The ozone layer is located in a layer of the Earth´s atmosphere known as the stratosphere. The ozone layer protects the Earth from the ultraviolet (UV) radiation from the sun. Ozone gas is created naturally in the stratosphere by the combination of molecular oxygen (O2) and atomic oxygen (O). While ozone is found throughout the entire Earth´s atmosphere, it is most concentrated in a region of the stratosphere 15-30 km (9-19 miles) above the Earth´s surface. The ozone layer protects all forms of life on Earth from the sun´s harmful UV radiation. Human activities are known to contribute to the depletion of the ozone layer.
Where is the ozone layer?
The Earth´s atmosphere consists of various layers. The troposphere, which is the lowest layer, comprises the first 10 km (6.2 miles). The stratosphere extends from 10 km (6.2 miles) to about 50 km (31 miles) of altitude. In the stratosphere, there is a temperature inversion, where the air temperature rises with increasing altitude. The temperature inversion is due to the absorption of UV radiation by ozone gas. The concentration of ozone is higher at altitudes of 25 km (16 miles), where the concentration of ozone is of 2 ozone molecules for every million air molecules. The ozone layer absorbs the portion of UV light called UVB, which is related to very harmful effects to humans, crops and animals.
How the ozone layer is created
Ozone molecules are permanently formed and destroyed in a cycle known as the ozone-oxygen cycle. Ozone molecules are created when UV light hits oxygen molecules (O2) and splits them into atomic oxygen (O). Oxygen atoms then combine with molecular oxygen to form ozone (O3). When formed, an ozone molecule remains unstable, and when it is hit by UV radiation, it can be broken down into molecular and atomic oxygen in an ongoing process known as the ozone-oxygen cycle. The concentration of ozone is denser in between 20-40 km (12-24 miles) in the Earth´s stratosphere, where the concentrations may reach 2-12 parts per million.
Ozone depletion
For over 50 years, chlorofluorocarbons (CFCs) were widely used until the 1970´s when their use was prohibited. CFCs are safe in the troposphere, where they rarely combine with other substances; however, when they enter the stratosphere, they´re broken down by UV radiation, releasing atomic chlorine and bromine, which are known to rapidly damaging the ozone layer. In the present, hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) are being used as substitutes for CFCs, as they contain a reduced amount of chlorine atoms than CFCs, causing less damage to the ozone layer; nevertheless, these gases are greenhouse gases, contributing to the warming of the planet.
Ozone concentrations
The density of the ozone layer fluctuates geographically and seasonally. The ozone layer is less dense at the tropical latitudes and denser at the poles. It is also thicker in spring and thinner in autumn in the North Pole. Most ozone concentrations are found near the mid to high latitudes in the northern and southern hemisphere. The highest ozone concentrations are most commonly found during spring. Most ozone in Antarctica is created at the tropical latitudes; this concentration of ozone at the tropic is then carried by the stratospheric winds to Antarctica, where it is concentrated in great amounts.
It is thought that bromine and chlorine atoms are damaging the ozone layer. The depletion of the ozone layer permits large concentrations of UVB radiation to reach the Earth´s surface. UV radiation can produce a number of effects, including the damaging of the immune system, cancer, eye cataracts, among others. Studies have shown that CFCs and other chemicals contribute with over 80% of the chlorine contained in the stratosphere, while other natural sources produce the other percentage. According to epa.gov, the initial concern about the use of CFCs in the 1970s led to a ban of their use by several nations; however, new uses of CFCs grew rapidly as new uses were discovered.
