Although this doesn't fully answer the question, I remember doing an exercise in undergraduate P-Chem in the early 1980s in which we were asked to calculate the chances that a breath that we took would contain a molecule (oxygen, nitrogen, carbon dioxide, it didn't matter) of "Caesar's last breath". The answer turned out to be about 50%, so for every few breaths you take, you have a reasonable chance of breathing in a part of "Caesar's last breath". We were asked to ignore effects of material transport, atmospheric convection, chemical reactions, etc., which would be a big part of the answer to the original question posed.
Dear Mr. Ankrah and Mr. Balazs,
At first, I simply glanced at your communication tonight.
I thoght that "Oh, what ary they talking about, how leisurely are they discussing?"
But I suddenly noticed my mistake.
I am a Japanese and am reading roughly newspapaer everymorning.
Do you remember the great failure of Fukusima nuclear power plant, Sirs?
That nuclear power plant has been emanating even now the radioactive substance into the pacific ocean stream. About one year after the great earthquake in Japan, I have heard from the newspaper that at some American coastal region the radioactivity in sea water there, was detected.
It is only one yaer for a radioactive an atom to travel from Asia to North America!
That is a global social problem!
And I am sorry for contaminating the pacific ocean by radioactive substance.
We Japanese usually have been living receiving convenience from that nuclear power plant, without knowing the poignant severe posivility of causing serious fatal disaster for foreign countries.
Is your national sysytem of power plant safe absolutely?
Are you sure?
April 19, 2013