What is the ozone layer?

The following article is the most basic knowledge about ozone layer (ozone), please consult.

What is the ozone layer?

The zone is a layer of atmosphere on the Earth's surface that has a high concentration of ozone. According to the World Meteorological Organization (WMO), the ozone layer in the stratosphere that protects the Earth from the sun's ultraviolet rays takes 5 to 15 years longer than the forecast to fully recover.

The ozone layer in the stratosphere of the Earth is created by the Sun. The ozone molecule is made up of 3 oxygen elements and this structure is not sustainable, but it needs a lot of new energy to be formed. When ultraviolet rays reach the Earth and collide with the oxygen molecule, it separates the oxygen molecule into two oxygen atoms.

When each of these oxygen atoms meets other oxygen molecules, it merges and forms an ozone molecule. This process is called the oxygen-ozone cycle, and it helps convert the energy of ultraviolet rays into heat. , thereby helping to prevent harmful effects of ultraviolet rays on humans. Without the Sun, Earth would not have ozone; but without the Sun, we don't need the ozone.

Earth (EARTH) and ozone layer.

Ozone depletion

Ozone depletion is a phenomenon that reduces the amount of ozone in the stratosphere. Between 1979 and 1990, ozone levels in the stratosphere declined by about 5%. Because the ozone layer prevents most of the harmful ultraviolet rays from passing through the Earth's atmosphere, ozone depletion is being observed and predictions of future decline have become a global concern. , leading to the recognition of the Montreal Protocol, restricting and ultimately ending the use and production of carbon compounds of chlorine and fluorine (CFC - chlorofluorocacbons) as well as other ozone depleting chemicals. such as carbon tetrachloride, bromine (halon) compounds and methylchloroform.

The ozone depletion varies by geography and depends on the season. The ozone hole is used to refer to the temporary annual ozone depletion at the two poles of the Earth, where ozone is depleted in the spring (up to 70% in 25 million km2 of Antarctica and up to 30% in the Arctic. ) and reproduced again in the summer. The concentration of chlorine increases in the stratosphere, which comes when CFCs and other gases produced by humans decompose, causing this decline.

In public political discussions " ozone depletion" means the theory that global ozone depletion, caused by the release of CFCs, will facilitate ultraviolet radiation to the face. more land.

The increasing intensity of ultraviolet radiation is suspected to be the cause of many biological consequences, such as the increase in malignant tumors, destruction of plankton in the lighted layer. of the sea.

Photograph of the largest ozone hole in Antarctica ever since September 2000.

Ozone formation

Ozone in the atmosphere is formed when ultraviolet rays touch oxygen molecules (O ₂ ), containing two oxygen atoms, forming two single oxygen atoms, called atomic oxygen. Atomic oxygen combines with an oxygen molecule to form ozone (O ₃ ). The highly active ozone molecule, when touched by ultraviolet rays, separates into oxygen molecules and an atomic oxygen, a continuous process called the oxygen-cycle.

Before the onset of ozone depletion, the ozone level in the stratosphere is stabilized by balancing the formation and decomposition of ozone molecules thanks to ultraviolet rays.

The cause of ozone hole

The Antarctic ozone hole is part of the Antarctic stratosphere, whose ozone level has now dropped to only 33% compared to the values ​​before 1975. The ozone hole appeared in the Antarctic spring, from September for until early December, when strong western winds begin to circulate on the continent and form atmospheric gourd. In these "polar winds", more than 50% of ozone in the lower stratosphere decomposes in the spring.

Sunlight in polar regions fluctuates more in other places and in the winter months it is almost dark without solar radiation. Air temperatures around -80 ° C or colder almost during the winter have created stratospheric clouds on the extreme. Elements of these clouds include nitric acid or frozen water that forms the surface for chemical reactions that speed up the breakdown of ozone molecules.

As explained above, the main cause of ozone depletion in Antarctica and elsewhere is the presence of chlorine-based gases (primarily CFCs and related carbon chlorine compounds). resolved when ultraviolet light forms chlorine atoms that become ozone catalysts.

The reduction of ozone caused by chlorine is a catalyst that can occur in a gas state but will increase dramatically when there are polar stratospheric clouds present. The involved photochemical processes were complicated but well-understood.

Minimum annual ozone level in Antarctic ozone hole.

The main observation is that most of the chlorine in the aquifer is stored in durable "compounds" , mainly hydrogen chloride (HCl) and chlorine nitrate (ClONO ₂ ). In winter and Antarctic, though, the surface reactions of cloud particles convert these compounds back into highly reactive free radicals, Cl and ClO. Clouds can also take NO ₂ from the atmosphere by converting them into nitric acid, preventing the newly formed ClO from being converted back to ClONO ₂ .

Increased ultraviolet light in the spring causes reactive chlorine compounds to destroy more than 17% of ozone, while brominated substances reduce by 33%. The role of sunlight in reducing ozone is the main reason for the largest reduction in Antarctic ozone in the spring. In the winter, despite being the most cloudy, there is no polar light to promote chemical reactions.

Much of the ozone is destroyed at the bottom of the stratosphere in contrast to the much less ozone depletion through homogeneous gaseous reactions that occur first above the stratosphere. Heating temperatures at the end of Spring break the whirlwinds in the middle of December. When warming, ozone-rich air flies to low latitudes, stratospheric clouds are destroyed, processes to reduce ozone stopped and the ozone hole was healed again.

Consequences of ozone depletion

Because the ozone layer absorbs ultraviolet rays from the sun, reducing the ozone layer is expected to increase the intensity of ultraviolet rays on the Earth's surface, which can lead to many losses including increased skin cancer. That is the reason for the Montreal Protocol. Although the depletion of stratospheric ozone is associated with CFCs and there are many theoretical arguments to believe that ozone depletion will lead to increased ultraviolet light on the Earth's surface, there is not much direct observation. demonstrated a link between ozone depletion and increased rates of skin cancer in humans.