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Ozone Science

Why is the ozone layer threatened?

When released in the air, some very stable chemical products manufactured by men, containing chloride and bromide, gradually infiltrate all zones of the atmosphere, including the stratosphere. Though stable in the low atmosphere, chemical products decompose in the stratosphere due to the high levels of solar UV radiation, releasing very highly reactive chloride and bromide atoms. These participate in a complex series of reactions resulting in ozone depletion. Below there is a simplified version of the main stages of the ozone destruction process.

The free chloride or bromide atoms react with ozone to form chloride or bromide monoxide, taking oxygen atoms and converting the ozone molecule in oxygen. Chloride or bromide monoxide molecules react with free oxygen atoms, leaving their “stolen” oxygen atom to form more molecular oxygen and free chloride or bromide atoms. Chloride or bromide atoms thus released begin again the process attacking another ozone molecule. In this way, each one of these atoms can destroy thousands of ozone molecules, reason for which very reduced amounts of chloride and bromide (in 1985 chloride concentration in the stratosphere was 2.5 parts per thousand millions) can decompose sufficient ozone as to significantly decrease the wide ozone layer.


What is the relationship between ozone depletion and climate?


Atmospheric ozone depletion and climate change are effects from human activities on the global atmosphere. They constitute different environmental problems but are related in several ways. Some of the main possible interactions are the following: chemical products that destroy the ozone layer contribute to the atmosphere warming. Ozone depleting chemical products may affect the thermal balance of the Earth as well as the ozone layer since a large number of them are greenhouse gases. For example, CFC 11 and 12 (the two main chlorofluorocarbon compounds that destroy ozone) are 4000 and 8500 more powerful gases than carbon dioxide, respectively (along a 100-years period). Fluorocarbons developed as CFC substitutes are also potent greenhouse gases.

Ozone depletion can affect climate

Ozone is also a greenhouse gas, and the ozone layer influences the maintenance of the global thermal balance of the planet. Currently it is considered that the ozone layer depletion reduces the greenhouse effect. On the other hand, greater exposure of the Earth's surface to UV-B radiations due to ozone depletion may alter the cycle of greenhouse gases, such as carbon dioxide, in such manner that it could accentuate global warming. Particularly, UV-B increase could end primary production of earth plants and sea phytoplankton, thus reducing the amount of carbon dioxide absorbed from the atmosphere.

Do greenhouse gases affect the recovery of the Ozone Layer?

The effect of greenhouse gases can help the layer recover by cooling the stratosphere, which slows the speed rate of chemical reactions that destroy ozone. But climate change has another effect: It changes patterns of global air circulation.

The results of the chemistry climate model show that an increase in air flow through the mid-southern hemisphere will slow the rate of ozone production there, delaying ozone recovery in places such as Australia and Argentina. Even by the end of the century, the ozone layer in the tropics will not return to pre-1960s levels. Conversely, the United States and other places in the Northern Hemisphere will see enhanced ozone recovery, allowing them to return to mid-20th century ozone levels by about 2030. Ozone recovery at the poles will be minimally affected by climate change.

 How does UV radiation affect human skin?

One of the most evident effects of UV-B radiation is sunburn, known under the technical denomination of erythema. Dark-skin people are protected from most of these effects due to the pigment of their cutaneous cells. UV-B rays can also damage genetic material of said cells, causing cancer.

For clear-skin persons, exposure along their lives to high UV-B levels increase the risk of cutaneous non-melanoma cancer. Researchers have suggested that this type of cancer may increase 2% each time the stratospheric ozone decreases 1 per cent. There are indications that a higher exposure to UV-B, especially during the childhood, may get worse the risk of developing cutaneous melanoma, which are more dangerous.

How do UV radiations affect body's defenses against diseases?

The exposure to UV-B rays can suppress immune responses of human and animal beings. Therefore, an increase of UV-B radiations would reduce human resistance to a series of diseases, like cancers, allergies and some infectious diseases, among others. In zones of the world where infectious diseases constitute an important problem, additional stress derived from a higher UV-B radiation could have significant consequences. This applies especially to diseases like leishmaniasis, malaria and herpes, against which skin is the main defense of the body. Exposure to UV-B can also affect the body's ability to respond to vaccination against diseases. UV-B effects on the immune system do not depend on skin color. Dark-skin people have the same risks as those of clear skin.

What effects do UV rays have on plants?

A great number of plant species and varieties are sensitive to UV-B, even at the current levels. A higher exposure could have direct and indirect complex effects, on both crops and natural ecosystems. Experiments have demonstrated that when crops like rice and soy are more exposed to UV-B radiation, plants are smaller and yield is lower. Increase of UV-B radiation could chemically alter agriculture plants, reducing their nutrition value or increasing their toxicity. If ozone depletion is not stopped, we will have to look for crop varieties tolerating UV-B, or producing others new. Consequences for natural ecosystems are hard to predict but may be considerable.

UV-B radiations have a series of indirect effects on plants, as an alteration of their form, biomass distribution in different parts of the plant and the production of chemical substances that prevent insects attacks. Increase in UV-B radiation could therefore cause effects at ecosystem level, like changes in the competitive equilibrium between plants, animals eating them and the plants pathogen agents and plagues.

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