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Name: MarĂ­a
Status: student
Age: 17
Location: N/A
Country: N/A
Date: 7/14/2004


Question:
Why do CFC's reach the stratosphere if they are heavier than the air?


Replies:
Maria,

CFCs in the atmosphere exist as gases. Gases have rather weak intermolecular attractions and they exhibit the property of diffusion -- that is, their molecules are in incessant vibrational, rotational, and translational motion. Even though their densities are greater than that of air, CFCs will ultimately mix with and diffuse about in air. In time, some will reach the uppermost parts of earth's atmosphere.

Regards,

ProfHoff 866


Gases, heavier than air, reach high altitudes by convection -- the physical mixing of masses of the atmosphere. Once there CFC's undergo photochemical chain reactions so that a small quantity of CFC's propagate atmosphere-damaging chemical reactions.

Vince Calder


Maria,

Almost any molecule or particle that is not too much heavier than air can be transported long distances horizontally or to great heights vertically by atmospheric motions. For instance, consider the great heights to which thunderstorms can reach, well into the stratosphere. As the air rises in the thunderstorm, it carries with it whatever pollution and particles that were near the surface. Thus they can end up in the stratosphere. Not being too much heavier than air and with little for mechanisms to remove them (little vertical motion, little water vapor, no precipitation, etc.), CFCs can reside in the stratosphere for a long time before they literally fall out down towards the Earth.

David R. Cook
Atmospheric Research Section
Environmental Research Division
Argonne National Laboratory


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