reaction.
During the summer months, a day becomes longer and the sun rays are more intense. This leads to a lot of absorptions by the ozone molecules and a reaction is a lot more often catalyzed.
Problems of ozone in the troposphere
The above stated events all happen in the stratosphere. 10% of ozone is in the troposphere, where it also carries out important duties.
Ozone is extremely reactive. Even more reactive than O-! The advantage is that ozone is greenhouse gas and reacts with methane (CH4) and other hydrocarbons. But it also reacts too easily with CFCs which can form a toxic gas. The new formed molecules descend to the earth and can cause health problems!
Development of greenhouse effect
There is a natural way of the greenhouse effect and a man-made way.
Clouds are able to reflect the infrared radiation back to the earth and therefore, keep the earth warm. Also, water molecules in the atomsphere and CO2 are able to absorb infrared radiation. These two very important molecules absorb nearly the whole infrared spectra (warmth or heat) and are also responsible to keep the temperature of our earth at a reasonable level.
The man-made or industrial version of this would be all the exhaust gases which are emitted by the humans. CFCs, CO2 emission, ozone and hydrocarbons are capable of storing the energy respectively of reflecting the rays back to the earth. This is also known as global warming.
Consequences and effect of greenhouse effect
Effects and consequences:
There is a whole chain of extremely fatal effects of global warming. The North and South poles melt faster and therefore the molten ice increases the sea level by 5 to 7 centimeters! This causes the extinction of many animals, because they are forced to emigrate and adapt to a completely new environment, what is very hard for them and can cause death to many species. Also, extreme periods of floods and droughts could occur, the position of streams will be shifted and even the climate zones will be shifted (up to 100 km!).