For some historical perspective. I've started re-reading William Bramley's Gods of Eden. My colleague Geoff Brady was thinking along the same lines. Eve Lorgen also brought up the connection with Gods of Eden.

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From Geoff: Recent reports about foul-smelling mists and fog causing people to fall ill reminded me of the letters and accounts compiled by author William Bramley who wrote a book entitled Gods of Eden in a recent discussion.

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From the book:

Of all the phenomena connected to the Black Death, by far the most frequently reported were the strange, noxious "mists." The vapors were often observed even when the other phenomena were not. Mr. Nohl points out that moist pestilential fogs were "a feature which preceded the epidemic throughout its whole course." A great many physicians of the time took it for granted that the strange mists caused the Plague. This connection was established at the very beginning of the Black Death, as Mr. Nohl tells us: The origin of the plague lay in China, there it is said to have commenced to rage already in the year 1333, after a terrible mist emitting a fearful stench and infecting the air. Another account stresses that the Plague did not spread from person to person, but was contracted by breathing the deadly stinking air:
 

During the whole of the year 1382 there was no wind, in consequence of which the air grew putrid, so that an epidemic broke out, and the plague did not pass from one man to another, but everyone who was killed by it got it straight from the air. Reports of deadly "mists" and "pestilential fogs" came from all Plague-infested parts of the world: A Prague chronicle describes the epidemic in China, India and Persia; and the Florentine historian Matteo Villani, who took up the work of his brother Giovanni after he had died of the plague in Florence, relays the account of earthquakes and pestilential fogs from a traveler in Asia.
 

The same historian continues: A similar incident of earthquake and pestilential fog was reported from Cyprus, and it was believed that the wind had been so poisonous that men were struck down and died from it. He adds: German accounts speak of a heavy vile-smelling mist which advanced from the East and spread itself over Italy.
 

That author states that in other, people were convinced that they could contract the disease from the stench, or even, as is sometimes described, actually see the plague coming through the streets as a pale fog. He summarizes, rather dramatically: The earth itself seemed in a state of convulsion, shuddering and spitting, putting forth heavy poisonous winds that destroyed animals and plants and called swarms of insects to life to complete the destruction.