A Wisdom Archive on skin cancer

The Antarctic ozone hole is an area of the antarctic stratosphere in which the recent ozone levels have dropped to as low as 33% of their pre-1975 values. The ozone hole occurs during the Antarctic spring, from September to early December, as strong westerly winds start to circulate around the continent and create an atmospheric container. Within this "polar vortex", over 50% of the lower stratospheric ozone is destroyed during the antarctic spring.[5] Polar regions get a much larger variation in sunlight than anywhere else, and durin ...

Read more here: » Ozone depletion: Encyclopedia II - Ozone depletion - The ozone hole and its causes

The most pronounced decrease in ozone has been in the lower stratosphere. However, the ozone hole is most usually measured not in terms of ozone concentrations at these levels (which are typically of a few parts per million) but by reduction in the total column ozone, above a point on the Earth's surface, which is normally expressed in Dobson units. Marked decreases in column ozone in the Antarctic spring and early summer compared to the early 1970s and before have been observed using instruments such as ...

Read more here: » Ozone depletion: Encyclopedia II - Ozone depletion - Observations

Ozone depletion - Ozone creation. Ozone in the Earth's atmosphere is generally created by ultraviolet light striking oxygen molecules, which consist of two oxygen atoms (O2), creating two single oxygen atoms, known as atomic oxygen. The atomic oxygen then combines with a molecule of O2 to create ozone, O3. The ozone molecule is rather reactive, and when hit by ultraviolet light it splits again into a molecule of O2 and an atom of atomic oxygen, a continuing process call ...

Read more here: » Ozone depletion: Encyclopedia II - Ozone depletion - Ozone cycle overview

Since the ozone layer absorbs UVB ultraviolet light from the Sun, ozone layer depletion is expected to increase surface UVB levels, which could lead to damage, including increases in skin cancer. This was the reason for the Montreal Protocol. Although decreases in stratospheric ozone are well-tied to CFCs, and there are good theoretical reasons to believe that decreases in ozone will lead to increases in surface UVB, there is not much direct observational evidence linking ozone depletion to higher incidence of skin cancer in human beings. This is partly due to the ...

Read more here: » Ozone depletion: Encyclopedia II - Ozone depletion - Consequences of ozone depletion

Environmentalists assert that the CFCs have caused so much damage to the ozone layer that CFCs should be completely banned. The full extent of the damage CFCs have caused is not known and will not be known for decades; however, marked decreases in column ozone have already been observed (as explained above). After a 1976 report by the U.S. National Academy of Sciences concluded that credible scientific evidence supported the ozone depletion hypothesis, a few countries, including the United States, Canada, Sweden, and Norway, moved to ...

Read more here: » Ozone depletion: Encyclopedia II - Ozone depletion - Public policy in response to the ozone hole

Since the adoption and strengthening of the Montreal Protocol has led to reductions in the emissions of CFCs, atmospheric concentrations of the most significant compounds have been declining. These substances are being gradually removed from the atmosphere. By 2015, the Antarctic ozone hole should have reduced by only 1 million km2 out of 25 (Newman et al, GRL 2004); complete recovery of the A ...

Read more here: » Ozone depletion: Encyclopedia II - Ozone depletion - The future of ozone depletion

There has been a movement since the late 1970s to ban CFCs because of their destructive effect on the ozone layer. This damage was discovered by Sherry Rowland and Mario Molina, who first published a paper suggesting the connection in 1974. It turns out that one of CFCs' most attractive features—their unreactivity—has been instrumental in making them one of the most significant pollutants. CFCs' lack of reactivity gives them a lifespan which can exceed 100 years in some cases. This gives them time to diffuse into the upper stratosphere. ...

Read more here: » Haloalkane: Encyclopedia II - Haloalkane - Environmental issues

A haloalkane, also known as alkyl halogenide, halogenalkane, or halogenoalkane, and alkyl halide is a chemical compound derived from an alkane by substituting one or more hydrogen atoms with halogen atoms. Substitution with fluorine, chlorine, bromine and iodine results in fluoroalkanes, chloroalkanes, bromoalkanes and iodoalkanes, respectively. Mixed compounds are also possible, examples are the chlorofluorocarbons (CFCs) which are mainly responsible for ozone depletion. Haloalk ...

Read more here: » Haloalkane: Encyclopedia II - Haloalkane - General

Alkyl halides can be synthesized from alkanes, alkenes, or alcohols. Haloalkane - From alkanes. Alkanes react with halogens by free radical halogenation. In this reaction a hydrogen atom is removed from the alkane, then replaced by a halogen atom by reaction with a diatomic halogen molecule. Thus: Step 1: X2 → 2 X· (Initiation Step) Step 2: X· + R-H → R· + HX (1st Propagation Step) Step 3: R· + X2 → R-X + ...

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Haloalkanes are reactive towards nucleophiles. They are polar molecules: the carbon to which the halogen is attached is slightly electropositive where the halogen is slightly electronegative. This results in an electron deficient (electrophilic) carbon which, inevitably, attracts nucleophiles. Haloalkane - Substitution reactions. Substitution reactions involve the replacement of the halogen with another molecule - thus leaving ...

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DNA repair - Poor DNA repair induces pathology. As cells get older, the amount of DNA damage accumulates overtaking the rate of repair and resulting in a reduction of protein synthesis. As proteins in the cell are used for numerous vital functions, the cell becomes slowly impaired and eventually dies. When enough cells in an organ reach such a state, the organ itself will become compromised and the symptoms of disease begin to manifest. Experimental studies in animals, where genes associated with DNA repair were ...

Read more here: » DNA repair: Encyclopedia II - DNA repair - DNA repair in disease and aging