The article below, shared by RL, is part of a large research project at LBNL:
http://newscenter.lbl.gov/feature-stories/2013/04/10/hidden-dangers-in-the-air-we-breathe/
In the study acrolein and PM2.5, along with the well known formaldehyde, second hand smoke and radon, are the primary pollutants of concern. Really?
RM