A question for climatologists or similar?

[Flabbergasted]

I heard once that exhaust from cars takes many many years to actually reach the atmosphere. The figure off the top of my head was fifty years.

To take this a step further if this is true then, are we just now seeing gasses from years before finally harming the ozone layer?

[Richard D]

1. I believe . . .

. . . you are mixing up CO2 and fluorocarbons. The CO2 is the gas that traps heat in the atmosphere, the fluorocarbons, from refrigerants and propellants, are what has destroyed the ozone layer over the south pole area. It can take 50 years for the fluorocarbons to get to the ozone layer. Once there, they spend a long time destroying it.

[Flabbergasted]

2. Thank You....

So will the build up of flurocarbons get worse. Fifty years ago we saw a huge rise in their usage?

[Richard D]

4. It may be only 3-5 years

to get to the stratosphere, though I seem to recall seeing 50 years someplace. Maybe that's how long the molecules of chlorine continue to destroy the ozone. There's tons of info on this via google. Here's one site that is quite interesting, though it doesn't answer your question: http://www.ciesin.org/docs/011-464/011-464.html

[Flabbergasted]

5. Thanks Brother!

[Flabbergasted]

3. BTW right on with your pin....!

:yourock:

[mt1000]

6. science facts

see
http://www.thegreatwarming.com

[paul_fromatlanta]

7. Its not the time to reach the atmosphere that's important

CFCs released into the atmosphere become dangerous when they reach the stratisphere..and that can take a few years. But the time after that they remain active without breaking down together with their reactivity is what determine the danger. A single molecule of CFC-12 is the standard and has an ODP (ozone depletion) of 1.0 and takes an average of 111 years to break down and become non-harmful.

Thats right, 111 years.

Methyl Chloroform breaks down in only 8 years and has an ODP of 0.1
while Halon has an ODP of 13 - its 13 times as harmful as CFC12 and breaks down in 110 years.

So even if CFC production stopped to day (and the rate of increase has at least gone to zero) the atmosphere will continue to incur damage for another 100 years.

[Lisa]

8. as other posters have indicated, it depends what part of the atmosphere

The lower layer of the atmosphere, nearest the surface, is called the troposphere. This is where 90% of the atmosphere's mass is -- and it's pretty well-mixed. For example, the monitoring station on the island of Hawaii is able to pick up the seasonal changes in carbon dioxide concentrations. The Intergovernmental Panel on Climate Change (the international scientific organization which co-ordinates a lot of research into global warming) says that vertical mixing of the troposphere (up to almost 20 km above the surface) can happen quite rapidly -- wind patterns, convection, and turbulence likely assist.
"NOx, for instance, has a local lifetime of <1 day in the lower troposphere, but >5 days in the upper troposphere; and both times are less than the time required for vertical mixing of the troposphere. In this case emission of NOx into the upper troposphere will produce a larger atmospheric burden than the same emission into the lower troposphere."
http://www.grida.no/climate/ipcc_tar/wg1/133.htm

Chemicals which are unstable and don't last very long (like some of the compounds generated by photochemical smog formation) tend to be unevenly distributed, while ones that last a long time, like chlorofluorocarbons, are more evenly spread out.
homepages.luc.edu/~mschmel/Handout3.pdf

Higher up, we have the stratosphere -- say in the 20 to 50 km zone. There is a kind of giant temperature inversion which acts as a kind of barrier to air rising up from the surface, and that can slow down the rates at which pollutants can enter the stratosphere. But because the air is a lot thinner up there, and there isn't as much weather activity to wash it out, anything that makes it that high up can stay there for quite some time. Chlorofluorocarbons and other molecules which are exposed to all that ultraviolet light can break apart. This is bad news because it releases atoms of chlorine, etc., which help break apart ozone molecules. Ozone in the troposphere is harmful (causes respiratory problems if you breathe it in), but way up in the stratosphere it helps shield us from UV radiation. The chlorine, bromine, etc. is such an efficient catalyst, and it stays up there for so long, that it can destroy thousands of times its weight in stratospheric ozone. Basically, most of the CFCs that were released back in the 1920s (when they were first invented) are still up there.


The good news is that we've managed to reduce our use of CFCs to the extent that the amount of halogens in the atmosphere has apparently stabilized, and as long as we can restrain ourselves from using ozone-depleting chemicals like methyl bromide, it will begin to drop within a couple of decades, and the ozone layer should be restored to normal by 2100....
(the two horizontal bars at the bottom are natural chlorine and bromine ... the other stuff like CFCs, shown in hot pink, is human-made)


http://www.deh.gov.au/soe/2001/atmosphere.html


Here is the main website for the Vienna Convention (the international treaty which regulates ozone depleting chemicals -- including the Montreal Protocol, which laid out the path for phasing out CFCs). Getting rid of CFCs was a biggie, because they're also implicated in global warming.

http://ozone.unep.org/Public_Information/index.asp

[Richard D]

9. Ah good!

Someone who knows a lot more than me.

One thing I haven't understood is why the ozone layer depletion seems to be worst at the south pole.

Thanks.

[Lisa]

10. some possibilities ...

That's a really good question. The atmospheric chemists I've talked to have noted that the south pole gets colder than the north (especially in the winter) and the answer may be linked to the formation of ice crystals in the atmosphere, which seem to concentrate the ozone-depleting chemicals and otherwise help make the situation more severe. Another theory I've heard is that the low temperatures interfere with chemical reactions (involving nitrogen compounds, I think?) which would otherwise help remove the chlorine from the stratosphere.

more on polar stratospheric clouds:
http://www.atm.ch.cam.ac.uk/tour/psc.html


also relating to earlier questions about how long it takes CFCs to get up to the stratosphere -- I just found out the EPA says 2-5 years.
http://www.epa.gov/ozone/science/q_a.html