The Earth's ozone layer protects all life from the sun's harmful radiation, but human activities have damaged this shield. Less protection from ultraviolet light will, over time, lead to higher skin cancer and cataract rates and crop damage. The ozone layer is one layer of the stratosphere, the second layer of the Earth’s atmosphere. The stratosphere is the mass of protective gases clinging to our planet. Ozone is only a trace gas in the atmosphere only about 3 molecules for every 10 million molecules of air. But it does a very important job. Like a sponge, the ozone layer absorbs bits of radiation hitting Earth from the sun. Even though we need some of the sun's radiation to live, too much of it can damage living things. The ozone layer acts as a shield for life on Earth. Ozone is good at trapping a type of radiation called ultraviolet radiation, or UV light, which can penetrate organisms’ protective layers, like skin, damaging DNA molecules in plants and animals. There are two major types of UV light: UVB and UVA. UVB is the cause of skin conditions like sunburns, and cancers like basal cell carcinoma and squamous cell carcinoma.
In the last thirty years, it has been discovered that stratospheric ozone is depleting as a result of anthropogenic pollutants. There are a number of chemical reactions that can deplete stratospheric ozone; however, some of the most significant depletion comes from the catalytic destruction of ozone by freed halogen radicals like chlorine and bromine. Overview of Ozone Depletion
Ozone depletion is term used to describe occurrences regarding the Earth's ozone layer. One of these observable trends is the slow and constant deterioration of the ozone in the atmosphere of about three percent per decade. The other is a great, though seasonal, reduction in the amount of ozone in the atmosphere over the polar regions, commonly described as an ozone hole. Although, the concentration of ozone in the stratosphere naturally increases and decreases with things like altitude, temperature, and weather, the considerable level of ozone reduction is not due to only natural factors (7). Synthetic chemicals and gases play a huge role in ozone depletion. Aerosols and chlorofluorocarbons, or CFCs, have been found to be largely responsible for the depletion of the ozone layer. The reduction of the ozone layer presents a large risk for many chemical and biological processes on the Earth's surface. Exposure to radiation that is usually shielded by the ozone layer has a variety of damaging effects on living organisms.
The Chapman Mechanism
In 1930, Sydney Chapman presented a sequence of reaction mechanisms to explain the formation, depletion, and maintenance of the ozone layer. The Chapman mechanism (or cycle) is made up of four reaction mechanisms. The first step in the creation of ozone occurs when short-wavelength UV light from the sun hits a molecule of oxygen gas. The light (or photon) has so much energy that it breaks the oxygen bond holding the atoms together, thus creating two oxygen atoms. Through this process, the oxygen essentially absorbs the short-wavelength UV light, but this still leaves a significant amount of UV light with longer wavelengths, which is where ozone comes in. In the second process, each of the two remaining oxygen atoms will then attach to two oxygen gas molecules, creating two separate ozone molecules. Short-wavelength UV light has enough energy to break apart ozone molecules (which are easier to separate than oxygen molecules). Thus, in the third part of the cycle, the ozone gas then breaks into one oxygen gas molecule and an oxygen atom, hence absorbing much of the remaining UV light. Otherwise, the O3 molecule can combine with another oxygen atom producing two molecules of oxygen gas, producing the forth step. These steps determine the overall amount of ozone in the stratosphere. However, Chapman’s cycle didn’t account for the destruction of...
References: 5.Ozone Science: The Facts Behind the Phaseout, 2010. United States Environmental Protection Agency.
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