Torula spp.

Torula spp. from air sample - N. Carlson

From my experience, the yeast Torula spp. is occasionally found in outdoor air samples.  The spores will typically be in chains of three or more with one of the cells broken in half at one end. 

The organism can be identified using tease tapes or a spore trace sample (Air-o-Cell).  It grows on cellulose material (oats, straw, and wicker etc.)  and is reported by EMLab P&K to be allergenic and not pathogenic to humans.