¿Que opinais de esto? http://ares.unimet.edu.ve/quimica/fbqi32/contaminacion.asp


El fenómeno que ha recibido mas comentarios en los últimos años es el agujero de la capa de ozono sobre la Antártida, que las teorías prevalecientes en la actualidad atribuyen a los CFCs. Sin embargo ya en 1960, cuando no era tan común el uso de los CFCs, Sir Gordon Dobson demostró la existencia de dicho agujero y atribuyo a las condiciones meteorológicas especiales del continente Antártico.


El invierno antártico se caracteriza por la ausencia de irradiación solar, por las bajisimas temperaturas que se registran en la estratosfera y por el hecho de que soplan vientos de mas de 200 Km por hora, los cuales rodean el continente y aíslan su atmósfera, lo que impide la 

penetración del ozono formado en los trópicos, que llegaría a los polos por acción de otros vientos En tales condiciones, no se renueva el ozono progresivamente destruido.


La Antártida posee doce volcanes activos. El Erebus expulsa, en promedio 1230 toneladas de cloro y 480 toneladas de flúor por día, por lo tanto, disipa anualmente en la atmósfera Antártida cerca de 450 millones de toneladas de cloro, sesenta veces las liberadas por el uso de CFCs. A pesar de ello, la capa de ozono vuelve a la normalidad sobre la Antártida cuando los vientos invernales desaparecen al comenzar la primavera austral.

a mí me parece muy parcial,

la contaminación y el ozono están relacionados, tanto para lo malo, como para lo bueno,

ayer precisamente estaba escribiendo un mensaje aquí, sobre los COV (o VOC en inglés), pero al final lo borré,

la contaminación produce CFCs que destruyen el ozono, pero también produce COV, que son los precursores del ozono troposférico, claro que este es malo
(el ozono en general es malo para el ser humano),

solo falta una buena batidora,...

Cita de: Fortuna en Lunes 11 Mayo 2009 12:24:21 PM
¿Que opinais de esto? http://ares.unimet.edu.ve/quimica/fbqi32/contaminacion.asp


El fenómeno que ha recibido mas comentarios en los últimos años es el agujero de la capa de ozono sobre la Antártida, que las teorías prevalecientes en la actualidad atribuyen a los CFCs. Sin embargo ya en 1960, cuando no era tan común el uso de los CFCs, Sir Gordon Dobson demostró la existencia de dicho agujero y atribuyo a las condiciones meteorológicas especiales del continente Antártico.


El invierno antártico se caracteriza por la ausencia de irradiación solar, por las bajisimas temperaturas que se registran en la estratosfera y por el hecho de que soplan vientos de mas de 200 Km por hora, los cuales rodean el continente y aíslan su atmósfera, lo que impide la 

penetración del ozono formado en los trópicos, que llegaría a los polos por acción de otros vientos En tales condiciones, no se renueva el ozono progresivamente destruido.


La Antártida posee doce volcanes activos. El Erebus expulsa, en promedio 1230 toneladas de cloro y 480 toneladas de flúor por día, por lo tanto, disipa anualmente en la atmósfera Antártida cerca de 450 millones de toneladas de cloro, sesenta veces las liberadas por el uso de CFCs. A pesar de ello, la capa de ozono vuelve a la normalidad sobre la Antártida cuando los vientos invernales desaparecen al comenzar la primavera austral.

Bueno, el Mt. Erebus tiene un índice de explosividad muy bajo (VEI 1-2), por lo que nunca alcanza la estratosfera, ni aunque pensáramos en una mezcla lenta en el tiempo del HCl. La causa es que el HCl es muy soluble, por lo que cuando el vapor de agua alcance el punto de condensación, los derivados clorados precipitarán junto con el agua de lluvia. Se necesita que la inyección de derivados clorados sea directamente en la estratosfera, como en el caso del Pinatubo, amén de los aerosoles, que son los que más juego dan en esto del ozono y volcanes.

No le hagas mucho caso a lo que se dice en ese enlace que has dejado.

Aquí si encontrará muchas respuestas a todas las preguntas que puedas imaginar:

http://www.faqs.org/faqs/ozone-depletion/

esta cita impresiona 

CitarThus _ozone absorbs UV radiation without itself being consumed_;
the net result is to convert UV light into heat. Indeed, this is what causes the temperature of the  stratosphere to increase with altitude, giving rise to the inversion layer that traps molecules in the troposphere.
The ozone layer isn't just _in_ the stratosphere; the ozone layer actually determines the form of the stratosphere.

(extracto del enlace anterior: http://www.faqs.org/faqs/ozone-depletion/intro/)

sobre el pinatubo me parece que no dice lo mismo 

CitarOzone can also be depleted by a major volcanic eruption, such as El Chichon in 1982 or Pinatubo in 1991. The principal mechanism for this is _not_ injection of chlorine into the stratosphere, as discussed in Part II, but rather the injection of sulfate aerosols which change the radiation balance in the stratosphere by scattering light, and which convert inactive chlorine compounds to active, ozone-destroying forms.
[McCormick et al. 1995]. This too is a transient effect, lasting 2-3 years.

bueno, si que dice lo mismo, que la inyección de clorados no es la principal causa (supongo que por lo comentado), y que influyen mucho más los aerosoles de sulfato que inhiben a los clorados.

CitarAquí si encontrará muchas respuestas a todas las preguntas que puedas imaginar:

a.) The Polar Vortex

As the air in the antarctic stratosphere cools and descends during
the winter, the Coriolis effect sets up a strong westerly
circulation around the pole. When the sun returns in the spring the
winds weaken, but the vortex remains stable until November. The air
over antarctica is largely isolated from the rest of the atmosphere,
forming a gigantic reaction vessel. The vortex is not circular, it
has an oblong shape with the long axis extending out over Patagonia.

For further information about the dynamics of the polar vortex see
[Schoeberl and Hartmann], [Tuck 1989], [AASE], [Randel], [Plumb],
and [Waugh]. For a rather short movie (mpeg format) illustrating it,
go to http://daac.gsfc.nasa.gov/CAMPAIGN_DOCS/UARS_project.html.
There is some controversy about just how isolated
the air in the vortex is. Some believe that the vortex is better
thought of as a flow reactor than as a containment vessel; ozone-rich
air enters the vortex from above while ozone-poor and ClO-rich air is
stripped off the sides. Recent tracer measurements lend some support
to this view, but the issue is unresolved. See [Randel] and [Plumb].

b.) Polar Stratospheric Clouds ("PSC")

The Polar vortex is extremely cold; temperatures in the lower
stratosphere drop below -80 C. Under these conditions large numbers
of clouds appear in the stratosphere. These clouds are composed
largely of nitric acid and water, probably in the form of crystals
of nitric acid trihydrate ("NAT"), HNO3.3(H2O). Stratospheric
clouds also form from ordinary water ice (so-called "Type II PSC"),
but these are much less common; the stratosphere is very dry and
water-ice clouds only form at the lowest temperatures.

c.) Reactions On Stratospheric Clouds

Most of the chlorine in the stratosphere ends up in one of the
reservoir compounds, Chlorine Nitrate (ClONO2) or Hydrogen Chloride
(HCl). Laboratory experiments have shown, however, that these
compounds, ordinarily inert in the stratosphere, do react on the
surfaces of polar stratospheric cloud particles. HCl dissolves into
the particles as they grow, and when a ClONO2 molecule becomes
adsorbed the following reactions take place:

ClONO2 + HCl -> Cl2 + HNO3
ClONO2 + H2O -> HOCl + HNO3

The Nitric acid, HNO3, stays in the cloud particle.

In addition, stratospheric clouds catalyze the removal of Nitrogen
Oxides ("NOx"), through the reactions:

N2O5 + H2O -> 2 HNO3
N2O5 + HCl -> ClNO2 + HNO3

Since N2O5 is in (gas-phase) equilibrium  with NO2:

2 N2O5 <-> 4 NO2 + O2

this has the effect of removing NO2 from the gas phase and
sequestering it in the clouds in the form of nitric acid, a process
called "denoxification" (removal of "NOx"). [Crutzen and Arnold]
[Hamill and Toon]

d.) Sedimentation and Denitrification

The clouds may eventually grow big enough so that they settle out
of the stratosphere, carrying the nitric acid with them
("denitrification"). Denitrification enhances denoxification.
If, on the other hand, the cloud decomposes while in the
stratosphere, nitrogen oxides are returned to the gas phase.
Presumably this should be called "renoxification", but
I have not heard anyone use this language :-).

e.) Photolysis of active chlorine compounds

The Cl2 and HOCl produced by the heterogeneous reactions are
easily photolyzed, even in the antarctic winter when there is
little UV present. The sun is always very low in the polar winter,
so the light takes a long path through the atmosphere and the
short-wave UV is selectively absorbed.  Molecular chlorine,
however, absorbs _visible_  and near-UV light:

     Cl2 + hv -> 2 Cl
     Cl + O3 -> ClO + O2

The effect is to produce large amounts of ClO. This ClO would
ordinarily be captured by NO2 and returned to the ClONO2 reservoir,
but "denoxification" and "denitrification" prevent this by removing NO2.

f.) Catalytic destruction of ozone by active chlorine

As discussed in Part I, Cl and ClO can form a catalytic cycle that
efficiently destroys ozone. That cycle used free oxygen atoms,
however, which are only abundant in the upper stratosphere; it
cannot explain the ozone hole which forms in the lower stratosphere.
Instead, the principal mechanism involves chlorine peroxide, ClOOCl
(often referred to as the "ClO dimer") [Molina and Molina]:

     ClO + ClO -> ClOOCl
     ClOOCl + hv -> Cl + ClOO
     ClOO -> Cl + O2
     2 Cl + 2 O3 -> 2 ClO + 2 O2
    -------------------------------
    Net: 2 O3 -> 3 O2

At polar stratospheric temperatures this sequence is extremely fast
and it dominates the ozone-destruction process. The second step,
photolysis of chlorine peroxide, requires UV light which only
becomes abundant in the lower stratosphere in the spring. Thus one
has a long buildup of ClO and ClOOCl during the winter, followed by
massive ozone destruction in the spring. This mechanism is believed
to be responsible for about 70% of the antarctic ozone loss.

_______________________________________________________


Ok, parece que ahora sí me cuadra más, sobre todo por lo que comenta el apartado e). (no me cuadraba el apartado f dado que para obtener ClO se necesitaba radiáción  u.v. o bien, utilizar oxígeno atómico en invierno)

Abro un inciso,

los rayos cósmicos son los precursores de la formación de cloro atmosférico, a partir de Ar36 (el Ar36 por interacción de los rayos cósmicos con Ar40),

vamos, que parece que los rayos cósmicos son también parte fundamental en este proceso, no solo la radiación solar,

¿otro equilibrio semiestable?

Cita de: _00_ en Martes 12 Mayo 2009 23:07:51 PM
Abro un inciso,

los rayos cósmicos son los precursores de la formación de cloro atmosférico, a partir de Ar36 (el Ar36 por interacción de los rayos cósmicos con Ar40),

vamos, que parece que los rayos cósmicos son también parte fundamental en este proceso, no solo la radiación solar,

¿otro equilibrio semiestable?

Efectivammente, "los solar proton events (SPEs)" pueden llegar a generar agujeros en la capa de ozono.

http://elib.suub.uni-bremen.de/diss/docs/00011076.pdf

De nuevo el sol está más presente en la atmósfera (en esta caso en la química) de lo que pensábamos.

10. Summary and conclusions
Different geomagnetic field configurations, of which some are realistic representations for reversal
situations, have been analysed with respect to their influence on atmospheric impacts of
several single solar proton events. Additionally, enabled by a simulated 200 year time series of
SPEs, impacts on longer time scales have been investigated. The simulations have shown that
geomagnetic field variations can have considerable effects on the ozone destructions caused by
solar proton events. In all magnetic shielding scenarios the ozone losses on longer time scales
are most pronounced in the polar regions which indicates the importance of global transport of
NOy and its subsidence into the ozone layer. The atmospheric impacts of single events depend
significantly on the season in which they occur. On average, the ozone destruction is in general
for all considered scenarios larger in the southern hemisphere than in the northern hemisphere.
This is due to hemispheric differences in the transport processes.
In case of the present-day high halogen load in the stratosphere, there is an interference between
halogen chemistry and SPE induced NOy perturbations especially during spring. This somewhat
weakens the immediate SPE impact on ozone, but the general effect is that the anthropogenically
burdened ozone layer is further negatively affected by large SPEs.
The ozone losses are found to increase with the magnetic polar cusp size and with its nearness to
the polar regions. In this sense, the current field configuration with its small tilt of geomagnetic
to geographic axis is almost a worst case situation for the present field strength. The same
cusp size in the tropics would cause much lower ozone destructions. The main reason for this
is the strong photochemical destruction of NOy in combination with the basically nonexistent
downward transport into the ozone layer at low latitudes. The very scenario of an equatorial
dipole of actual cusp size can be regarded as a snap-shot of a hypothetical geomagnetic reversal
with current field strength. As field reversals are very likely connected to field weakenings, they
rather correspond to the other investigated scenarios which lead to significantly enhanced ozone
depletions. For these geomagnetic field configurations, large events are able to cause considerable
ozone losses, especially in the polar regions. With increasing cusp size also mid-latitudes
become affected, but in general to a lesser extent than the polar regions.
For all investigated single SPEs, the total ozone reductions are found to be samller than due
to an ozone hole. Nevertheless, especially in case of a large polar cusps, considerable ozone
losses are found. In contrast to ozone holes, the impacts of SPEs on ozone are less restricted to
spring times and early summer but can last for several years provided that the proton fluences
are large. For exceptionally large SPEs, as they are included in the simulated time series, the
total ozone losses can be comparabel to ozone hole situations. Subsequently, harmful ultraviolet
radiation increases at ground level.
The absolute ozone losses due to SPEs are smaller at mid-latitudes and in the tropics but due to
smaller solar zenith angles the increasing erythemal weighted ultraviolet radiation might also be
of importance in these regions. These results gain importance by the time scales of geomagneticfield variations. For instance, in case of a full field reversal, for thousands of years the protecting
ozone layer at high latitudes would be reduced to a notable extend, and consequently, UV fluxes
would increase for the long time period of the reversal.
It has not been possible within the scope of this study to assess the possible biological impacts
of these increased UV fluxes over time periods of thousands of years. However, it appears as if
SPEs during field reversals are unlikely to directly cause (or have caused) mass-extinctions. On
the other hand, major events in combination with a reduced shielding by the geomagnetic field
have a negative effect on the surface UV burden which could impair living organisms, especially
those how already suffer from other impacts.
The modelled temperature changes which arise from the SPE caused perturbations of the atmosphere's
chemistry are not very large. On average, the temperature tends to decrease in
the middle atmosphere. According to the largest ozone losses, the cooling is strongest in the
antarctic lower stratosphere. There the decreasing temperatures denote a negative feedback on
ozone as they facilitate the formation of polar stratospheric clouds which provide surfaces for
heterogeneous reactions which are important for ozone hole situations in spring times. In terms
of global temperature change, the effect of SPEs seems to be of minor importance, even during
a field reversal.

Aquí hay otro artículo que relaciona los rayos cósmicos con el agujero de ozono.

http://www.science.uwaterloo.ca/~qblu/Lu-2009PRL.pdf

Más cosas sobre las consecuencias negativas producidas por el cierre del agujero

http://translate.googleusercontent.com/translate_c?hl=es&ie=UTF-8&sl=en&tl=es&u=http://www.guardian.co.uk/environment/2009/dec/01/ozone-antarctica&prev=_t&rurl=translate.google.com&usg=ALkJrhjLWPZE756eQfAu3Wo4KQryBAGVzw

un saludo

sobre eso hay que hablar, mucho,

de ese artículo,relacionado con el IPCC:

CitarThis is higher than the rise predicted by the Intergovernmental Panel on Climate Change (IPCC) in 2007, said Turner, because the IPCC's forecasts did not include the impact of melting ice sheets on sea level rises. Muchos de los modelos climáticos utilizados por el IPCC no ha tomado también el agujero de ozono en cuenta en sus simulaciones. Many of the climate models used by the IPCC have also not taken the ozone hole into account in their simulations.

[/size]

lo que nos da una idea de lo bueno que son los modelos, y los parámetros y realimentaciones que barajan, 


sobre el que los CFC hayan "desvanecido" (o estén desvaneciendo" la capa de ozono):

no lo parece, según las mediciones del último ciclo solar (desde el 95), dentro de la media,

http://www.cpc.ncep.noaa.gov/products/stratosphere/sbuv2to/gif_files/

si miramos las anomalías:



....

Si, el ozono juega un papel importante, pero su dinámica está muy relacionada con la actividad solar, lo que lo hace "peligroso" para el IPCC,
sin contar que hay dinámica asociada poco estudiada, como los calentamientos estratosféricos, las burbujas plasmáticas ecuatoriales, los vórtices polares, la química estratosférica, o incluso el tamaño de la atmósfera,

un filtro solar dinámico que afecta a un rango de frecuencias que tiene variaciones cíclicas de hasta el 30%, y que no solo afecta a los polos.

Al ozono también le afecta la crisis.

Si, parece recuperarse,

CitarScientists say the ozone layer is no longer depleting and should regain its density by about 2048.

The first report in four years by the Vienna Convention for the Protection of the Ozone Layer and the Montreal Protocol says the ozone "hole" is recovering more quickly than expected.

Ozone Layer Damage Has Halted