In a smallish room, body heat draws particles near, enhancing inhalation

Most models involving inhalation of particulates of various sorts (e.g., microbes, pollen, dust, toxins) assume a somewhat even distribution of the particulates in the air that is inhaled.  While such an assumption helps to simplify exposure calculations, it is factually inaccurate in some circumstances.

Ironically, in small rooms, body heat (in essence thermal plumes) from a person can waft such particulates into breathing range.  A computer simulation of an individual sitting in a room assumed 1,000 particules the size of saliva droplets entered via an air vent.  When the body's surface temperature was 25 degrees C, some of the particles moved/floated upward to the ceiling and then collected overhead.  When the body was at room temperature, fewer particles moved so as to be found over the individual. 

Thus, to some degree (no pun), the body's temperature may influence the number of particulates presented to an individual for inhalation.

The research was presented at the March 16 meeting of the American Physical Society.  An abstract of the presentation can be found at http://meetings.aps.org/Meeting/MAR10/Event/120045.