Was a coal miner's lung cancer triggered by coal dust or cigarette smoke? Which is more to blame for a city's poor air quality: diesel buses in the streets or gas-fired turbines at a nearby electric power plant? And how should government target air-pollution-control efforts to best protect human health? The answers to all these questions, John Vander Sande believes, lie in the structure of individual particles of soot.

Scientists concerned about air pollution have long studied concentrations of particulate-or soot-in the air emitted from smokestacks and tailpipes. Some researchers have also looked at the chemical composition of those emissions. But a team of researchers led by Vander Sande, a professor of materials science and engineering at MIT, is the first to mine the wealth of information found in each tiny chunk of impure carbon.

What makes this forensic feat technically possible, Vander Sande explains, is his team's discovery that each soot particle has a unique internal structure-a complex, partially ordered lattice of carbon atoms he dubs a "sootprint." Particles from different sources may also contain traces of different metals or clump together in different shapes-for instance, those discharged by a diesel engine look significantly different from those spewed from a smokestack. In fact, Vander Sande says his group has been able to discern differences in the sootprints that are produced by a diesel engine when it is idling versus when it is revving.

Soot Sources