Scientists Find New Dangers in Tiny but Pervasive Particles in Air Pollution

Scientists Find New Dangers in Tiny but Pervasive Particles in Air Pollution
http://www.nytimes.com/2012/02/19/science/earth/scientists-find-new-dangers-in-tiny-but-pervasive-particles-in-air-pollution.html?_r=1

"Fine atmospheric particles — smaller than one-thirtieth of the diameter of a human hair — were identified more than 20 years ago as the most lethal of the widely dispersed air pollutants in the United States. Linked to both heart and lung disease, they kill an estimated 50,000 Americans each year. But more recently, scientists have been puzzled to learn that a subset of these particles, called secondary organic aerosols, has a greater total mass, and is thus more dangerous, than previously understood."