il buco nell'Ozono

[fabbio2]

In Origine postato da Luca_liberale
Guarda caso da quando abbiamo dati, il buco c'è......

Da quando abbiamo i dati il buco dell'ozono si e' sempre ingrandito! Ma possibile che certa gente decida di mettersi delle fette di salame sugli occhi e continuare a negare l'evidenza?

[fabbio2]

The ozone hole and its causes
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 during the 3 months of winter spend most of time in the dark without solar radiation. Temperatures hover around or below -80'C for much of the winter, which leads to the formation of polar stratospheric clouds (PSCs). The cloud particles are composed of nitric acid (Type I PSC) or water ice (Type II PSC); both types provide surfaces for chemical reactions that speed the degradation of ozone molecules.

As explained above, the overall cause of ozone depletion, in the antarctic and elsewhere, is the presence of chlorine-containing source gases (primarily CFCs and related halocarbons) which in the presence of UV light are dissociated releasing chlorine atoms which go on to catalyze the destruction of ozone. The Cl-catalyzed ozone depletion can take place in the gas phase, but it is dramatically enhanced in the presence of polar stratospheric clouds. The photochemical processes involved are complex but well understood. The key observation is that ordinarily, most of the chlorine in the stratosphere resides in stable "reservoir" compounds, primarily hydrogen chloride (HCl) and chlorine nitrate (ClONO2). During the antarctic winter and spring, however, reactions on the surface of the cloud particles convert these reservoir compounds back into reactive free radicals, Cl and ClO. The clouds can also remove NO2 from the atmosphere by converting it to nitric acid, preventing the newly formed ClO from being converted back into ClONO2. The role of sunlight in ozone depletion is the reason why the Antarctic ozone depletion is greatest during spring; during winter, even though PSCs are at their most abundant, there is no light over the pole to drive the chemical reactions. Most of the ozone that is destroyed is in the lower stratosphere, in contrast to the much smaller ozone depletion through homogeneous gas phase reactions, which occurs primarily in the upper stratosphere.

Warming temperatures near the end of spring break up the vortex around mid-December. As warm, ozone-rich air flows in from lower latitudes, the PSCs are destroyed, the ozone depletion process shuts down, and the ozone hole heals.

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Interest in ozone hole
While the effect of the Antarctic hole in decreasing the global ozone is relatively small, estimated at about 4% per decade, the hole has generated a great deal of interest because:

The decrease in the ozone layer was predicted in the early 1980's to be roughly 7% over a sixty-year period.
The sudden recognition in 1985 that there was a substantial "hole" was widely reported in the press. The especially rapid ozone depletion in Antarctica had previously been dismissed as measurement error.
Many were worried that ozone holes might start to appear over other areas of the globe but to date the only other large-scale depletion is a smaller ozone "dimple" observed during the Arctic spring over the North Pole. Ozone at middle latitudes has declined, but to a much smaller extent (about 4-5 percent.)
If conditions became more severe (cooler stratospheric temperatures, more stratospheric clouds, more active chlorine) then global ozone may decrease at a much greater pace. Standard global warming theory predicts that the stratosphere will cool.
When the Antarctic ozone hole does break up, the ozone-depleted air drifts out into nearby areas. Decreases in the ozone level of up to 10% have been reported in New Zealand in the month following the break-up of the Antarctic ozone hole.
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Consequences of ozone depletion

Since the ozone layer absorbs ultraviolet light from the Sun, ozone layer depletion is expected to increase surface UV 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 UV, there is not much direct observational evidence linking ozone depletion to higher incidence of skin cancer in human beings.

[fabbio2]

Notare che il protocollo di Montreal fu firmato da George Bush padre, del quale si puo' dire tutto escluso che sia un pericoloso estremista ambientalista e/o comunista.

[Luca_liberale]

In Origine postato da fabbio2
Notare che il protocollo di Montreal fu firmato da George Bush padre, del quale si puo' dire tutto escluso che sia un pericoloso estremista ambientalista e/o comunista.

Ma perchè dovete buttare tutto in politica?